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Gao Y, Webster MA, Jiang F. Dynamics of contrast adaptation in central and peripheral vision. J Vis 2019; 19:23. [PMID: 31251807 PMCID: PMC6602361 DOI: 10.1167/19.6.23] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Accepted: 05/27/2019] [Indexed: 11/24/2022] Open
Abstract
Adaptation aftereffects are generally stronger for peripheral than for foveal viewing. We examined whether there are also differences in the dynamics of visual adaptation in central and peripheral vision. We tracked the time course of contrast adaptation to binocularly presented Gabor patterns in both the central visual field (within 5°) and in the periphery (beyond 10° eccentricity) using a yes/no detection task to monitor contrast thresholds. Consistent with previous studies, sensitivity losses were stronger in the periphery than in the center when adapting to equivalent high contrast (90% contrast) patterns. The time course of the threshold changes was fitted with separate exponential functions to estimate the time constants during the adapt and post-adapt phases. When adapting to equivalent high contrast, adaptation effects built up and decayed more slowly in the periphery compared with central adaptation. Surprisingly, the aftereffect in the periphery did not decay completely to the baseline within the monitored post-adapt period (400 s), and instead asymptoted to a higher level than for central adaptation. Even when contrast was reduced to one-third (30% contrast) of the central contrast, peripheral adaptation remained stronger and decayed more slowly. This slower dynamic was also confirmed at suprathreshold test contrasts by tracking tilt-aftereffects with a 2AFC orientation discrimination task. Our results indicate that the dynamics of contrast adaptation differ between central and peripheral vision, with the periphery adapting not only more strongly but also more slowly, and provide another example of potential qualitative processing differences between central and peripheral vision.
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Yoshimoto S, Jiang F, Takeuchi T, Wilkins AJ, Webster MA. Adaptation and visual discomfort from flicker. Vision Res 2019; 160:99-107. [PMID: 31091424 DOI: 10.1016/j.visres.2019.04.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Revised: 04/21/2019] [Accepted: 04/24/2019] [Indexed: 10/26/2022]
Abstract
Spatial images with unnatural amplitude spectra tend to appear uncomfortable. Analogous effects are found in the temporal domain, yet discomfort in flickering patterns is also strongly dependent on the phase spectrum. Here we examined how discomfort in temporal flicker is affected by adaptation to different amplitude and phase spectra. Adapting and test flicker were square wave or random phase transitions in a uniform field filtered by increasing (blurred) or decreasing (sharpened) the slope of the amplitude spectrum. Participants rated the level of discomfort or sharpness/blur for the test flicker. Before adaptation, square wave transitions were rated as most comfortable when they had "focused" edges, which were defined as characterized by 1/f amplitude spectra, while random phase transitions instead appeared more comfortable the more blurred they were. After adapting to blurred or sharpened transitions, both square wave and random phase flicker appeared more sharpened or blurred, respectively, and these effects were consistent with renormalization of perceived temporal focus. In comparison, adaptation affected discomfort in the two waveforms in qualitatively different ways, and exposure to the adapting stimulus tended to increase rather than decreased its perceived discomfort. These results point to a dissociation between the perceived amplitude spectrum and perceived discomfort, suggesting they in part depend on distinct processes. The results further illustrate the importance of the phase spectrum in determining visual discomfort from flickering patterns.
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Gwinn OS, Matera CN, O'Neil SF, Webster MA. Asymmetric neural responses for facial expressions and anti-expressions. Neuropsychologia 2018; 119:405-416. [PMID: 30193846 PMCID: PMC6191349 DOI: 10.1016/j.neuropsychologia.2018.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2018] [Revised: 08/27/2018] [Accepted: 09/02/2018] [Indexed: 01/23/2023]
Abstract
Face recognition requires identifying both the invariant characteristics that distinguish one individual from another and the variations within the individual that correspond to emotional expressions. Both have been postulated to be represented via a norm-based code, in which identity or expression are represented as deviations from an average or neutral prototype. We used Fast Periodic Visual Stimulation (FPVS) with electroencephalography (EEG) to compare neural responses for neutral faces, expressions and anti-expressions. Anti-expressions are created by projecting an expression (e.g. a happy face) through the neutral face to form the opposite facial shape (anti-happy). Thus expressions and anti-expressions differ from the norm by the same "configural" amount and thus have equivalent but opposite status with regard to their shape, but differ in their ecological validity. We examined whether neural responses to these complementary stimulus pairs were equivalent or asymmetric, and also tested for norm-based coding by comparing whether stronger responses are elicited by expressions and anti-expressions than neutral faces. Observers viewed 20 s sequences of 6 Hz alternations of neutral faces and expressions, neutral faces and anti-expressions, and expressions and anti-expressions. Responses were analyzed in the frequency domain. Significant responses at half the frequency of the presentation rate (3 Hz), indicating asymmetries in responses, were observed for all conditions. Inversion of the images reduced the size of this signal, indicating these asymmetries are not solely due to differences in the low-level properties of the images. While our results do not preclude a norm-based code for expressions, similar to identity, this representation (as measured by the FPVS EEG responses) may also include components sensitive to which configural distortions form meaningful expressions.
