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Schmittwilken L, Wichmann FA, Maertens M. Standard models of spatial vision mispredict edge sensitivity at low spatial frequencies. Vision Res 2024; 222:108450. [PMID: 38964164 DOI: 10.1016/j.visres.2024.108450] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2023] [Revised: 06/11/2024] [Accepted: 06/19/2024] [Indexed: 07/06/2024]
Abstract
One well-established characteristic of early visual processing is the contrast sensitivity function (CSF) which describes how sensitivity varies with the spatial frequency (SF) content of the visual input. The CSF prompted the development of a now standard model of spatial vision. It represents the visual input by activity in orientation- and SF selective channels which are nonlinearly recombined to predict a perceptual decision. The standard spatial vision model has been extensively tested with sinusoidal gratings at low contrast because their narrow SF spectra isolate the underlying SF selective mechanisms. It is less studied how well these mechanisms account for sensitivity to more behaviourally relevant stimuli such as sharp edges at high contrast (i.e. object boundaries) which abound in the natural environment and have broader SF spectra. Here, we probe sensitivity to edges (2-AFC, edge localization) in the presence of broadband and narrowband noises. We use Cornsweet luminance profiles with peak frequencies at 0.5, 3 and 9 cpd as edge stimuli. To test how well mechanisms underlying sinusoidal contrast sensitivity can account for edge sensitivity, we implement a single- and a multi-scale model building upon standard spatial vision model components. Both models account for most of the data but also systematically deviate in their predictions, particularly in the presence of pink noise and for the lowest SF edge. These deviations might indicate a transition from contrast- to luminance-based detection at low SFs. Alternatively, they might point to a missing component in current spatial vision models.
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Affiliation(s)
- Lynn Schmittwilken
- Science of Intelligence and Computational Psychology, Electrical Engineering and Computer Science Technische Universität Berlin, Berlin, Germany.
| | - Felix A Wichmann
- Neural Information Processing, Faculty of Science, University of Tübingen, Tübingen, Germany
| | - Marianne Maertens
- Science of Intelligence and Computational Psychology, Electrical Engineering and Computer Science Technische Universität Berlin, Berlin, Germany
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2
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Poletti M. An eye for detail: Eye movements and attention at the foveal scale. Vision Res 2023; 211:108277. [PMID: 37379763 PMCID: PMC10528557 DOI: 10.1016/j.visres.2023.108277] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 06/08/2023] [Accepted: 06/08/2023] [Indexed: 06/30/2023]
Abstract
Human vision relies on a tiny region of the retina, the 1-deg foveola, to achieve high spatial resolution. Foveal vision is of paramount importance in daily activities, yet its study is challenging, as eye movements incessantly displace stimuli across this region. Here I will review work that, building on recent advances in eye-tracking and gaze-contingent display, examines how attention and eye movements operate at the foveal level. This research highlights how exploration of fine spatial detail unfolds following visuomotor strategies reminiscent of those occurring at larger scales. It shows that, together with highly precise control of attention, this motor activity is linked to non-homogenous processing within the foveola and selectively modulates sensitivity both in space and time. Overall, the picture emerges of a highly dynamic foveal perception in which fine spatial vision, rather than simply being the result of placing a stimulus at the center of gaze, is the result of a finely tuned and orchestrated synergy of motor, cognitive, and attentional processes.
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Affiliation(s)
- Martina Poletti
- Department of Brain and Cognitive Sciences, University of Rochester, United States; Center for Visual Science, University of Rochester, United States; Department of Neuroscience, University of Rochester, United States.
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3
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Meermeier A, Lappe M, Li YH, Rifai K, Wahl S, Rucci M. Fine-scale measurement of the blind spot borders. Vision Res 2023; 211:108208. [PMID: 37454560 PMCID: PMC10494866 DOI: 10.1016/j.visres.2023.108208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Revised: 12/04/2022] [Accepted: 02/20/2023] [Indexed: 07/18/2023]
Abstract
The blind spot is both a necessity and a nuisance for seeing. It is the portion of the visual field projecting to where the optic nerve crosses the retina, a region devoid of photoreceptors and hence visual input. The precise way in which vision transitions into blindness at the blind spot border is to date unknown. A chief challenge to map this transition is the incessant movement of the eye, which unavoidably smears measurements across space. In this study, we used high-resolution eye-tracking and state-of-the-art retinal stabilization to finely map the blind spot borders. Participants reported the onset of tiny high-contrast probes that were briefly flashed at precise positions around the blind spot. This method has sufficient resolution to enable mapping of blood vessels from psychophysical measurements. Our data show that, even after accounting for eye movements, the transition zones at the edges of the blind spot are considerable. On the horizontal meridian, the regions with detection rates between 80% and 20% span approximately 25% of the overall width of the blind spot. These borders also vary considerably in size across different axes. These data show that the transition from full visibility to blindness at the blind spot border is not abrupt but occurs over a broad area.
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Affiliation(s)
- Annegret Meermeier
- Institute for Psychology, University of Muenster, Muenster, Germany; Otto Creutzfeldt Center for Cognitive and Behavioral Neuroscience, University of Muenster, Muenster, Germany
| | - Markus Lappe
- Institute for Psychology, University of Muenster, Muenster, Germany; Otto Creutzfeldt Center for Cognitive and Behavioral Neuroscience, University of Muenster, Muenster, Germany
| | - Yuanhao H Li
- Department of Brain & Cognitive Sciences, University of Rochester, New York, USA; Center for Visual Science, University of Rochester, New York, USA
| | | | - Siegfried Wahl
- Carl Zeiss Vision International GmbH, Aalen, Germany; Institute for Ophthalmic Research, University Tübingen, Tübingen, Germany
| | - Michele Rucci
- Department of Brain & Cognitive Sciences, University of Rochester, New York, USA; Center for Visual Science, University of Rochester, New York, USA
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4
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Becker W, Behler A, Vintonyak O, Kassubek J. Patterns of small involuntary fixation saccades (SIFSs) in different neurodegenerative diseases: the role of noise. Exp Brain Res 2023:10.1007/s00221-023-06633-6. [PMID: 37247026 DOI: 10.1007/s00221-023-06633-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Accepted: 05/09/2023] [Indexed: 05/30/2023]
Abstract
During the attempt to steadily fixate at a single spot, sequences of small involuntary fixation saccades (SIFSs, known also as microsaccades οr intrusions) occur which form spatio-temporal patterns such as square wave jerks (SWJs), a pattern characterised by alternating centrifugal and centripetal movements of similar magnitude. In many neurodegenerative disorders, SIFSs exhibit elevated amplitudes and frequencies. Elevated SIFS amplitudes have been shown to favour the occurrence of SWJs ("SWJ coupling"). We analysed SIFSs in different subject groups comprising both healthy controls (CTR) and patients with amyotrophic lateral sclerosis (ALS) and progressive supranuclear palsy (PSP), i.e. two neurodegenerative diseases with completely different neuropathological basis and different clinical phenotypes. We show that, across these groups, the relations between SIFS amplitude and the relative frequency of SWJ-like patterns and other SIFS characteristics follow a common law. As an explanation, we propose that physiological and technical noise comprises a small, amplitude-independent component that has little effect on large SIFSs, but causes considerable deviations from the intended amplitude and direction of small ones. Therefore, in contrast to large SIFSs, successive small SIFSs have a lower chance to meet the SWJ similarity criteria. In principle, every measurement of SIFSs is affected by an amplitude-independent noise background. Therefore, the dependence of SWJ coupling on SIFS amplitude will probably be encountered in almost any group of subjects. In addition, we find a positive correlation between SIFS amplitude and frequency in ALS, but none in PSP, suggesting that the elevated amplitudes might arise at different sites in the two disorders.
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Affiliation(s)
- Wolfgang Becker
- Section of Neurophysiology, Department of Neurology, University of Ulm, Ulm, Germany.
| | - Anna Behler
- Section of Neurophysiology, Department of Neurology, University of Ulm, Ulm, Germany
- Department of Neurology, University of Ulm, Ulm, Germany
| | - Olga Vintonyak
- Section of Neurophysiology, Department of Neurology, University of Ulm, Ulm, Germany
| | - Jan Kassubek
- Section of Neurophysiology, Department of Neurology, University of Ulm, Ulm, Germany
- Department of Neurology, University of Ulm, Ulm, Germany
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5
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Stanikunas R, Soliunas A, Bliumas R, Jocbalyte K, Novickovas A. Differences in color fading and recovery under sustained fixation. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2023; 40:A33-A39. [PMID: 37133000 DOI: 10.1364/josaa.476533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
More than two centuries ago, Swiss philosopher I. P. V. Troxler announced in 1804 that fixated images fade away during normal vision. Since this declaration, the phenomenon now known as Troxler fading has become the subject of intensive research. Many researchers were eager to find out why we experience image fading and under what conditions image restoration happens. Here, we investigated the dynamics of color stimulus fading and recovery under sustained eye fixation. The objective of the experiments was to find out which colors fade and recover faster under isoluminant conditions. The stimuli were eight blurred color rings extending to 13° in size. Four unique colors (red, yellow, green, and blue) and four intermediate colors (magenta, cyan, yellow-green, and orange) were used. Stimuli were displayed on a computer monitor with a gray background and were isoluminant to the background. The presentation of the stimulus lasted 2 min and subjects were required to look at the fixation point in the middle of the ring and suppress eye movements. The task for subjects was to report the moments of change in the stimulus visibility by four stages of stimulus completeness. We found that all investigated colors undergo fading and recovery cycles during 2 min of observation. The data suggest that magenta and cyan colors have faster stimulus fading and undergo more recovery cycles, while longer wavelength colors slow down stimulus fading.
