Abstract
Our previous study reported that attentional modulation in the visual cortex from input of the amblyopic eye is substantially reduced in adults with strabismic amblyopia, suggesting that interocular attention asymmetry (bias) may play a role in amblyopic suppression (Hou et al., 2016). In this study, we measured selective attention allocation from each eye of adults with anisometropic and strabismic amblyopia by using dichoptic attention stimuli that induce interocular suppression. Specifically, the dichoptic stimuli consisted of highly visible targets (i.e., vertical Gabors with 2 cpd spatial frequency at ≥ 25% contrast) displayed in the tested eye, while distractors (i.e., horizontal Gabors) were simultaneously displayed in the non-tested eye. A 500 ms-valid attentive cue preceded each trial indicating which eye would get the targets. The task was to quickly search for and count the targets among distractors through a mirror stereoscope. The targets were arranged at 50% probability in each eye in a random order within a block. Interocular contrast difference was neutralized by increasing contrast to the stimuli of the amblyopic eye to allow equal-perceptual visibilities between the eyes. Our results showed that the searching and counting performances in the amblyopic eye of individuals with anisometropic and strabismic amblyopia were significantly worse compared to those in their non-amblyopic fellow eye and normal vision eyes, suggesting selective attention deficits in the amblyopic eye under experimental environment of interocular suppression. The performances in the fellow eye of strabismic individuals were also worse compared to those in the eyes of normal-vision controls. Interocular attention bias was computed as the difference in performance between dom/fellow and non-dom/amblyopic eye conditions. Our data revealed that there was no attention bias between the eyes in normal vision; however, selective visual attention was biased toward the fellow eye in both types of amblyopia.