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Retter TL, Jiang F, Webster MA, Rossion B. Dissociable effects of inter-stimulus interval and presentation duration on rapid face categorization. Vision Res 2018; 145:11-20. [PMID: 29581059 DOI: 10.1016/j.visres.2018.02.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Revised: 02/07/2018] [Accepted: 02/08/2018] [Indexed: 10/17/2022]
Abstract
Fast periodic visual stimulation combined with electroencephalography (FPVS-EEG) has unique sensitivity and objectivity in measuring rapid visual categorization processes. It constrains image processing time by presenting stimuli rapidly through brief stimulus presentation durations and short inter-stimulus intervals. However, the selective impact of these temporal parameters on visual categorization is largely unknown. Here, we presented natural images of objects at a rate of 10 or 20 per second (10 or 20 Hz), with faces appearing once per second (1 Hz), leading to two distinct frequency-tagged EEG responses. Twelve observers were tested with three squarewave image presentation conditions: 1) with an ISI, a traditional 50% duty cycle at 10 Hz (50-ms stimulus duration separated by a 50-ms ISI); 2) removing the ISI and matching the rate, a 100% duty cycle at 10 Hz (100-ms duration with 0-ms ISI); 3) removing the ISI and matching the stimulus presentation duration, a 100% duty cycle at 20 Hz (50-ms duration with 0-ms ISI). The face categorization response was significantly decreased in the 20 Hz 100% condition. The conditions at 10 Hz showed similar face-categorization responses, peaking maximally over the right occipito-temporal (ROT) cortex. However, the onset of the 10 Hz 100% response was delayed by about 20 ms over the ROT region relative to the 10 Hz 50% condition, likely due to immediate forward-masking by preceding images. Taken together, these results help to interpret how the FPVS-EEG paradigm sets temporal constraints on visual image categorization.
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Buck SL, Baraas R, Kremers J, Lindsey DT, Nascimento SMC, Webster MA, Werner JS. Color Vision 2018: Introduction by the feature editors. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2018; 35:CV1-CV2. [PMID: 29603947 DOI: 10.1364/josaa.35.000cv1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Indexed: 06/08/2023]
Abstract
This feature issue of the Journal of the Optical Society of America A (JOSA A) reflects the basic and applied research interests of members of the color vision community. Most of the articles stem from presentations at the 24th Biennial Symposium of the International Colour Vision Society (ICVS).
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Kompaniez-Dunigan E, Abbey CK, Boone JM, Webster MA. Visual adaptation and the amplitude spectra of radiological images. COGNITIVE RESEARCH-PRINCIPLES AND IMPLICATIONS 2018; 3:3. [PMID: 29399622 PMCID: PMC5783991 DOI: 10.1186/s41235-018-0089-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/22/2017] [Accepted: 01/04/2018] [Indexed: 11/25/2022]
Abstract
We examined how visual sensitivity and perception are affected by adaptation to the characteristic amplitude spectra of X-ray mammography images. Because of the transmissive nature of X-ray photons, these images have relatively more low-frequency variability than natural images, a difference that is captured by a steeper slope of the amplitude spectrum (~ − 1.5) compared to the ~ 1/f (slope of − 1) spectra common to natural scenes. Radiologists inspecting these images are therefore exposed to a different balance of spectral components, and we measured how this exposure might alter spatial vision. Observers (who were not radiologists) were adapted to images of normal mammograms or the same images sharpened by filtering the amplitude spectra to shallower slopes. Prior adaptation to the original mammograms significantly biased judgments of image focus relative to the sharpened images, demonstrating that the images are sufficient to induce substantial after-effects. The adaptation also induced strong losses in threshold contrast sensitivity that were selective for lower spatial frequencies, though these losses were very similar to the threshold changes induced by the sharpened images. Visual search for targets (Gaussian blobs) added to the images was also not differentially affected by adaptation to the original or sharper images. These results complement our previous studies examining how observers adapt to the textural properties or phase spectra of mammograms. Like the phase spectrum, adaptation to the amplitude spectrum of mammograms alters spatial sensitivity and visual judgments about the images. However, unlike the phase spectrum, adaptation to the amplitude spectra did not confer a selective performance advantage relative to more natural spectra.