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Abstract
Human vision relies on mechanisms that respond to luminance edges in space and time. Most edge models use orientation-selective mechanisms on multiple spatial scales and operate on static inputs assuming that edge processing occurs within a single fixational instance. Recent studies, however, demonstrate functionally relevant temporal modulations of the sensory input due to fixational eye movements. Here we propose a spatiotemporal model of human edge detection that combines elements of spatial and active vision. The model augments a spatial vision model by temporal filtering and shifts the input images over time, mimicking an active sampling scheme via fixational eye movements. The first model test was White's illusion, a lightness effect that has been shown to depend on edges. The model reproduced the spatial-frequency-specific interference with the edges by superimposing narrowband noise (1–5 cpd), similar to the psychophysical interference observed in White's effect. Second, we compare the model's edge detection performance in natural images in the presence and absence of Gaussian white noise with human-labeled contours for the same (noise-free) images. Notably, the model detects edges robustly against noise in both test cases without relying on orientation-selective processes. Eliminating model components, we demonstrate the relevance of multiscale spatiotemporal filtering and scale-specific normalization for edge detection. The proposed model facilitates efficient edge detection in (artificial) vision systems and challenges the notion that orientation-selective mechanisms are required for edge detection.
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Affiliation(s)
- Lynn Schmittwilken
- Science of Intelligence and Computational Psychology, Faculty of Electrical Engineering and Computer Science, Technische Universität Berlin, Berlin, Germany.,
| | - Marianne Maertens
- Science of Intelligence and Computational Psychology, Faculty of Electrical Engineering and Computer Science, Technische Universität Berlin, Berlin, Germany.,
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7
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Fixational drift is driven by diffusive dynamics in central neural circuitry. Nat Commun 2022; 13:1697. [PMID: 35361753 PMCID: PMC8971408 DOI: 10.1038/s41467-022-29201-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Accepted: 03/04/2022] [Indexed: 11/08/2022] Open
Abstract
During fixation and between saccades, our eyes undergo diffusive random motion called fixational drift. The role of fixational drift in visual coding and inference has been debated in the past few decades, but the mechanisms that underlie this motion remained unknown. In particular, it has been unclear whether fixational drift arises from peripheral sources, or from central sources within the brain. Here we show that fixational drift is correlated with neural activity, and identify its origin in central neural circuitry within the oculomotor system, upstream to the ocular motoneurons (OMNs). We analyzed a large data set of OMN recordings in the rhesus monkey, alongside precise measurements of eye position, and found that most of the variance of fixational eye drifts must arise upstream of the OMNs. The diffusive statistics of the motion points to the oculomotor integrator, a memory circuit responsible for holding the eyes still between saccades, as a likely source of the motion. Theoretical modeling, constrained by the parameters of the primate oculomotor system, supports this hypothesis by accounting for the amplitude as well as the statistics of the motion. Thus, we propose that fixational ocular drift provides a direct observation of diffusive dynamics in a neural circuit responsible for storage of continuous parameter memory in persistent neural activity. The identification of a mechanistic origin for fixational drift is likely to advance the understanding of its role in visual processing and inference.
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8
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Levinson M, Baillet S. Perceptual filling-in dispels the veridicality problem of conscious perception research. Conscious Cogn 2022; 100:103316. [PMID: 35358869 DOI: 10.1016/j.concog.2022.103316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Revised: 01/13/2022] [Accepted: 03/21/2022] [Indexed: 11/19/2022]
Abstract
Conscious perceptual experiences are expected to correlate with content-specific brain activity. A veridicality problem arises when attempting to disentangle unconscious and conscious brain processes if conscious perceptual contents accurately match the physical nature of the stimulus. We argue that perceptual filling-in, a phenomenon whereby visual information inaccurately spreads across visual space, is a promising approach to circumvent the veridicality problem. Filling-in generates non-veridical although unambiguous percepts dissociated from stimulus input. In particular, the radial uniformity illusion induces a filling-in experience between a central disk and the surrounding periphery. We discuss how this illusion facilitates both the detection of neurophysiological responses and subjective phenomenological monitoring. We report behavioral effects from a large-sample (n = 200) psychophysics study and examine key stimulus parameters that drive the conscious filling-in experience. We propose that these data underpin future hypothesis-driven studies of filling-in to further delineate the neural mechanisms of conscious perception.
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Affiliation(s)
- Max Levinson
- McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montréal, Québec, Canada.
| | - Sylvain Baillet
- McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montréal, Québec, Canada
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9
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Hübner C, Schütz AC. Rapid visual adaptation persists across saccades. iScience 2021; 24:102986. [PMID: 34485868 PMCID: PMC8403744 DOI: 10.1016/j.isci.2021.102986] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 05/28/2021] [Accepted: 07/09/2021] [Indexed: 11/26/2022] Open
Abstract
Neurons in the visual cortex quickly adapt to constant input, which should lead to perceptual fading within few tens of milliseconds. However, perceptual fading is rarely observed in everyday perception, possibly because eye movements refresh retinal input. Recently, it has been suggested that amplitudes of large saccadic eye movements are scaled to maximally decorrelate presaccadic and postsaccadic inputs and thus to annul perceptual fading. However, this argument builds on the assumption that adaptation within naturally brief fixation durations is strong enough to survive any visually disruptive saccade and affect perception. We tested this assumption by measuring the effect of luminance adaptation on postsaccadic contrast perception. We found that postsaccadic contrast perception was affected by presaccadic luminance adaptation during brief periods of fixation. This adaptation effect emerges within 100 milliseconds and persists over seconds. These results indicate that adaptation during natural fixation periods can affect perception even after visually disruptive saccades.
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Affiliation(s)
- Carolin Hübner
- Allgemeine und Biologische Psychologie, Philipps-Universität Marburg, 35037 Marburg, Germany.,Institut für Psychologie, Humboldt-Universität zu Berlin, 12489 Berlin, Germany
| | - Alexander C Schütz
- Allgemeine und Biologische Psychologie, Philipps-Universität Marburg, 35037 Marburg, Germany.,Center for Mind, Brain and Behavior, Philipps-Universität Marburg, 35037 Marburg, Germany
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10
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Curiositas. THE ULSTER MEDICAL JOURNAL 2021; 90:44-45. [PMID: 33642635 PMCID: PMC7907903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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11
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Malevich T, Buonocore A, Hafed ZM. Rapid stimulus-driven modulation of slow ocular position drifts. eLife 2020; 9:e57595. [PMID: 32758358 PMCID: PMC7442486 DOI: 10.7554/elife.57595] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2020] [Accepted: 08/05/2020] [Indexed: 11/17/2022] Open
Abstract
The eyes are never still during maintained gaze fixation. When microsaccades are not occurring, ocular position exhibits continuous slow changes, often referred to as drifts. Unlike microsaccades, drifts remain to be viewed as largely random eye movements. Here we found that ocular position drifts can, instead, be very systematically stimulus-driven, and with very short latencies. We used highly precise eye tracking in three well trained macaque monkeys and found that even fleeting (~8 ms duration) stimulus presentations can robustly trigger transient and stimulus-specific modulations of ocular position drifts, and with only approximately 60 ms latency. Such drift responses are binocular, and they are most effectively elicited with large stimuli of low spatial frequency. Intriguingly, the drift responses exhibit some image pattern selectivity, and they are not explained by convergence responses, pupil constrictions, head movements, or starting eye positions. Ocular position drifts have very rapid access to exogenous visual information.
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Affiliation(s)
- Tatiana Malevich
- Werner Reichardt Centre for Integrative Neuroscience, Tuebingen UniversityTuebingenGermany
- Hertie Institute for Clinical Brain Research, Tuebingen UniversityTuebingenGermany
- Graduate School of Neural and Behavioural Sciences, International Max-Planck Research School, Tuebingen UniversityTuebingenGermany
| | - Antimo Buonocore
- Werner Reichardt Centre for Integrative Neuroscience, Tuebingen UniversityTuebingenGermany
- Hertie Institute for Clinical Brain Research, Tuebingen UniversityTuebingenGermany
| | - Ziad M Hafed
- Werner Reichardt Centre for Integrative Neuroscience, Tuebingen UniversityTuebingenGermany
- Hertie Institute for Clinical Brain Research, Tuebingen UniversityTuebingenGermany
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12
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Roberts MJ, Lange G, Van Der Veen T, Lowet E, De Weerd P. The Attentional Blink is Related to the Microsaccade Rate Signature. Cereb Cortex 2019; 29:5190-5203. [PMID: 30941400 DOI: 10.1093/cercor/bhz058] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Revised: 02/26/2019] [Accepted: 03/02/2019] [Indexed: 11/15/2022] Open
Abstract
The reduced detectability of a target T2 following discrimination of a preceding target T1 in the attentional blink (AB) paradigm is classically interpreted as a consequence of reduced attention to T2 due to attentional allocation to T1. Here, we investigated whether AB was related to changes in microsaccade rate (MSR). We found a pronounced MSR signature following T1 onset, characterized by MSR suppression from 200 to 328 ms and enhancement from 380 to 568 ms. Across participants, the magnitude of the MSR suppression correlated with the AB effect such that low T2 detectability corresponded to reduced MSR. However, in the same task, T1 error trials coincided with the presence of microsaccades. We discuss this apparent paradox in terms of known neurophysiological correlates of MS whereby cortical excitability is suppressed both during the microsaccade and MSR suppression, in accordance to poor T1 performance with microsaccade occurrence and poor T2 performance with microsaccade absence. Our data suggest a novel low-level mechanism contributing to AB characterized by reduced MSR, thought to cause suppressed visual cortex excitability. This opens the question of whether attention mediates T2 performance suppression independently from MSR, and if not, how attention interacts with MSR to produce the T2 performance suppression.
