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Bruno Richard, Eva Chadnova, Daniel Baker; Dichoptic imbalance of luminance and its effects on the phase component of steady-state EEG signals. Journal of Vision 2016;16(12):431. doi: https://doi.org/10.1167/16.12.431.
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© ARVO (1962-2015); The Authors (2016-present)
A neutral density (ND) filter placed before one eye will produce a dichoptic imbalance in luminance, which attenuates responses to visual stimuli and generates a lag in neural signals from retina to cortex in the filtered eye (Wilson & Anstis, 1969, Am J Psychol, 82, 350-358). This, in turn, can induce disparity cues that lead to an illusory percept of depth (e.g., the Pulfrich effect). Here, we explored how the increased latency of the filtered eye alters neural responses to stimuli presented either monocularly or binocularly. We measured steady-state (SSVEPs) contrast response functions from the occipital pole at 6 different contrast values (0 to 96%) with 3 cycles/° sinusoidal gratings flickering at 5 Hz. To manipulate the balance of luminance between the eyes, neutral density filters (0.6, 1.2, and 1.8 ND) were placed in front of the dominant eye of observers while stimuli were presented at maximum contrast either to the filtered eye or to both eyes. The amplitude component of SSVEPs increased monotonically as a function of stimulus contrast and decreased as a function of filter strength in both monocular and binocular viewing conditions. For monocular stimuli, the ND filter increased the lag of the phase component of SSVEPs, up to a latency of 63 ms (95%CI +/- 31ms) at a filter of 1.8 ND. However, under binocular conditions, no apparent phase lag in the SSVEPs could be identified. This is indicative of a binocular combination process that suppresses the lagged input from the filtered eye. We explain these data with a computational model that implements a variable temporal impulse response function placed prior to a binocular contrast gain control mechanism, which, under binocular viewing conditions, suppresses the attenuated and lagged responses of the filtered eye. This model, additionally, offers insight on interocular interactions that may occur in amblyopia.
Meeting abstract presented at VSS 2016
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