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Mollon JD, Bosten JM, Peterzell DH, Webster MA. Individual differences in visual science: What can be learned and what is good experimental practice? Vision Res 2017; 141:4-15. [PMID: 29129731 PMCID: PMC5730466 DOI: 10.1016/j.visres.2017.11.001] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Revised: 11/07/2017] [Accepted: 11/08/2017] [Indexed: 01/21/2023]
Abstract
We all pass out our lives in private perceptual worlds. The differences in our sensory and perceptual experiences often go unnoticed until there emerges a variation (such as 'The Dress') that is large enough to generate different descriptions in the coarse coinage of our shared language. In this essay, we illustrate how individual differences contribute to a richer understanding of visual perception, but we also indicate some potential pitfalls that face the investigator who ventures into the field.
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Bosten JM, Mollon JD, Peterzell DH, Webster MA. Individual differences as a window into the structure and function of the visual system. Vision Res 2017; 141:1-3. [DOI: 10.1016/j.visres.2017.11.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Yoshimoto S, Garcia J, Jiang F, Wilkins AJ, Takeuchi T, Webster MA. Visual discomfort and flicker. Vision Res 2017; 138:18-28. [PMID: 28709920 DOI: 10.1016/j.visres.2017.05.015] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Revised: 04/11/2017] [Accepted: 05/25/2017] [Indexed: 11/18/2022]
Abstract
Flickering lights can be uncomfortable to look at and can induce seizures in observers with photosensitive epilepsy. However, the temporal characteristics contributing to these effects are not fully known. In the spatial domain, one identified source of visual discomfort is when images have Fourier amplitude spectra that deviate from the natural (∼1/frequency, 1/f) statistical characteristics of natural scenes, especially if they contain excess energy at the medium frequencies at which the visual system is most sensitive. We tested for analogous effects in the temporal domain, manipulating both the amplitude and phase spectra of the flicker. Participants judged the relative discomfort of temporal luminance variations in a pair of uniform 17° fields with different temporal modulations. In general, discomfort increased with deviations from natural amplitude spectra, particularly those with excess energy at medium frequencies or biased toward sharper spectra. These ratings of discomfort were also consistent with ratings of how natural the modulations appeared. However, the temporal discomfort judgments were also strongly affected by the phase spectra of the flicker, with fixed vs. random spectra producing very different responses. This was not due to the perceived regularity or predictability of the flicker, but could arise from a number of other potential factors. Our findings suggest that, like spatial patterns, visual discomfort in time-varying patterns depends in part on how similar they are to the amplitude spectra of temporal variations in the natural visual environment, but also point to the critical role of the phase spectrum in the perceived discomfort of flicker.
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Abstract
Many techniques have been developed to visualize how an image would appear to an individual with a different visual sensitivity: e.g., because of optical or age differences, or a color deficiency or disease. This protocol describes a technique for incorporating sensory adaptation into the simulations. The protocol is illustrated with the example of color vision, but is generally applicable to any form of visual adaptation. The protocol uses a simple model of human color vision based on standard and plausible assumptions about the retinal and cortical mechanisms encoding color and how these adjust their sensitivity to both the average color and range of color in the prevailing stimulus. The gains of the mechanisms are adapted so that their mean response under one context is equated for a different context. The simulations help reveal the theoretical limits of adaptation and generate "adapted images" that are optimally matched to a specific environment or observer. They also provide a common metric for exploring the effects of adaptation within different observers or different environments. Characterizing visual perception and performance with these images provides a novel tool for studying the functions and consequences of long-term adaptation in vision or other sensory systems.