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Affiliation(s)
- Mark J Roberts
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Gesa Lange
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Tracey Van Der Veen
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Eric Lowet
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.,Department of Biology, Boston University, Boston, MA, USA
| | - Peter De Weerd
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.,Maastricht Centre for Systems Biology (MaCSBio), Faculty of Science and Engineering, Maastricht, The Netherlands
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13
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Patrick JA, Roach NW, McGraw PV. Temporal modulation improves dynamic peripheral acuity. J Vis 2019; 19:12. [PMID: 31747690 PMCID: PMC6871547 DOI: 10.1167/19.13.12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Macular degeneration and related visual disorders greatly limit foveal function, resulting in reliance on the peripheral retina for tasks requiring fine spatial vision. Here we investigate stimulus manipulations intended to maximize peripheral acuity for dynamic targets. Acuity was measured using a single interval orientation discrimination task at 10° eccentricity. Two types of image motion were investigated along with two different forms of temporal manipulation. Smooth object motion was generated by translating targets along an isoeccentric path at a constant speed (0-20°/s). Ocular motion was simulated by jittering target location using previously recorded fixational eye movement data, amplified by a variable gain factor (0-8). In one stimulus manipulation, the sequence was temporally subsampled by displaying the target on an evenly spaced subset of video frames. In the other, the contrast polarity of the stimulus was reversed at a variable rate. We found that threshold under object motion was improved at all speeds by reversing contrast polarity, while temporal subsampling improved resolution at high speeds but impaired performance at low speeds. With simulated ocular motion, thresholds were consistently improved by contrast polarity reversal, but impaired by temporal subsampling. We find that contrast polarity reversal and temporal subsampling produce differential effects on peripheral acuity. Applying contrast polarity reversal may offer a relatively simple image manipulation that could enhance visual performance in individuals with central vision loss.
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Affiliation(s)
- Jonathan A Patrick
- Nottingham Visual Neuroscience, The University of Nottingham, Nottingham, UK
| | - Neil W Roach
- Nottingham Visual Neuroscience, The University of Nottingham, Nottingham, UK
| | - Paul V McGraw
- Nottingham Visual Neuroscience, The University of Nottingham, Nottingham, UK
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14
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Rucci M, Ahissar E, Burr D. Temporal Coding of Visual Space. Trends Cogn Sci 2019; 22:883-895. [PMID: 30266148 DOI: 10.1016/j.tics.2018.07.009] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Revised: 07/16/2018] [Accepted: 07/16/2018] [Indexed: 11/20/2022]
Abstract
Establishing a representation of space is a major goal of sensory systems. Spatial information, however, is not always explicit in the incoming sensory signals. In most modalities it needs to be actively extracted from cues embedded in the temporal flow of receptor activation. Vision, on the other hand, starts with a sophisticated optical imaging system that explicitly preserves spatial information on the retina. This may lead to the assumption that vision is predominantly a spatial process: all that is needed is to transmit the retinal image to the cortex, like uploading a digital photograph, to establish a spatial map of the world. However, this deceptively simple analogy is inconsistent with theoretical models and experiments that study visual processing in the context of normal motor behavior. We argue here that, as with other senses, vision relies heavily on temporal strategies and temporal neural codes to extract and represent spatial information.
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Affiliation(s)
- Michele Rucci
- Center for Visual Science, University of Rochester, Rochester, NY 14627, USA; Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY 14627, USA.
| | - Ehud Ahissar
- Department of Neurobiology, Weizmann Institute, Rehovot, Israel.
| | - David Burr
- Department of Neuroscience, University of Florence, Florence 50125, Italy; School of Psychology, University of Sydney, Camperdown, NSW 2006, Australia.
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15
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Becker W, Gorges M, Lulé D, Pinkhardt E, Ludolph AC, Kassubek J. Saccadic intrusions in amyotrophic lateral sclerosis (ALS). J Eye Mov Res 2019; 12:10.16910/jemr.12.6.8. [PMID: 33828758 PMCID: PMC7962685 DOI: 10.16910/jemr.12.6.8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The attempt to quietly fixate at a small visual object is continuously interrupted by a variety of fixational eye movements comprising, among others, a continuum of saccadic intrusions (SI) which range in size from microsaccades with amplitudes ≤0.25° to larger refixation saccades of up to about 2°. The size and frequency of SI varies considerably among individuals and is known to increase in neurodegenerative diseases such as progressive supranuclear palsy (PSP), and amyotrophic lateral sclerosis (ALS). However, studies of ALS disagree whether also the frequency of SI increases. We undertook an analysis of SI in 119 ALS patients and 47 age-matched healthy controls whose eye movements during fixation and tests of executive functions (e.g antisaccades) had been recorded by video-oculography according to standardised procedures. SI were categorised according to their spatio-temporal patterns as stair case, back-and-forth and square wave jerks (a subcategory of back-and-forth). The SI of patients and controls were qualitatively similar (same direction preferences, similar differences between patterns), but were enlarged in ALS. Notably however, no increase of SI frequency could be demonstrated. Yet, there were clear correlations with parameters such as eye blink rate or errors in a delayed saccade task that suggest an impairment of inhibitory mechanisms, in keeping with the notion of a frontal dysfunction in ALS. However, it remains unclear how the impairment of inhibitory mechanisms in ALS could selectively increase the amplitude of intrusions without changing their frequency of occurrence.
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16
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Abstract
OBJECTIVE The objective of this study was to evaluate the impact of directed and sustained attention on the allocation of visuospatial attention. Healthy people often have left lateral and upward vertical spatial attentional biases. However, it is not known whether there will be an increase in bias toward the attended portion of the stimulus when volitional spatial attention is allocated to a portion of a stimulus, whether there are asymmetrical spatial alterations of these biases, and how sustained attention influences these biases. METHODS We assessed spatial bias in 36 healthy, right-handed participants using a variant of horizontal and vertical line bisections. Participants were asked to focus on one or the other end of vertical or horizontal lines or entire vertical or horizontal lines, and then to bisect the line either immediately or after a 20 second delay. RESULTS We found a significant main effect of attentional focus and an interaction between attentional focus and prolonged viewing with delayed bisection. Focusing on a certain portion of the line resulting in a significant deviation toward the attended portion and prolonged viewing of the line prior to bisection significantly enhanced the degree of deviation toward the attended portion. CONCLUSIONS The enhanced bias with directed and sustained attention may be useful modifications of the line bisection test, particularly in clinical populations. Thus, future studies should determine whether prolonged viewing with delayed bisection and spatially focused attention reveals attentional biases in patients with hemispheric lesions who perform normally on the traditional line bisection test. (JINS, 2019, 25, 65-71).
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17
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Soto-Breceda A, Kameneva T, Meffin H, Maturana M, Ibbotson MR. Irregularly timed electrical pulses reduce adaptation of retinal ganglion cells. J Neural Eng 2018; 15:056017. [PMID: 30021932 DOI: 10.1088/1741-2552/aad46e] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
OBJECTIVE Retinal prostheses aim to provide visual percepts to blind people affected by diseases caused by photoreceptor degeneration. One of the main challenges presented by current devices is neural adaptation in the retina, which is believed to be the cause of fading-an effect where artificially produced percepts disappear over a short period of time, despite continuous stimulation of the retina. We aim to understand the neural adaptation generated in retinal ganglion cells (RGCs) during electrical stimulation. APPROACH Current visual prostheses use electrical pulses with fixed frequencies and amplitudes modulated over hundreds of milliseconds to stimulate the retina. However, in nature, neuronal spiking occurs with stochastic timing, hence the information received naturally from other neurons by RGCs is irregularly timed. We used a single epiretinal electrode to stimulate and compare rat RGC responses to stimulus trains of biphasic pulses delivered at regular and random inter-pulse intervals (IPI), the latter taken from an exponential distribution. MAIN RESULTS Our observations suggest that stimulation with random IPIs result in lower adaptation rates than stimulation with constant IPIs at frequencies of 50 Hz and 200 Hz. We also found a high proportion of lower amplitude action potentials, or spikelets. The spikelets were more prominent at high stimulation frequencies (50 Hz and 200 Hz) and were less susceptible to adaptation, but it was not clear if they propagated along the axon. SIGNIFICANCE Using random IPI stimulation in retinal prostheses reduces the decay of RGCs and this could potentially reduce fading of electrically induced visual perception.
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Affiliation(s)
- A Soto-Breceda
- National Vision Research Institute, Australian College of Optometry, Melbourne, Australia. Department of Biomedical Engineering, The University of Melbourne, Melbourne, Australia. CSIRO, Data 61, Melbourne, Australia
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Sheynikhovich D, Bécu M, Wu C, Arleo A. Unsupervised detection of microsaccades in a high-noise regime. J Vis 2018; 18:19. [PMID: 30029229 DOI: 10.1167/18.6.19] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Micromovements of the eye during visual fixations provide clues about how our visual system acquires information. The analysis of fixational eye movements can thus serve as a noninvasive means to detect age-related or pathological changes in visual processing, which can in turn reflect associated cognitive or neurological disorders. However, the utility of such diagnostic approaches relies on the quality and usability of detection methods applied for the eye movement analysis. Here, we propose a novel method for (micro)saccade detection that is resistant to high-frequency recording noise, a frequent problem in video-based eye tracking in either aged subjects or subjects suffering from a vision-related pathology. The method is fast, it does not require manual noise removal, and it can work with position, velocity, or acceleration features, or a combination thereof. The detection accuracy of the proposed method is assessed on a new dataset of manually labeled recordings acquired from 14 subjects of advanced age (69-81 years old), performing an ocular fixation task. It is demonstrated that the detection accuracy of the new method compares favorably to that of two frequently used reference methods and that it is comparable to the best of the two algorithms when tested on an existing low-noise eye-tracking dataset.
