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Abstract
UNLABELLED Saccadic eye movements direct the high-resolution foveae of our retinas toward objects of interest. With each saccade, the image jumps on the retina, causing a discontinuity in visual input. Our visual perception, however, remains stable. Philosophers and scientists over centuries have proposed that visual stability depends upon an internal neuronal signal that is a copy of the neuronal signal driving the eye movement, now referred to as a corollary discharge (CD) or efference copy. In the old world monkey, such a CD circuit for saccades has been identified extending from superior colliculus through MD thalamus to frontal cortex, but there is little evidence that this circuit actually contributes to visual perception. We tested the influence of this CD circuit on visual perception by first training macaque monkeys to report their perceived eye direction, and then reversibly inactivating the CD as it passes through the thalamus. We found that the monkey's perception changed; during CD inactivation, there was a difference between where the monkey perceived its eyes to be directed and where they were actually directed. Perception and saccade were decoupled. We established that the perceived eye direction at the end of the saccade was not derived from proprioceptive input from eye muscles, and was not altered by contextual visual information. We conclude that the CD provides internal information contributing to the brain's creation of perceived visual stability. More specifically, the CD might provide the internal saccade vector used to unite separate retinal images into a stable visual scene. SIGNIFICANCE STATEMENT Visual stability is one of the most remarkable aspects of human vision. The eyes move rapidly several times per second, displacing the retinal image each time. The brain compensates for this disruption, keeping our visual perception stable. A major hypothesis explaining this stability invokes a signal within the brain, a corollary discharge, that informs visual regions of the brain when and where the eyes are about to move. Such a corollary discharge circuit for eye movements has been identified in macaque monkey. We now show that selectively inactivating this brain circuit alters the monkey's visual perception. We conclude that this corollary discharge provides a critical signal that can be used to unite jumping retinal images into a consistent visual scene.
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McCamy MB, Collins N, Otero-Millan J, Al-Kalbani M, Macknik SL, Coakley D, Troncoso XG, Boyle G, Narayanan V, Wolf TR, Martinez-Conde S. Simultaneous recordings of ocular microtremor and microsaccades with a piezoelectric sensor and a video-oculography system. PeerJ 2013; 1:e14. [PMID: 23638348 PMCID: PMC3629042 DOI: 10.7717/peerj.14] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2012] [Accepted: 01/03/2013] [Indexed: 11/20/2022] Open
Abstract
Our eyes are in continuous motion. Even when we attempt to fix our gaze, we produce so called "fixational eye movements", which include microsaccades, drift, and ocular microtremor (OMT). Microsaccades, the largest and fastest type of fixational eye movement, shift the retinal image from several dozen to several hundred photoreceptors and have equivalent physical characteristics to saccades, only on a smaller scale (Martinez-Conde, Otero-Millan & Macknik, 2013). OMT occurs simultaneously with drift and is the smallest of the fixational eye movements (∼1 photoreceptor width, >0.5 arcmin), with dominant frequencies ranging from 70 Hz to 103 Hz (Martinez-Conde, Macknik & Hubel, 2004). Due to OMT's small amplitude and high frequency, the most accurate and stringent way to record it is the piezoelectric transduction method. Thus, OMT studies are far rarer than those focusing on microsaccades or drift. Here we conducted simultaneous recordings of OMT and microsaccades with a piezoelectric device and a commercial infrared video tracking system. We set out to determine whether OMT could help to restore perceptually faded targets during attempted fixation, and we also wondered whether the piezoelectric sensor could affect the characteristics of microsaccades. Our results showed that microsaccades, but not OMT, counteracted perceptual fading. We moreover found that the piezoelectric sensor affected microsaccades in a complex way, and that the oculomotor system adjusted to the stress brought on by the sensor by adjusting the magnitudes of microsaccades.
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Affiliation(s)
- Michael B McCamy
- Department of Neurobiology, Barrow Neurological Institute, USA.,School of Mathematical and Statistical Sciences, Arizona State University, USA
| | | | - Jorge Otero-Millan
- Department of Neurobiology, Barrow Neurological Institute, USA.,Department of Signal Theory and Communications, University of Vigo, Spain
| | | | - Stephen L Macknik
- Department of Neurosurgery, Barrow Neurological Institute, USA.,Department of Neurobiology, Barrow Neurological Institute, USA
| | - Davis Coakley
- Trinity College Dublin, Dublin 2, Ireland.,St. James's Hospital(Mercer's Institute for Research in Ageing), Ireland
| | - Xoana G Troncoso
- Department of Neurobiology, Barrow Neurological Institute, USA.,Unité de Neuroscience, Information et Complexité (CNRS-UNIC), France
| | - Gerard Boyle
- St James's Hospital(Medical Physics and Bioengineering Dept.), Ireland
| | | | - Thomas R Wolf
- Neuro-Ophthalmology Unit, Barrow Neurological Institute, USA.,Neuro-Ophthalmology Consultation: Barnett-Dulaney-Perkins Eye Center, USA
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