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Emery KJ, Volbrecht VJ, Peterzell DH, Webster MA. Variations in normal color vision. VI. Factors underlying individual differences in hue scaling and their implications for models of color appearance. Vision Res 2017; 141:51-65. [PMID: 28025051 DOI: 10.1016/j.visres.2016.12.006] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 12/02/2016] [Accepted: 12/06/2016] [Indexed: 11/17/2022]
Abstract
Observers with normal color vision vary widely in their judgments of color appearance, such as the specific spectral stimuli they perceive as pure or unique hues. We examined the basis of these individual differences by using factor analysis to examine the variations in hue-scaling functions from both new and previously published data. Observers reported the perceived proportion of red, green, blue or yellow in chromatic stimuli sampling angles at fixed intervals within the LM and S cone-opponent plane. These proportions were converted to hue angles in a perceptual-opponent space defined by red vs. green and blue vs. yellow axes. Factors were then extracted from the correlation matrix using PCA and Varimax rotation. These analyses revealed that inter-observer differences depend on seven or more narrowly-tuned factors. Moreover, although the task required observers to decompose the stimuli into four primary colors, there was no evidence for factors corresponding to these four primaries, or for opponent relationships between primaries. Perceptions of "redness" in orange, red, and purple, for instance, involved separate factors rather than one shared process for red. This pattern was compared to factor analyses of Monte Carlo simulations of the individual differences in scaling predicted by variations in standard opponent mechanisms, such as their spectral tuning or relative sensitivity. The observed factor pattern is inconsistent with these models and thus with conventional accounts of color appearance based on the Hering primaries. Instead, our analysis points to a perceptual representation of color in terms of multiple mechanisms or decision rules that each influence the perception of only a relatively narrow range of hues, potentially consistent with a population code for color suggested by cortical physiology.
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O'Neil SF, Mac A, Rhodes G, Webster MA. Model Fitting Versus Curve Fitting: A Model of Renormalization Provides a Better Account of Age Aftereffects Than a Model of Local Repulsion. Iperception 2016; 6:2041669515613669. [PMID: 27551353 PMCID: PMC4975122 DOI: 10.1177/2041669515613669] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Recently, we proposed that the aftereffects of adapting to facial age are consistent with a renormalization of the perceived age (e.g., so that after adapting to a younger or older age, all ages appear slightly older or younger, respectively). This conclusion has been challenged by arguing that the aftereffects can also be accounted for by an alternative model based on repulsion (in which facial ages above or below the adapting age are biased away from the adaptor). However, we show here that this challenge was based on allowing the fitted functions to take on values which are implausible and incompatible across the different adapting conditions. When the fits are constrained or interpreted in terms of standard assumptions about normalization and repulsion, then the two analyses both agree in pointing to a pattern of renormalization in age aftereffects.
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Buck SL, Baraas R, Lee BB, Lindsey DT, Uchikawa K, Webster MA, Werner JS. Color vision: introduction by the feature editors. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2016; 33:CV1-CV2. [PMID: 26974947 DOI: 10.1364/josaa.33.000cv1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
This feature issue of the Journal of the Optical Society of America A (JOSA A) reflects the basic and applied research interests of members of the color vision community. Most of the articles stem from presentations at the 23rd Biennial Symposium of the International Colour Vision Society (ICVS).
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Smet KA, Webster MA, Whitehead LA. A simple principled approach for modeling and understanding uniform color metrics. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2016; 33:A319-31. [PMID: 26974939 PMCID: PMC4793282 DOI: 10.1364/josaa.33.00a319] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
An important goal in characterizing human color vision is to order color percepts in a way that captures their similarities and differences. This has resulted in the continuing evolution of "uniform color spaces," in which the distances within the space represent the perceptual differences between the stimuli. While these metrics are now very successful in predicting how color percepts are scaled, they do so in largely empirical, ad hoc ways, with limited reference to actual mechanisms of color vision. In this article our aim is to instead begin with general and plausible assumptions about color coding, and then develop a model of color appearance that explicitly incorporates them. We show that many of the features of empirically defined color order systems (those of Munsell, Pantone, NCS, and others) as well as many of the basic phenomena of color perception, emerge naturally from fairly simple principles of color information encoding in the visual system and how it can be optimized for the spectral characteristics of the environment.