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Affiliation(s)
| | - Marcia Bécu
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
| | - Changmin Wu
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
| | - Angelo Arleo
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
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Lowet E, Gips B, Roberts MJ, De Weerd P, Jensen O, van der Eerden J. Microsaccade-rhythmic modulation of neural synchronization and coding within and across cortical areas V1 and V2. PLoS Biol 2018; 16:e2004132. [PMID: 29851960 PMCID: PMC5997357 DOI: 10.1371/journal.pbio.2004132] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2017] [Revised: 06/12/2018] [Accepted: 05/01/2018] [Indexed: 12/13/2022] Open
Abstract
Primates sample their visual environment actively through saccades and microsaccades (MSs). Saccadic eye movements not only modulate neural spike rates but might also affect temporal correlations (synchrony) among neurons. Neural synchrony plays a role in neural coding and modulates information transfer between cortical areas. The question arises of how eye movements shape neural synchrony within and across cortical areas and how it affects visual processing. Through local field recordings in macaque early visual cortex while monitoring eye position and through neural network simulations, we find 2 distinct synchrony regimes in early visual cortex that are embedded in a 3- to 4-Hz MS-related rhythm during visual fixation. In the period shortly after an MS (“transient period”), synchrony was high within and between cortical areas. In the subsequent period (“sustained period”), overall synchrony dropped and became selective to stimulus properties. Only mutually connected neurons with similar stimulus responses exhibited sustained narrow-band gamma synchrony (25–80 Hz), both within and across cortical areas. Recordings in macaque V1 and V2 matched the model predictions. Furthermore, our modeling provides predictions on how (micro)saccade-modulated gamma synchrony in V1 shapes V2 receptive fields (RFs). We suggest that the rhythmic alternation between synchronization regimes represents a basic repeating sampling strategy of the visual system. During visual exploration, we continuously move our eyes in a quick, coordinated manner several times a second to scan our environment. These movements are called saccades. Even while we fixate on a visual object, we unconsciously execute small saccades that are termed microsaccades (MSs). Despite MSs being relatively small, they are suggested to be critical to maintain and support accurate perception during visual fixation. Here, we studied in macaques the influence of MSs on the synchronization of neural rhythms—which are important to regulate information flow in the brain—in areas of the cerebral cortex that are important for early processing of visual information, and we complemented the analysis with computational modeling. We found that synchronization properties shortly after an MS were distinct from synchronization in the later phase. Specifically, we found an early and spectrally broadband synchronization within and between visual cortices that was broadly tuned over the cortical space and stimulus properties. This was followed by narrow-band synchronization in the gamma range (25–80 Hz) that was spatially and stimulus specific. This suggests that the manner in which information is transmitted and integrated between early visual cortices depends on the timing relative to MSs. We illustrate this in a computational model showing that the receptive field (RF) of neurons in the secondary visual cortex are expected to be different depending on MS timing. Our results highlight the significance of MS timing for understanding cortical dynamics and suggest that the regulation of synchronization might be one mechanism by which MSs support visual perception.
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Affiliation(s)
- Eric Lowet
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands
- * E-mail:
| | - Bart Gips
- Radboud University, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, the Netherlands
| | - Mark J. Roberts
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands
| | - Peter De Weerd
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands
- Maastricht Centre for Systems Biology (MaCSBio), Maastricht University, Maastricht, the Netherlands
| | - Ole Jensen
- Centre for Human Brain Health, School of Psychology, University of Birmingham, Birmingham, United Kingdom
| | - Jan van der Eerden
- Radboud University, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, the Netherlands
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Martinez-Conde S, Macknik SL. Unchanging visions: the effects and limitations of ocular stillness. Philos Trans R Soc Lond B Biol Sci 2017; 372:rstb.2016.0204. [PMID: 28242737 DOI: 10.1098/rstb.2016.0204] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/19/2016] [Indexed: 11/12/2022] Open
Abstract
Scientists have pondered the perceptual effects of ocular motion, and those of its counterpart, ocular stillness, for over 200 years. The unremitting 'trembling of the eye' that occurs even during gaze fixation was first noted by Jurin in 1738. In 1794, Erasmus Darwin documented that gaze fixation produces perceptual fading, a phenomenon rediscovered in 1804 by Ignaz Paul Vital Troxler. Studies in the twentieth century established that Jurin's 'eye trembling' consisted of three main types of 'fixational' eye movements, now called microsaccades (or fixational saccades), drifts and tremor. Yet, owing to the constant and minute nature of these motions, the study of their perceptual and physiological consequences has met significant technological challenges. Studies starting in the 1950s and continuing in the present have attempted to study vision during retinal stabilization-a technique that consists on shifting any and all visual stimuli presented to the eye in such a way as to nullify all concurrent eye movements-providing a tantalizing glimpse of vision in the absence of change. No research to date has achieved perfect retinal stabilization, however, and so other work has devised substitute ways to counteract eye motion, such as by studying the perception of afterimages or of the entoptic images formed by retinal vessels, which are completely stable with respect to the eye. Yet other research has taken the alternative tack to control eye motion by behavioural instruction to fix one's gaze or to keep one's gaze still, during concurrent physiological and/or psychophysical measurements. Here, we review the existing data-from historical and contemporary studies that have aimed to nullify or minimize eye motion-on the perceptual and physiological consequences of perfect versus imperfect fixation. We also discuss the accuracy, quality and stability of ocular fixation, and the bottom-up and top-down influences that affect fixation behaviour.This article is part of the themed issue 'Movement suppression: brain mechanisms for stopping and stillness'.
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Affiliation(s)
- Susana Martinez-Conde
- Department of Ophthalmology, State University of New York (SUNY) Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, USA
| | - Stephen L Macknik
- Department of Ophthalmology, State University of New York (SUNY) Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, USA
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Krauzlis RJ, Goffart L, Hafed ZM. Neuronal control of fixation and fixational eye movements. Philos Trans R Soc Lond B Biol Sci 2017; 372:rstb.2016.0205. [PMID: 28242738 PMCID: PMC5332863 DOI: 10.1098/rstb.2016.0205] [Citation(s) in RCA: 121] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/07/2016] [Indexed: 11/17/2022] Open
Abstract
Ocular fixation is a dynamic process that is actively controlled by many of the same brain structures involved in the control of eye movements, including the superior colliculus, cerebellum and reticular formation. In this article, we review several aspects of this active control. First, the decision to move the eyes not only depends on target-related signals from the peripheral visual field, but also on signals from the currently fixated target at the fovea, and involves mechanisms that are shared between saccades and smooth pursuit. Second, eye position during fixation is actively controlled and depends on bilateral activity in the superior colliculi and medio-posterior cerebellum; disruption of activity in these circuits causes systematic deviations in eye position during both fixation and smooth pursuit eye movements. Third, the eyes are not completely still during fixation but make continuous miniature movements, including ocular drift and microsaccades, which are controlled by the same neuronal mechanisms that generate larger saccades. Finally, fixational eye movements have large effects on visual perception. Ocular drift transforms the visual input in ways that increase spatial acuity; microsaccades not only improve vision by relocating the fovea but also cause momentary changes in vision analogous to those caused by larger saccades. This article is part of the themed issue ‘Movement suppression: brain mechanisms for stopping and stillness’.
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Affiliation(s)
- Richard J Krauzlis
- Laboratory of Sensorimotor Research, National Eye Institute, Bethesda, MD, USA
| | | | - Ziad M Hafed
- Werner Reichardt Centre for Integrative Neuroscience, Tuebingen, Germany
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22
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Abstract
Recent research has shown that microsaccades contribute to high acuity vision. However, little is known about whether microsaccades also play a role in daily activities, such as reading, that do not involve stimuli at the limit of spatial resolution. While the functions of larger saccades in reading have been extensively examined, microsaccades are commonly regarded as oculomotor noise in this context. We used high-resolution eyetracking and precise gaze localization to investigate fine oculomotor behavior during reading. Our findings show that microsaccade characteristics differ from those measured during sustained fixation: microsaccades are larger in size and primarily leftwards during reading, i.e. they move the line of sight backward on the text. Analysis of how microsaccades shift gaze relative to the text suggests that these movements serve two important functions: (1) a corrective function, by moving the gaze regressively within longer words when the preceding saccade lands too far toward the end of these words, and (2) an exploratory function, by shifting the gaze on adjacent words to gain additional information before the execution of the next saccade. Thus, microsaccades may benefit reading by enhancing the visibility of nearby words. This study highlights the importance of examining fine oculomotor behavior in reading, and calls for further research to investigate the possible roles of microsaccades in reading difficulties.
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23
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Microsaccade-rate indicates absorption by music listening. Conscious Cogn 2017; 55:59-78. [PMID: 28787663 DOI: 10.1016/j.concog.2017.07.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 07/25/2017] [Accepted: 07/26/2017] [Indexed: 11/22/2022]
Abstract
The power of music is a literary topos, which can be attributed to intense and personally significant experiences, one of them being the state of absorption. Such phenomenal states are difficult to grasp objectively. We investigated the state of musical absorption by using eye tracking. We utilized a load related definition of state absorption: multimodal resources are committed to create a unified representation of music. Resource allocation was measured indirectly by microsaccade rate, known to indicate cognitive processing load. We showed in Exp. 1 that microsaccade rate also indicates state absorption. Hence, there is cross-modal coupling between an auditory aesthetic experience and fixational eye movements. When removing the fixational stimulus in Exp. 2, saccades are no longer generated upon visual input and the cross-modal coupling disappeared. Results are interpreted in favor of the load hypothesis of microsaccade rate and against the assumption of general slowing by state absorption.
