Abstract
Purpose :
The poor vision in one eye that is the hallmark of amblyopia is presumed to have a cortical origin. Here, we simultaneously measured EEG responses and behavioral reports of perceived contrast for dichoptically-presented gratings to compare neural and behavioral measures of dichoptic contrast integration in observers with amblyopia and controls.
Methods :
Observers with amblyopia (n=13) and controls (n=15) viewed a grating flickering at 7.5 Hz. Grating contrast was dichoptically modulated over time independently in each eye (1/6 and 1/8 Hz) with occasional monocular-only blocks. Participants reported perceived contrast over time by positioning a joystick. VEP responses at 7.5 Hz were extracted from electrode Oz, and the SD of this signal was taken as a measure of neural response amplitude. Responses during monocular blocks were used to estimate an attenuation weight (k) on contrast input to the non-dominant eye. This weight was applied to the contrast input to the non-dominant eye to estimate responses during dichoptic blocks. VEP and behavioral responses during dichoptic blocks were fit with a model that predicts responses as a weighted average of the mean and the max of the attenuated contrasts to the non-dominant (ND) and dominant (D) eyes: (1-w)[(CNDk+ CD)/2] + (w)[max(CNDk, CD)].
Results :
For both VEP and behavioral responses, the non-dominant eye’s contrast signal was more attenuated (k) in amblyopia than controls (p = 0.002). Attenuation parameters for VEP and behavioral responses were significantly correlated across participants with amblyopia (r = 0.62, p = 0.024), but not controls (r = 0.18, p = 0.52). The weighted average model fits (w) indicated that the VEP signal follows the mean contrast of the two eyes (controls = 0.00, amblyopia = 0.11), while the perceived contrast follows the max (controls = 0.83, amblyopia = 0.67).
Conclusions :
After accounting for monocular attenuation, the neural response to dichoptically-modulating contrast tends to reflect the average of left and right eye contrast, whereas observers tend to report that they perceive the highest contrast presented to either eye. This suggests a significant non-linear transformation of contrast signals between early visual cortex and conscious perception. Perceptual attenuation in amblyopia was significantly predicted by VEP responses, making this a promising method for assessing populations unable to conduct psychophysical tasks.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.