Temporal Instabilities in Amblyopic Perception: A Quantitative Approach

Abstract

The purpose of this study is to quantify the temporal characteristics of spatial misperceptions in human amblyopia. Twenty-two adult participants with strabismus, strabismic, anisometropic, or mixed amblyopia were asked to describe their subjective percept of static geometrical patterns with different spatial frequencies and shapes, as seen with their non-dominant eye. We generated digital reconstructions of their perception (static images or movies) that were subsequently validated by the subjects using consecutive matching sessions. We calculated the Shannon entropy variation in time for each recorded movie, as a measure of temporal instability. Nineteen of the 22 subjects perceived temporal instabilities that can be broadly classified in two categories. We found that the average frequency of the perceived temporal instabilities is ∼1 Hz. The stimuli with higher spatial frequencies yielded more often temporally unstable perceptions with higher frequencies. We suggest that type and amount of temporal instabilities in amblyopic vision are correlated with the etiology and spatial frequency of the stimulus.

The neural basis of spatial vision losses in the dysfunctional visual system

“…Multiple authors have written about the astonishing illusory percepts reported by amblyopes through their weak eye in normal viewing conditions of static grating stimuli 68 – 70 , which demonstrates to the investigators and the patients the underlying neuronal disruption of the visual system. Our results are in line with the above work, providing a link between the perceptual outcome, misperception, and its substrate.…”

“…There is more work to be done; for example, the centre-surround stimulus in our study is too short to change the subject’s perception of the stimulus taking place. The recent proposition of only a few categories of static grating illusory perception in the AE of amblyopes 70 opens new perspectives and possibilities to further model the underlying dynamical changes in the abnormal neuronal system. In addition, our work investigated first-order tilt illusion, but there is evidence that second-order misperception in amblyopia is also abnormal 42 , whose neurophysiological modelling should further extend our understanding of the link between perception and neural network disturbances at a higher level of sensory processing.…”

Globally Normal Bistable Motion Perception of Anisometropic Amblyopes May Profit From an Unusual Coding Mechanism

“…On the contrary, suprathreshold static grating perception is affected but in a very different manner. Amblyopes staring at images of classic square gratings perceive perceptual distortions of the stimulus that could be of static or dynamic nature (Hess et al, 1978 ; Sireteanu et al, 2008 ; Thiel and Iftime, 2016 ). Thus, the two facts that (1) our group of amblyopes perceived the 120-s moving plaids normally, with classic perceptual bistability and no reports of differences in perception between the weak and fellow eyes, and (2) amblyopes did not show an effect of contrast on the global bistability of the percept hint to a motion coding system in their visual pathway that uses dynamic visual input in a different way from neurotypical subjects.…”

“…The order of presentation was random. Because the first percept is known to always be coherent in normal-sighted observers (Hupé and Rubin, 2003 ), and amblyopes are able to demonstrate possible grating misperceptions/illusions (Hess et al, 1978 ; Hess and Bradley, 1980 ; Thompson et al, 2008 ; Thiel and Iftime, 2016 ), each observer was debriefed at the end of each 120-s trial about their first percept (coherent or not) and overall visibility of the pattern. All participants reported that they could clearly see the stimuli, a single moving plaid stimulus and two grating surfaces sliding over each other, in all conditions, even at the lowest contrast used in this study.…”

“…Such an abnormal processing causes amblyopes to see differently from neurotypical subjects in visual perception tasks; for example, amblyopes may exhibit a reduction in contrast sensitivity, stereo-acuity (3D, depth perception), or visual acuity (Bradley and Freeman, 1981 ; Levi et al, 2011 ). In contrast, suprathreshold contrast perception seems equivalent between both eyes of amblyopes (Hess and Bradley, 1980 ), while prolonged observations of static gratings by amblyopes make them report illusory static or dynamic patterns in the stimulus (Sireteanu et al, 2008 ; Thiel and Iftime, 2016 ).…”