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24
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Boi M, Poletti M, Victor JD, Rucci M. Consequences of the Oculomotor Cycle for the Dynamics of Perception. Curr Biol 2017; 27:1268-1277. [PMID: 28434862 DOI: 10.1016/j.cub.2017.03.034] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Revised: 03/11/2017] [Accepted: 03/15/2017] [Indexed: 10/19/2022]
Abstract
Much evidence indicates that humans and other species process large-scale visual information before fine spatial detail. Neurophysiological data obtained with paralyzed eyes suggest that this coarse-to-fine sequence results from spatiotemporal filtering by neurons in the early visual pathway. However, the eyes are normally never stationary: rapid gaze shifts (saccades) incessantly alternate with slow fixational movements. To investigate the consequences of this oculomotor cycle on the dynamics of perception, we combined spectral analysis of visual input signals, neural modeling, and gaze-contingent control of retinal stimulation in humans. We show that the saccade/fixation cycle reformats the flow impinging on the retina in a way that initiates coarse-to-fine processing at each fixation. This finding reveals that the visual system uses oculomotor-induced temporal modulations to sequentially encode different spatial components and suggests that, rather than initiating coarse-to-fine processing, spatiotemporal coupling in the early visual pathway builds on the information dynamics of the oculomotor cycle.
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Affiliation(s)
- Marco Boi
- Department of Psychological and Brain Sciences, Boston University, 2 Cummington Mall, Boston, MA 02215, USA
| | - Martina Poletti
- Department of Psychological and Brain Sciences, Boston University, 2 Cummington Mall, Boston, MA 02215, USA
| | - Jonathan D Victor
- Feil Family Brain and Mind Research Institute, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA
| | - Michele Rucci
- Department of Psychological and Brain Sciences, Boston University, 2 Cummington Mall, Boston, MA 02215, USA; Graduate Program in Neuroscience, Boston University, 2 Cummington Mall, Boston, MA 02215, USA.
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25
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Shaikh AG, Ghasia FF. Fixational saccades are more disconjugate in adults than in children. PLoS One 2017; 12:e0175295. [PMID: 28406944 PMCID: PMC5391133 DOI: 10.1371/journal.pone.0175295] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Accepted: 03/23/2017] [Indexed: 11/18/2022] Open
Abstract
PURPOSE Fixational eye movements are of particular interest for three reasons. They are critical for preventing visual fading and enhancing visual perception; their disconjugacy allows scanning in three dimensions, and their neural correlates span through the cortico-striatal, striato-collicular and brainstem networks. Fixational eye movements are altered in various pediatric ophthalmologic and neurologic disorders. The goal of this study was to compare the dynamics of fixational eye movements in normal children and adults. METHODS We measured the fixational saccades and inter-saccadic drifts in eye positions using infrared video-oculography in children and adults. We assessed the frequency, amplitude, main-sequence, and disconjugacy of fixational saccades as well as the intra-saccadic drift velocity and variance between these two groups. RESULTS We found a similar frequency but an increase in the amplitude of fixational saccades in children compared to adults. We also found that the fixational saccades were more conjugate in children than in adults. The inter-saccadic drifts were comparable between the two groups. DISCUSSION This study provides normative values of dynamics of fixational eye movement in children and adults. The greater disconjugacy of fixational saccades in adults suggests the existence of neural mechanisms that can independently regulate the movements of two eyes. The differences between adult and pediatric populations could be due to completion of the development of binocularly independent regulation of fixational saccades nearing adulthood. The alternate possibility is that the increased disconjugacy between the two eyes may represent a deficiency in the eye movement performance as a function of increasing age.
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Affiliation(s)
- Aasef G. Shaikh
- Department of Neurology, Case Western Reserve University, Cleveland, OH, United States of America
- Neurology service, Louis Stokes Cleveland VA medical center, Cleveland, OH, United States of America
- Daroff-Del’Osso Ocular Motility Laboratory, Louis Stokes Cleveland VA medical center, Cleveland, OH, United States of America
| | - Fatema F. Ghasia
- Daroff-Del’Osso Ocular Motility Laboratory, Louis Stokes Cleveland VA medical center, Cleveland, OH, United States of America
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, United States of America
- * E-mail:
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26
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Yu G, Yang M, Yu P, Dorris MC. Time compression of visual perception around microsaccades. J Neurophysiol 2017; 118:416-424. [PMID: 28298299 DOI: 10.1152/jn.00029.2017] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 03/13/2017] [Accepted: 03/13/2017] [Indexed: 11/22/2022] Open
Abstract
Even during fixation, our eyes are in constant motion. For example, microsaccades are small (typically <1°) eye movements that occur 1~3 times/second. Despite their tiny and transient nature, our percept of visual space is compressed before microsaccades (Hafed ZM, Lovejoy LP, Krauzlis RJ. Eur J Neurosci 37: 1169-1181, 2013). As visual space and time are interconnected at both the physical and physiological levels, we asked whether microsaccades also affect the temporal aspects of visual perception. Here we demonstrate that the perceived interval between transient visual stimuli was compressed if accompanied by microsaccades. This temporal compression extended approximately ±200 ms from microsaccade occurrence, and depending on their particular pattern, multiple microsaccades further enhanced or counteracted this temporal compression. The compression of time surrounding microsaccades resembles that associated with more voluntary macrosaccades (Morrone MC, Ross J, Burr D. Nat Neurosci 8: 950-954, 2005). Our results suggest common neural processes underlying both saccade and microsaccade misperceptions, mediated, likely, through extraretinal mechanisms.NEW & NOTEWORTHY Here we show that humans perceive the duration of visual events as compressed if they are accompanied by microsaccades. Despite the tiny and transient nature of microsaccades, time compression extended more than ±200 ms from their occurrence. Moreover, the number, pattern, and temporal coincidence of microsaccades relative to visual events all contribute to this time misperception. Our results reveal a detailed picture of how our visual time percepts are altered by microsaccades.
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Affiliation(s)
- Gongchen Yu
- Institute of Neuroscience, Key Laboratory of Primate Neurobiology, Chinese Academy of Sciences, Shanghai, China; and.,University of Chinese Academy of Sciences, Shanghai, China
| | - Mingpo Yang
- Institute of Neuroscience, Key Laboratory of Primate Neurobiology, Chinese Academy of Sciences, Shanghai, China; and
| | - Peng Yu
- Institute of Neuroscience, Key Laboratory of Primate Neurobiology, Chinese Academy of Sciences, Shanghai, China; and.,University of Chinese Academy of Sciences, Shanghai, China
| | - Michael Christopher Dorris
- Institute of Neuroscience, Key Laboratory of Primate Neurobiology, Chinese Academy of Sciences, Shanghai, China; and
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27
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Abstract
During steady fixation, observers make small fixational saccades at a rate of around 1–2 per second. Presentation of a visual stimulus triggers a biphasic modulation in fixational saccade rate—an initial inhibition followed by a period of elevated rate and a subsequent return to baseline. Here we show that, during passive viewing, this rate signature is highly sensitive to small changes in stimulus contrast. By training a linear support vector machine to classify trials in which a stimulus is either present or absent, we directly compared the contrast sensitivity of fixational eye movements with individuals' psychophysical judgements. Classification accuracy closely matched psychophysical performance, and predicted individuals' threshold estimates with less bias and overall error than those obtained using specific features of the signature. Performance of the classifier was robust to changes in the training set (novel subjects and/or contrasts) and good prediction accuracy was obtained with a practicable number of trials. Our results indicate a tight coupling between the sensitivity of visual perceptual judgements and fixational eye control mechanisms. This raises the possibility that fixational saccades could provide a novel and objective means of estimating visual contrast sensitivity without the need for observers to make any explicit judgement.
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Affiliation(s)
- Chris Scholes
- Visual Neuroscience Group, School of Psychology, University of Nottingham, Nottingham NG7 2RD, UK
| | - Paul V McGraw
- Visual Neuroscience Group, School of Psychology, University of Nottingham, Nottingham NG7 2RD, UK
| | - Marcus Nyström
- Humanities Laboratory, Lund University, Helgonabacken 12, 22362 Lund, Sweden
| | - Neil W Roach
- Visual Neuroscience Group, School of Psychology, University of Nottingham, Nottingham NG7 2RD, UK
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28
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Abstract
UNLABELLED During visual fixation, the eye generates microsaccades and slower components of fixational eye movements that are part of the visual processing strategy in humans. Here, we show that ongoing heartbeat is coupled to temporal rate variations in the generation of microsaccades. Using coregistration of eye recording and ECG in humans, we tested the hypothesis that microsaccade onsets are coupled to the relative phase of the R-R intervals in heartbeats. We observed significantly more microsaccades during the early phase after the R peak in the ECG. This form of coupling between heartbeat and eye movements was substantiated by the additional finding of a coupling between heart phase and motion activity in slow fixational eye movements; i.e., retinal image slip caused by physiological drift. Our findings therefore demonstrate a coupling of the oculomotor system and ongoing heartbeat, which provides further evidence for bodily influences on visuomotor functioning. SIGNIFICANCE STATEMENT In the present study, we show that microsaccades are coupled to heartbeat. Moreover, we revealed a strong modulation of slow eye movements around the R peak in the ECG. These results suggest that heartbeat as a basic physiological signal is related to statistical modulations of fixational eye movements, in particular, the generation of microsaccades. Therefore, our findings add a new perspective on the principles underlying the generation of fixational eye movements. Importantly, our study highlights the need to record eye movements when studying the influence of heartbeat in neuroscience to avoid misinterpretation of eye-movement-related artifacts as heart-evoked modulations of neural processing.
