Neural correlates of visual spatial selective attention are altered at early and late processing stages in human amblyopia

Amblyopia is a neurodevelopmental visual disorder which results in reduced visual acuity in one eye and impaired binocular interactions. Previous studies suggest attentional deficits in amblyopic individuals. However, spatial cues which orient attention to a visual field improved performance. Here, we investigate the neural correlates of auditory-visual spatial selective attention in amblyopia during EEG recording. An auditory cue, that was followed by the presentation of two Gabor patches presented in the lower left and right visual fields, indicated the most likely location of an upcoming target Gabor. The target Gabor differed in orientation from the more frequently presented non-target Gabor patches. Adults with amblyopia and neurotypical observers were asked to detect the target Gabor monocularly at the cued location, while withholding their response to targets presented at the uncued location and to all non-target Gabor patches. Higher response rates were observed for cued compared to uncued targets in both groups. However, amblyopic individuals detected targets less efficiently with their amblyopic eye as compared to their fellow eye. Correspondingly, event-related potentials (ERPs) recorded to the onset of the non-target Gabor patches were delayed at early processing stages (150-300 ms: posterior N100) and reduced in amplitude at later time windows (150-350 ms: P200, 300-500 ms: sustained activity) in the amblyopic eye compared to the fellow eye. Such interocular differences were not observed in neurotypical observers. These findings suggest that neural resources allocated to the early formation of visual discrimination as well as later stimulus recognition processes are altered in the amblyopic eye.