Intact Perceptual Interactions of Interocular Temporal Phase and Contrast Disparities in Amblyopia

Abstract

Purpose: Interocular temporal and contrast differences have been applied separately to improve binocular integration and treat amblyopia. However, the extent to which binocular integration in amblyopia can be improved by combining interocular differences in timing and contrast has yet to be tested. We evaluated how these parameters interact in individuals with amblyopia and in normally sighted controls.

Methods: We developed an interocular flicker integration task in which a pair of dichoptic gratings flickered sinusoidally in counterphase (2 hertz [Hz], 90-degree spatial and temporal offset), producing the appearance of motion. We determined the interocular delay required for optimal integration by adding phase delays to the 90-degree phase offset (left or right eye leading, −80 degrees to +80 degrees). Delays were tested across different interocular contrast conditions: 50%-50%, 70%-30%, or 85%-15%. Amblyopic (n = 12) and control (n = 12) participants reported the perceived motion direction.

Results: Both groups showed broad temporal tuning of flicker integration. Accuracy in the contrast-balanced condition was highest with no added phase delay, and Gaussian fits to the data showed peak performance at a negligible delay (−0.3 degrees). Across both groups, an 85%-15% contrast disparity reduced overall accuracy and shifted peak accuracy to a delay of 28.6 degrees in the higher contrast eye.

Conclusions: Our data demonstrate that interocular temporal and contrast disparities interact similarly in normally sighted individuals and those with amblyopia. In this task, temporal delays and contrast imbalance manipulations interact predictably, such that the effects of imbalanced contrast are counteracted by a leading temporal offset for the eye with the lower contrast stimulus.