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Wang QJ, Wang S, Spence C. "Turn Up the Taste": Assessing the Role of Taste Intensity and Emotion in Mediating Crossmodal Correspondences between Basic Tastes and Pitch. Chem Senses 2016; 41:345-56. [PMID: 26873934 PMCID: PMC4840871 DOI: 10.1093/chemse/bjw007] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
People intuitively match basic tastes to sounds of different pitches, and the matches that they make tend to be consistent across individuals. It is, though, not altogether clear what governs such crossmodal mappings between taste and auditory pitch. Here, we assess whether variations in taste intensity influence the matching of taste to pitch as well as the role of emotion in mediating such crossmodal correspondences. Participants were presented with 5 basic tastants at 3 concentrations. In Experiment 1, the participants rated the tastants in terms of their emotional arousal and valence/pleasantness, and selected a musical note (from 19 possible pitches ranging from C2 to C8) and loudness that best matched each tastant. In Experiment 2, the participants made emotion ratings and note matches in separate blocks of trials, then made emotion ratings for all 19 notes. Overall, the results of the 2 experiments revealed that both taste quality and concentration exerted a significant effect on participants' loudness selection, taste intensity rating, and valence and arousal ratings. Taste quality, not concentration levels, had a significant effect on participants' choice of pitch, but a significant positive correlation was observed between individual perceived taste intensity and pitch choice. A significant and strong correlation was also demonstrated between participants' valence assessments of tastants and their valence assessments of the best-matching musical notes. These results therefore provide evidence that: 1) pitch-taste correspondences are primarily influenced by taste quality, and to a lesser extent, by perceived intensity; and 2) such correspondences may be mediated by valence/pleasantness.
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Affiliation(s)
- Qian Janice Wang
- Crossmodal Research Laboratory, Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford OX1 3UD, UK
| | - Sheila Wang
- Crossmodal Research Laboratory, Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford OX1 3UD, UK
| | - Charles Spence
- Crossmodal Research Laboratory, Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford OX1 3UD, UK
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Yu G, Xu B, Zhao Y, Zhang B, Yang M, Kan JYY, Milstein DM, Thevarajah D, Dorris MC. Microsaccade direction reflects the economic value of potential saccade goals and predicts saccade choice. J Neurophysiol 2016; 115:741-51. [PMID: 26609118 DOI: 10.1152/jn.00987.2015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 11/20/2015] [Indexed: 11/22/2022] Open
Abstract
Microsaccades are small-amplitude (typically <1°), ballistic eye movements that occur when attempting to fixate gaze. Initially thought to be generated randomly, it has recently been established that microsaccades are influenced by sensory stimuli, attentional processes, and certain cognitive states. Whether decision processes influence microsaccades, however, is unknown. Here, we adapted two classic economic tasks to examine whether microsaccades reflect evolving saccade decisions. Volitional saccade choices of monkey and human subjects provided a measure of the subjective value of targets. Importantly, analyses occurred during a period of complete darkness to minimize the known influence of sensory and attentional processes on microsaccades. As the time of saccadic choice approached, microsaccade direction became the following: 1) biased toward targets as a function of their subjective value and 2) predictive of upcoming, voluntary choice. Our results indicate that microsaccade direction is influenced by and is a reliable tell of evolving saccade decisions. Our results are consistent with dynamic decision processes within the midbrain superior colliculus; that is, microsaccade direction is influenced by the transition of activity toward caudal saccade regions associated with high saccade value and/or future saccade choice.
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Affiliation(s)
- Gongchen Yu
- Institute of Neuroscience and Key Laboratory of Primate Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; and
| | - Baijie Xu
- Institute of Neuroscience and Key Laboratory of Primate Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; and
| | - Yuchen Zhao
- Institute of Neuroscience and Key Laboratory of Primate Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; and
| | - Beizhen Zhang
- Institute of Neuroscience and Key Laboratory of Primate Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; and
| | - Mingpo Yang
- Institute of Neuroscience and Key Laboratory of Primate Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; and
| | - Janis Ying Ying Kan
- Department of Biomedical and Molecular Sciences, Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
| | - David Martin Milstein
- Department of Biomedical and Molecular Sciences, Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
| | - Dhushan Thevarajah
- Department of Biomedical and Molecular Sciences, Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
| | - Michael Christopher Dorris
- Institute of Neuroscience and Key Laboratory of Primate Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; and
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Fixational saccades during grating detection and discrimination. Vision Res 2016; 118:105-18. [DOI: 10.1016/j.visres.2015.03.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2014] [Revised: 03/25/2015] [Accepted: 03/30/2015] [Indexed: 11/17/2022]
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32
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Abstract
Humans and other species explore a visual scene by rapidly shifting their gaze 2-3 times every second. Although the eyes may appear immobile in the brief intervals in between saccades, microscopic (fixational) eye movements are always present, even when attending to a single point. These movements occur during the very periods in which visual information is acquired and processed and their functions have long been debated. Recent technical advances in controlling retinal stimulation during normal oculomotor activity have shed new light on the visual contributions of fixational eye movements and their degree of control. The emerging body of evidence, reviewed in this article, indicates that fixational eye movements are important components of the strategy by which the visual system processes fine spatial details, enabling both precise positioning of the stimulus on the retina and encoding of spatial information into the joint space-time domain.
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Affiliation(s)
- Michele Rucci
- Department of Psychological & Brain Sciences, Boston University, Boston, MA 02215; Graduate Program in Neuroscience, Boston University, Boston, MA 02215
| | - Martina Poletti
- Department of Psychological & Brain Sciences, Boston University, Boston, MA 02215
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33
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Abstract
Microsaccade rate during fixation is modulated by the presentation of a visual stimulus. When the stimulus is an endogenous attention cue, the ensuing microsaccades tend to be directed toward the cue. This finding has been taken as evidence that microsaccades index the locus of spatial attention. But the vast majority of microsaccades that subjects make are not triggered by visual stimuli. Under natural viewing conditions, spontaneous microsaccades occur frequently (2-3 Hz), even in the absence of a stimulus or a task. While spontaneous microsaccades may depend on low-level visual demands, such as retinal fatigue, image fading, or fixation shifts, it is unknown whether their occurrence corresponds to changes in the attentional state. We developed a protocol to measure whether spontaneous microsaccades reflect shifts in spatial attention. Human subjects fixated a cross while microsaccades were detected from streaming eye-position data. Detection of a microsaccade triggered the appearance of a peripheral ring of grating patches, which were followed by an arrow (a postcue) indicating one of them as the target. The target was either congruent or incongruent (opposite) with respect to the direction of the microsaccade (which preceded the stimulus). Subjects reported the tilt of the target (clockwise or counterclockwise relative to vertical). We found that accuracy was higher for congruent than for incongruent trials. We conclude that the direction of spontaneous microsaccades is inherently linked to shifts in spatial attention.
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34
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Abstract
Microsaccades, the small saccades made when we try to keep the eyes still, were once believed to be inconsequential for vision, but recent studies suggest that they can precisely relocate gaze to tiny visual targets. Because the cerebellum is necessary for motor precision, we investigated whether microsaccades may exploit this neural machinery in monkeys. Almost all vermal Purkinje cells, which provide the eye-related output of the cerebellar cortex, were found to increase or decrease their simple spike firing rate during microsaccades. At both the single-cell and population level, microsaccade-related activity was highly similar to macrosaccade-related activity and we observed a continuous representation of saccade amplitude that spanned both the macrosaccade and microsaccade domains. Our results suggest that the cerebellum's role in fine-tuning eye movements extends even to the oculomotor system's smallest saccades and add to a growing list of observations that call into question the classical categorical distinction between microsaccades and macrosaccades.
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35
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Rucci M, Victor JD. The unsteady eye: an information-processing stage, not a bug. Trends Neurosci 2015; 38:195-206. [PMID: 25698649 PMCID: PMC4385455 DOI: 10.1016/j.tins.2015.01.005] [Citation(s) in RCA: 131] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Revised: 01/20/2015] [Accepted: 01/22/2015] [Indexed: 11/25/2022]
Abstract
How is space represented in the visual system? At first glance, the answer to this fundamental question appears straightforward: spatial information is directly encoded in the locations of neurons within maps. This concept has long dominated visual neuroscience, leading to mainstream theories of how neurons encode information. However, an accumulation of evidence indicates that this purely spatial view is incomplete and that, even for static images, the representation is fundamentally spatiotemporal. The evidence for this new understanding centers on recent experimental findings concerning the functional role of fixational eye movements, the tiny movements humans and other species continually perform, even when attending to a single point. We review some of these findings and discuss their functional implications.
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Affiliation(s)
- Michele Rucci
- Department of Psychological and Brain Sciences, Boston University, Boston, MA 02215, USA; Graduate Program in Neuroscience, Boston University, Boston, MA 02215, USA.
| | - Jonathan D Victor
- Brain and Mind Research Institute, Weill Cornell Medical College, New York, NY 10065, USA
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36
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Sheliga BM, Quaia C, FitzGibbon EJ, Cumming BG. Anisotropy in spatial summation properties of human Ocular-Following Response (OFR). Vision Res 2015; 109:11-9. [PMID: 25743079 DOI: 10.1016/j.visres.2015.02.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Revised: 02/02/2015] [Accepted: 02/04/2015] [Indexed: 10/23/2022]
Abstract
Using sinusoidal gratings we show that an increase in stimulus size confined to the dimension orthogonal to the axis of motion leads to stronger Ocular Following Responses (OFRs) up to a certain optimal size. An increase beyond this optimum produces smaller responses, indicating suppressive interactions. In sharp contrast, when the stimulus growth occurs parallel to the axis of motion OFR magnitudes increase monotonically both for horizontal and vertical directions of motion. Similar results are obtained with 1D white noise patterns. However, the OFR spatial anisotropy is minimal with 2D white noise patterns, revealing a pivotal role of orientation-selective (i.e., cortical) mechanisms in mediating this phenomenon. The lack of anisotropy for 2D patterns suggests that directional signals alone are not sufficient to elicit this suppression. The OFR spatial anisotropy is potentiated if a stationary grating is presented for 600-1000ms before its motion commences, further emphasizing the importance of static orientation signals. These results suggest that the strength of cortical spatial interactions is asymmetric-i.e., larger in the direction of the ends than the flanks of an orientation-selective receptive field-which corroborates the existing neurophysiological evidence.