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Tregillus KE, Werner JS, Webster MA. Adjusting to a sudden “aging” of the lens. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2016; 33:A129-A136. [PMID: 26924924 PMCID: PMC4765957 DOI: 10.1364/josaa.33.00a129] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Color perception is known to remain largely stable across the lifespan despite the pronounced changes in sensitivity from factors such as the progressive brunescence of the lens. However, the mechanisms and timescales controlling these compensatory adjustments are still poorly understood. In a series of experiments, we tracked adaptation in observers after introducing a sudden change in lens density by having observers wear glasses with yellow filters that approximated the average spectral transmittance of a 70-year-old lens. Individuals were young adults and wore the glasses for 5 days for 8 h per day while engaged in their normal activities. Achromatic settings were measured on a CRT before and after each daily exposure with the lenses on and off, and were preceded by 5 min of dark adaptation to control for short-term chromatic adaptation. During each day, there was a large shift in the white settings consistent with a partial compensation for the added lens density. However, there was little to no evidence of an afterimage at the end of each daily session, and participants’ perceptual nulls were roughly aligned with the nulls for short-term chromatic adaptation, suggesting a rapid renormalization when the lenses were removed. The long-term drift was also extinguished by brief exposure to a white adapting field. The results point to distinct timescales and potentially distinct mechanisms compensating for changes in the chromatic sensitivity of the observer.
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Abstract
Sensory systems continuously mold themselves to the widely varying contexts in which they must operate. Studies of these adaptations have played a long and central role in vision science. In part this is because the specific adaptations remain a powerful tool for dissecting vision, by exposing the mechanisms that are adapting. That is, "if it adapts, it's there." Many insights about vision have come from using adaptation in this way, as a method. A second important trend has been the realization that the processes of adaptation are themselves essential to how vision works, and thus are likely to operate at all levels. That is, "if it's there, it adapts." This has focused interest on the mechanisms of adaptation as the target rather than the probe. Together both approaches have led to an emerging insight of adaptation as a fundamental and ubiquitous coding strategy impacting all aspects of how we see.
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Winkler AD, Spillmann L, Werner JS, Webster MA. Asymmetries in blue-yellow color perception and in the color of 'the dress'. Curr Biol 2015; 25:R547-8. [PMID: 25981792 DOI: 10.1016/j.cub.2015.05.004] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The perception of color poses daunting challenges, because the light spectrum reaching the eye depends on both the reflectance of objects and the spectrum of the illuminating light source. Solving this problem requires sophisticated inferences about the properties of lighting and surfaces, and many striking examples of 'color constancy' illustrate how our vision compensates for variations in illumination to estimate the color of objects (for example [1-3]). We discovered a novel property of color perception and constancy, involving how we experience shades of blue versus yellow. We found that surfaces are much more likely to be perceived as white or gray when their color is varied along bluish directions, compared with equivalent variations along yellowish (or reddish or greenish) directions. This selective bias may reflect a tendency to attribute bluish tints to the illuminant rather than the object, consistent with an inference that indirect lighting from the sky and in shadows tends to be bluish. The blue-yellow asymmetry has striking effects on the appearance of images when their colors are reversed, turning white to yellow and silver to gold, and helps account for the variation among observers in the colors experienced in 'the dress' image that recently consumed the internet. Observers variously describe the dress as blue-black or white-gold, and this has been explained by whether the dress appears to be in direct lighting or shade (for example [5]). We show that these individual differences and potential lighting interpretations also depend on the special ambiguity of blue, for simply reversing the image colors causes almost all observers to report the lighter stripes as yellowish.
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Radhakrishnan A, Dorronsoro C, Sawides L, Webster MA, Marcos S. A cyclopean neural mechanism compensating for optical differences between the eyes. Curr Biol 2015; 25:R188-9. [PMID: 25734264 PMCID: PMC4354679 DOI: 10.1016/j.cub.2015.01.027] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The two eyes of an individual routinely differ in their optical and neural properties, yet percepts through either eye remain more similar than predicted by these differences. Little is known as to how the brain resolves this conflicting information. Differences in visual inputs from the two eyes have been studied extensively in the context of binocular vision and rivalry [1], but it remains unknown how the visual system calibrates and corrects for normal variability in image quality between the eyes, and whether this correction is applied to each eye separately or after their signals have converged. To test this, we used adaptive optics to control and manipulate the blur projected on each retina, and then compared judgments of image focus through either eye and how these judgments were biased by adapting to different levels of blur. Despite significant interocular differences in the magnitude of optical blur, the blur level that appeared best focused was the same through both eyes, and corresponded to the ocular blur of the less aberrated eye. Moreover, for both eyes, blur aftereffects depended on whether the adapting blur was stronger or weaker than the native blur of the better eye, with no aftereffect when the blur equaled the aberrations of the better eye. Our results indicate that the neural calibration for the perception of image focus reflects a single 'cyclopean' site that is set monocularly by the eye with better optical quality. Consequently, what people regard as 'best-focused' matches the blur encountered through the eye with better optics, even when judging the world through the eye with poorer optics.