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Affiliation(s)
- B M Sheliga
- Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA.
| | - C Quaia
- Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - E J FitzGibbon
- Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - B G Cumming
- Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA
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37
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A compact field guide to the study of microsaccades: Challenges and functions. Vision Res 2015; 118:83-97. [PMID: 25689315 DOI: 10.1016/j.visres.2015.01.018] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Revised: 12/30/2014] [Accepted: 01/02/2015] [Indexed: 11/20/2022]
Abstract
Following a period of quiescence at the end of last century, the study of microsaccades has now regained strong impetus and broad attention within the vision research community. This wave of interest, partly fueled by the advent of user-friendly high-resolution eyetrackers, has attracted researchers and led to novel ideas. Old hypothesis have been revisited and new ones formulated. This article is designed to serve as a practical guide for researchers in the field. Because of the history of the field and the difficulty of measuring very small eye movements, the study of microsaccades presents peculiar challenges. Here, we summarize some of the main challenges and describe methods for assessing and improving the quality of the recordings. Furthermore, we examine how these experimental challenges have influenced analysis of the visual functions of microsaccades and critically review current evidence on three long-debated proposals: the maintenance of fixation, the prevention of visual fading, and the exploration of fine spatial detail.
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38
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Wang HX, Yuval-Greenberg S, Heeger DJ. Suppressive interactions underlying visually evoked fixational saccades. Vision Res 2015; 118:70-82. [PMID: 25645962 DOI: 10.1016/j.visres.2015.01.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 11/26/2014] [Accepted: 01/07/2015] [Indexed: 10/24/2022]
Abstract
Small saccades occur frequently during fixation, and are coupled to changes in visual stimulation and cognitive state. Neurophysiologically, fixational saccades reflect neural activity near the foveal region of a continuous visuomotor map. It is well known that competitive interactions between neurons within visuomotor maps contribute to target selection for large saccades. Here we asked how such interactions in visuomotor maps shape the rate and direction of small fixational saccades. We measured fixational saccades during periods of prolonged fixation while presenting pairs of visual stimuli (parafoveal: 0.8° eccentricity; peripheral: 5° eccentricity) of various contrasts. Fixational saccade direction was biased toward locations of parafoveal stimuli but not peripheral stimuli, ∼100-250ms following stimulus onset. The rate of fixational saccades toward parafoveal stimuli (congruent saccades) increased systematically with parafoveal stimulus contrast, and was suppressed by the simultaneous presentation of a peripheral stimulus. The suppression was best characterized as a combination of two processes: a subtractive suppression of the overall fixational saccade rate and a divisive suppression of the direction bias. These results reveal the nature of suppressive interactions within visuomotor maps and constrain models of the population code for fixational saccades.
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Affiliation(s)
- Helena X Wang
- Center for Neural Science, New York University, New York, NY, United States; Dept. of Psychology, New York University, New York, NY, United States
| | - Shlomit Yuval-Greenberg
- Dept. of Psychology, New York University, New York, NY, United States; School of Psychological Sciences and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - David J Heeger
- Center for Neural Science, New York University, New York, NY, United States; Dept. of Psychology, New York University, New York, NY, United States.
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39
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Why have microsaccades become larger? Investigating eye deformations and detection algorithms. Vision Res 2014; 118:17-24. [PMID: 25481631 DOI: 10.1016/j.visres.2014.11.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 11/15/2014] [Accepted: 11/21/2014] [Indexed: 11/20/2022]
Abstract
The reported size of microsaccades is considerably larger today compared to the initial era of microsaccade studies during the 1950s and 1960s. We investigate whether this increase in size is related to the fact that the eye-trackers of today measure different ocular structures than the older techniques, and that the movements of these structures may differ during a microsaccade. In addition, we explore the impact such differences have on subsequent analyzes of the eye-tracker signals. In Experiment I, the movement of the pupil as well as the first and fourth Purkinje reflections were extracted from series of eye images recorded during a fixation task. Results show that the different ocular structures produce different microsaccade signatures. In Experiment II, we found that microsaccade amplitudes computed with a common detection algorithm were larger compared to those reported by two human experts. The main reason was that the overshoots were not systematically detected by the algorithm and therefore not accurately accounted for. We conclude that one reason to why the reported size of microsaccades has increased is due to the larger overshoots produced by the modern pupil-based eye-trackers compared to the systems used in the classical studies, in combination with the lack of a systematic algorithmic treatment of the overshoot. We hope that awareness of these discrepancies in microsaccade dynamics across eye structures will lead to more generally accepted definitions of microsaccades.
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40
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McCamy MB, Macknik SL, Martinez-Conde S. Different fixational eye movements mediate the prevention and the reversal of visual fading. J Physiol 2014; 592:4381-94. [PMID: 25128571 DOI: 10.1113/jphysiol.2014.279059] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Fixational eye movements (FEMs; including microsaccades, drift and tremor) are thought to improve visibility during fixation by thwarting neural adaptation to unchanging stimuli, but how the different FEM types influence this process is a matter of debate. Attempts to answer this question have been hampered by the failure to distinguish between the prevention of fading (where fading is blocked before it happens in the first place) and the reversal of fading (where vision is restored after fading has already occurred). Because fading during fixation is a detriment to clear vision, the prevention of fading, which avoids visual degradation before it happens, is a more desirable scenario than improving visibility after fading has occurred. Yet previous studies have not examined the role of FEMs in the prevention of fading, but have focused on visual restoration instead. Here we set out to determine the differential contributions and efficacies of microsaccades and drift to preventing fading in human vision. Our results indicate that both microsaccades and drift mediate the prevention of visual fading. We also found that drift is a potentially larger contributor to preventing fading than microsaccades, although microsaccades are more effective than drift. Microsaccades moreover prevented foveal and peripheral fading in an equivalent fashion, and their efficacy was independent of their size, number, and direction. Our data also suggest that faster drift may prevent fading better than slower drift. These findings may help to reconcile the long-standing controversy concerning the comparative roles of microsaccades and drift in visibility during fixation.
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Affiliation(s)
- Michael B McCamy
- Department of Neurobiology, Barrow Neurological Institute, Phoenix, AZ, USA School of Mathematical and Statistical Sciences, Arizona State University, Tempe, AZ, USA
| | - Stephen L Macknik
- Department of Neurobiology, Barrow Neurological Institute, Phoenix, AZ, USA Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ, USA
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41
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Figure-ground processing during fixational saccades in V1: indication for higher-order stability. J Neurosci 2014; 34:3247-52. [PMID: 24573283 DOI: 10.1523/jneurosci.4375-13.2014] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In a typical visual scene we continuously perceive a "figure" that is segregated from the surrounding "background" despite ongoing microsaccades and small saccades that are performed when attempting fixation (fixational saccades [FSs]). Previously reported neuronal correlates of figure-ground (FG) segregation in the primary visual cortex (V1) showed enhanced activity in the "figure" along with suppressed activity in the noisy "background." However, it is unknown how this FG modulation in V1 is affected by FSs. To investigate this question, we trained two monkeys to detect a contour embedded in a noisy background while simultaneously imaging V1 using voltage-sensitive dyes. During stimulus presentation, the monkeys typically performed 1-3 FSs, which displaced the contour over the retina. Using eye position and a 2D analytical model to map the stimulus onto V1, we were able to compute FG modulation before and after each FS. On the spatial cortical scale, we found that, after each FS, FG modulation follows the stimulus retinal displacement and "hops" within the V1 retinotopic map, suggesting visual instability. On the temporal scale, FG modulation is initiated in the new retinotopic position before it disappeared from the old retinotopic position. Moreover, the FG modulation developed faster after an FS, compared with after stimulus onset, which may contribute to visual stability of FG segregation, along the timeline of stimulus presentation. Therefore, despite spatial discontinuity of FG modulation in V1, the higher-order stability of FG modulation along time may enable our stable and continuous perception.
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42
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Kosilo M, Wuerger SM, Craddock M, Jennings BJ, Hunt AR, Martinovic J. Low-level and high-level modulations of fixational saccades and high frequency oscillatory brain activity in a visual object classification task. Front Psychol 2014; 4:948. [PMID: 24391611 PMCID: PMC3867122 DOI: 10.3389/fpsyg.2013.00948] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Accepted: 11/30/2013] [Indexed: 11/24/2022] Open
Abstract
Until recently induced gamma-band activity (GBA) was considered a neural marker of cortical object representation. However, induced GBA in the electroencephalogram (EEG) is susceptible to artifacts caused by miniature fixational saccades. Recent studies have demonstrated that fixational saccades also reflect high-level representational processes. Do high-level as opposed to low-level factors influence fixational saccades? What is the effect of these factors on artifact-free GBA? To investigate this, we conducted separate eye tracking and EEG experiments using identical designs. Participants classified line drawings as objects or non-objects. To introduce low-level differences, contours were defined along different directions in cardinal color space: S-cone-isolating, intermediate isoluminant, or a full-color stimulus, the latter containing an additional achromatic component. Prior to the classification task, object discrimination thresholds were measured and stimuli were scaled to matching suprathreshold levels for each participant. In both experiments, behavioral performance was best for full-color stimuli and worst for S-cone isolating stimuli. Saccade rates 200–700 ms after stimulus onset were modulated independently by low and high-level factors, being higher for full-color stimuli than for S-cone isolating stimuli and higher for objects. Low-amplitude evoked GBA and total GBA were observed in very few conditions, showing that paradigms with isoluminant stimuli may not be ideal for eliciting such responses. We conclude that cortical loops involved in the processing of objects are preferentially excited by stimuli that contain achromatic information. Their activation can lead to relatively early exploratory eye movements even for foveally-presented stimuli.
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Affiliation(s)
- Maciej Kosilo
- School of Psychology, University of Aberdeen Aberdeen, UK ; Department of Psychology, City University London London, UK
| | - Sophie M Wuerger
- Department of Psychological Sciences, Institute of Psychology, Health and Society, University of Liverpool Liverpool, UK
| | - Matt Craddock
- Institute for Experimental Psychology and Methods, University of Leipzig Leipzig, Germany
| | - Ben J Jennings
- School of Psychology, University of Aberdeen Aberdeen, UK ; Department of Ophthalmology, McGill Vision Research, McGill University Montreal, QC, Canada
| | - Amelia R Hunt
- School of Psychology, University of Aberdeen Aberdeen, UK
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43
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Roberts JA, Wallis G, Breakspear M. Fixational eye movements during viewing of dynamic natural scenes. Front Psychol 2013; 4:797. [PMID: 24194727 PMCID: PMC3810780 DOI: 10.3389/fpsyg.2013.00797] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Accepted: 10/09/2013] [Indexed: 11/13/2022] Open
Abstract
Even during periods of fixation our eyes undergo small amplitude movements. These movements are thought to be essential to the visual system because neural responses rapidly fade when images are stabilized on the retina. The considerable recent interest in fixational eye movements (FEMs) has thus far concentrated on idealized experimental conditions with artificial stimuli and restrained head movements, which are not necessarily a suitable model for natural vision. Natural dynamic stimuli, such as movies, offer the potential to move beyond restrictive experimental settings to probe the visual system with greater ecological validity. Here, we study FEMs recorded in humans during the unconstrained viewing of a dynamic and realistic visual environment, revealing that drift trajectories exhibit the properties of a random walk with memory. Drifts are correlated at short time scales such that the gaze position diverges from the initial fixation more quickly than would be expected for an uncorrelated random walk. We propose a simple model based on the premise that the eye tends to avoid retracing its recent steps to prevent photoreceptor adaptation. The model reproduces key features of the observed dynamics and enables estimation of parameters from data. Our findings show that FEM correlations thought to prevent perceptual fading exist even in highly dynamic real-world conditions.
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Affiliation(s)
- James A Roberts
- Systems Neuroscience Group, QIMR Berghofer Medical Research Institute Herston, QLD, Australia
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44
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Poletti M, Listorti C, Rucci M. Microscopic eye movements compensate for nonhomogeneous vision within the fovea. Curr Biol 2013; 23:1691-5. [PMID: 23954428 DOI: 10.1016/j.cub.2013.07.007] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Revised: 07/01/2013] [Accepted: 07/02/2013] [Indexed: 10/26/2022]
Abstract
Humans rely on the fovea, the small region of the retina where receptors are most densely packed, for seeing fine spatial detail. Outside the fovea, it is well established that a variety of visual functions progressively decline with eccentricity. In contrast, little is known about how vision varies within the central fovea, as incessant microscopic eye movements prevent isolation of adjacent foveal locations. Using a new method for restricting visual stimulation to a selected retinal region, we examined the discrimination of fine patterns at different eccentricities within the foveola. We show that high-acuity judgments are impaired when stimuli are presented just a few arcminutes away from the preferred retinal locus of fixation. Furthermore, we show that this dependence on eccentricity is normally counterbalanced by the occurrence of precisely directed microsaccades, which bring the preferred fixation locus onto the stimulus. Thus, contrary to common assumptions, vision is not uniform within the foveola, but targeted microscopic eye movements compensate for this lack of homogeneity. Our results reveal that microsaccades, like larger saccades, enable examination of the stimulus at a finer level of detail and suggest that a reduced precision in oculomotor control may be responsible for the visual acuity impairments observed in various disorders.
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Affiliation(s)
- Martina Poletti
- Department of Psychology, Boston University, Boston, MA 02215, USA
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45
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Abstract
Active sensation poses unique challenges to sensory systems because moving the sensor necessarily alters the input sensory stream. Sensory input quality is additionally compromised if the sensor moves rapidly, as during rapid eye movements, making the period immediately after the movement critical for recovering reliable sensation. Here, we studied this immediate postmovement interval for the case of microsaccades during fixation, which rapidly jitter the "sensor" exactly when it is being voluntarily stabilized to maintain clear vision. We characterized retinal-image slip in monkeys immediately after microsaccades by analyzing postmovement ocular drifts. We observed enhanced ocular drifts by up to ~28% relative to premicrosaccade levels, and for up to ~50 ms after movement end. Moreover, we used a technique to trigger full-field image motion contingent on real-time microsaccade detection, and we used the initial ocular following response to this motion as a proxy for changes in early visual motion processing caused by microsaccades. When the full-field image motion started during microsaccades, ocular following was strongly suppressed, consistent with detrimental retinal effects of the movements. However, when the motion started after microsaccades, there was up to ~73% increase in ocular following speed, suggesting an enhanced motion sensitivity. These results suggest that the interface between even the smallest possible saccades and "fixation" includes a period of faster than usual image slip, as well as an enhanced responsiveness to image motion, and that both of these phenomena need to be considered when interpreting the pervasive neural and perceptual modulations frequently observed around the time of microsaccades.
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46
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Martinez-Conde S, Otero-Millan J, Macknik SL. The impact of microsaccades on vision: towards a unified theory of saccadic function. Nat Rev Neurosci 2013; 14:83-96. [PMID: 23329159 DOI: 10.1038/nrn3405] [Citation(s) in RCA: 277] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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47
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Thaler L, Schütz A, Goodale M, Gegenfurtner K. What is the best fixation target? The effect of target shape on stability of fixational eye movements. Vision Res 2013; 76:31-42. [DOI: 10.1016/j.visres.2012.10.012] [Citation(s) in RCA: 176] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2012] [Revised: 10/12/2012] [Accepted: 10/13/2012] [Indexed: 11/25/2022]
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48
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Abstract
Our eyes move constantly, even when we try to fixate our gaze. Fixational eye movements prevent and restore visual loss during fixation, yet the relative impact of each type of fixational eye movement remains controversial. For over five decades, the debate has focused on microsaccades, the fastest and largest fixational eye movements. Some recent studies have concluded that microsaccades counteract visual fading during fixation. Other studies have disputed this idea, contending that microsaccades play no significant role in vision. The disagreement stems from the lack of methods to determine the precise effects of microsaccades on vision versus those of other eye movements, as well as a lack of evidence that microsaccades are relevant to foveal vision. Here we developed a novel generalized method to determine the precise quantified contribution and efficacy of human microsaccades to restoring visibility compared with other eye movements. Our results indicate that microsaccades are the greatest eye movement contributor to the restoration of both foveal and peripheral vision during fixation. Our method to calculate the efficacy and contribution of microsaccades to perception can determine the strength of connection between any two physiological and/or perceptual events, providing a novel and powerful estimate of causal influence; thus, we anticipate wide-ranging applications in neuroscience and beyond.
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49
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Abstract
The significance of the miniature eye movements that we make during visual fixation has been intensely debated for the last 80 years. Recent studies have revealed that these motions of the eyes fulfill an important functional role: helping to extract useful information from natural scenes.
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Affiliation(s)
- Igor Kagan
- German Primate Center, Kellnerweg 4, 37077 Goettingen, Germany.
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50
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Cherici C, Kuang X, Poletti M, Rucci M. Precision of sustained fixation in trained and untrained observers. J Vis 2012; 12:31. [PMID: 22728680 PMCID: PMC3489479 DOI: 10.1167/12.6.31] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2011] [Accepted: 05/05/2012] [Indexed: 11/24/2022] Open
Abstract
During visual fixation, microscopic eye movements shift the image on the retina over a large number of photoreceptors. Although these movements have been investigated for almost a century, the amount of retinal image motion they create remains unclear. Currently available estimates rely on assumptions about the probability distributions of eye movements that have never been tested. Furthermore, these estimates were based on data collected with only a few, highly experienced and motivated observers and may not be representative of the instability of naive and inexperienced subjects in experiments that require steady fixation. In this study, we used a high-resolution eye-tracker to estimate the probability distributions of gaze position in a relatively large group of human observers, most of whom were untrained, while they were asked to maintain fixation at the center of a uniform field in the presence/absence of a fixation marker. In all subjects, the probability distribution of gaze position deviated from normality, the underlying assumption of most previous studies. The resulting fixational dispersion of gaze was much larger than previously reported and varied greatly across individuals. Unexpectedly, the precision by which different observers maintained fixation on the marker was best predicted by the properties of ocular drift rather than those of microsaccades. Our results show that, during fixation, the eyes move by larger amounts and at higher speeds than commonly assumed and highlight the importance of ocular drift in maintaining accurate fixation.
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Affiliation(s)
- Claudia Cherici
- Department of Psychology, Boston University, Boston, MA, USA
| | - Xutao Kuang
- Department of Psychology, Boston University, Boston, MA, USA
| | - Martina Poletti
- Department of Psychology, Boston University, Boston, MA, USA
| | - Michele Rucci
- Department of Psychology, Boston University, Boston, MA, USA
- Graduate Program in Neuroscience, Boston University, Boston, MA, USA
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