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O'Neil SF, Mac A, Rhodes G, Webster MA. Adding years to your life (or at least looking like it): a simple normalization underlies adaptation to facial age. PLoS One 2014; 9:e116105. [PMID: 25541948 PMCID: PMC4277445 DOI: 10.1371/journal.pone.0116105] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2014] [Accepted: 12/03/2014] [Indexed: 11/18/2022] Open
Abstract
Adaptation has been widely used to probe how experience shapes the visual encoding of faces, but the pattern of perceptual changes produced by adaptation and the neural mechanisms these imply remain poorly characterized. We explored how adaptation alters the perceived age of faces, a fundamental facial attribute which can uniquely and reliably be scaled by observers. This allowed us to measure how adaptation to one age level affected the full continuum of perceived ages. Participants guessed the ages of faces ranging from 18-89, before or after adapting to a different set of faces composed of younger, older, or middle-aged adults. Adapting to young or old faces induced opposite linear shifts in perceived age that were independent of the model's age. Specifically, after adapting to younger or older faces, faces of all ages appeared 2 to 3 years older or younger, respectively. In contrast, middle-aged adaptors induced no aftereffects. This pattern suggests that adaptation leads to a simple and uniform renormalization of age perception, and is consistent with a norm-based neural code for the mechanisms mediating the perception of facial age.
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Webster MA. Probing the functions of contextual modulation by adapting images rather than observers. Vision Res 2014; 104:68-79. [PMID: 25281412 PMCID: PMC4253075 DOI: 10.1016/j.visres.2014.09.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Revised: 08/21/2014] [Accepted: 09/01/2014] [Indexed: 11/29/2022]
Abstract
Countless visual aftereffects have illustrated how visual sensitivity and perception can be biased by adaptation to the recent temporal context. This contextual modulation has been proposed to serve a variety of functions, but the actual benefits of adaptation remain uncertain. We describe an approach we have recently developed for exploring these benefits by adapting images instead of observers, to simulate how images should appear under theoretically optimal states of adaptation. This allows the long-term consequences of adaptation to be evaluated in ways that are difficult to probe by adapting observers, and provides a common framework for understanding how visual coding changes when the environment or the observer changes, or for evaluating how the effects of temporal context depend on different models of visual coding or the adaptation processes. The approach is illustrated for the specific case of adaptation to color, for which the initial neural coding and adaptation processes are relatively well understood, but can in principle be applied to examine the consequences of adaptation for any stimulus dimension. A simple calibration that adjusts each neuron's sensitivity according to the stimulus level it is exposed to is sufficient to normalize visual coding and generate a host of benefits, from increased efficiency to perceptual constancy to enhanced discrimination. This temporal normalization may also provide an important precursor for the effective operation of contextual mechanisms operating across space or feature dimensions. To the extent that the effects of adaptation can be predicted, images from new environments could be "pre-adapted" to match them to the observer, eliminating the need for observers to adapt.
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Harris JR, Lau H, Surgeoner BV, Chua N, Dobrovolsky W, Dort JC, Kalaydjian E, Nesbitt M, Scrimger RA, Seikaly H, Skarsgard D, Webster MA. Health care delivery for head-and-neck cancer patients in Alberta: a practice guideline. ACTA ACUST UNITED AC 2014; 21:e704-14. [PMID: 25302041 DOI: 10.3747/co.21.1980] [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: 02/06/2023]
Abstract
BACKGROUND The treatment of head-and-neck cancer is complex and requires the involvement of various health care professionals with a wide range of expertise. We describe the process of developing a practice guideline with recommendations about the organization and delivery of health care services for head-and-neck cancer patients in Alberta. METHODS Outcomes of interest included composition of the health care team, qualification requirements for team members, cancer centre and team member volumes, infrastructure needs, and wait times. A search for existing practice guidelines and a systematic review of the literature addressing the organization and delivery of health care services for head-and-neck cancer patients were conducted. The search included the Standards and Guidelines Evidence (sage) directory of cancer guidelines and PubMed. RESULTS One practice guideline was identified for adaptation. Three additional practice guidelines provided supplementary evidence to inform guideline recommendations. Members of the Alberta Provincial Head and Neck Tumour Team (consisting of various health professionals from across the province) provided expert feedback on the adapted recommendations through an online and in-person review process. Selected experts in head-and-neck cancer from outside the province participated in an external online review. SUMMARY The recommendations outlined in this practice guideline are based on existing guidelines that have been modified to fit the Alberta context. Although specific to Alberta, the recommendations lend credence to similar published guidelines and could be considered for use by groups lacking the resources of appointed guideline panels. The recommendations are meant to be a guide rather than a fixed protocol. The implementation of this practice guideline will depend on many factors, including but not limited to availability of trained personnel, adequate funding of infrastructure, and collaboration with other associations of health care professionals in the province.
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Buck SL, Baraas R, Bonnardel V, Lee BB, Lindsey DT, Webster MA, Werner JS. Color vision: Introduction by the feature editors. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2014; 31:CV1-CV2. [PMID: 24695210 DOI: 10.1364/josaa.31.000cv1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
This feature issue of the Journal of the Optical Society of America A (JOSA A) stems from the 22nd Biennial Symposium of the International Colour Vision Society (ICVS) and reflects the basic and applied research interests of members of the color vision community. A profile is included of the 2013 Verriest Medal recipient.
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Webster J, Kay P, Webster MA. Perceiving the average hue of color arrays. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2014; 31:A283-92. [PMID: 24695184 PMCID: PMC3979548 DOI: 10.1364/josaa.31.00a283] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
The average of a color distribution has special significance for color coding (e.g., to estimate the illuminant) but how it depends on the visual representation (e.g., perceptual versus cone-opponent) or nonlinearities (e.g., categorical coding) is unknown. We measured the perceived average of two colors shown alternated in spatial arrays. Observers adjusted the components until the average equaled a specified reference hue. Matches for red, blue-red, or yellow-green were consistent with the arithmetic mean chromaticity, while blue-green settings deviated toward blue. The settings show little evidence for categorical coding, and cannot be predicted from the scaled appearances of the individual components.
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O'Neil SF, Webster MA. Filling in, filling out, or filtering out: processes stabilizing color appearance near the center of gaze. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2014; 31:A140-A147. [PMID: 24695162 PMCID: PMC3979538 DOI: 10.1364/josaa.31.00a140] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Spectral sensitivity varies markedly across the center of gaze, in part because of the rapid decline in the density of macular pigment outside the fovea. Yet despite these retinal inhomogeneities, the color appearance of large uniform fields remains very uniform. We explored some of the processes contributing to these stable color percepts by measuring the effects of field size and eccentricity on saturated purples, whose spectra should show the largest biases with macular pigment screening. Small purple fields at 0° and 8° eccentricities differ in appearance but by much less than predicted by the macular screening or by compensation for the average effects of this screening at the two loci. This shows that the compensation is already nearly complete because of local adjustments that filter out the sensitivity variation and confirms that this filtering includes adjustments beyond average gain changes in the cones. In large fields, the appearance is dominated by the local peripheral color. This bias persists when the field edge is fixated or when abrupt edges are removed in Gaussian spots, suggesting that the spreading is not strongly dependent on luminance edges.
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Tregillus K, Webster MA. Dynamics of color contrast adaptation. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2014; 31:A314-A321. [PMID: 24695188 PMCID: PMC3979535 DOI: 10.1364/josaa.31.00a314] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Many forms of color adaptation have been found to reflect both short- and long-term adjustments. We explored the buildup and decay of adaptation to chromatic contrast (temporal modulations of color) for which the dynamics are unknown. A matching task was used to track the perceived contrast of chromatic pulses of varying physical contrast during and after adapting for 1 h to a high contrast modulation repeated over five successive days. The adaptation was characterized by rapid response changes that remained stable in both time course and form across sessions. There was no consistent evidence for long-term plasticity over the time scales we tested.
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