Damage to the primary visual cortex typically causes cortical blindness (CB) in the hemifield contralateral to the damaged hemisphere. Recent evidence indicates that visual training can partially reverse CB at trained locations. Whereas training induces near-complete recovery of coarse direction and orientation discriminations, deficits in fine motion processing remain. Here, we systematically disentangle components of the perceptual inefficiencies present in CB fields before and after coarse direction discrimination training. In seven human CB subjects, we measured threshold versus noise functions before and after coarse direction discrimination training in the blind field and at corresponding intact field locations. Threshold versus noise functions were analyzed within the framework of the linear amplifier model and the perceptual template model. Linear amplifier model analysis identified internal noise as a key factor differentiating motion processing across the tested areas, with visual training reducing internal noise in the blind field. Differences in internal noise also explained residual perceptual deficits at retrained locations. These findings were confirmed with perceptual template model analysis, which further revealed that the major residual deficits between retrained and intact field locations could be explained by differences in internal additive noise. There were no significant differences in multiplicative noise or the ability to process external noise. Together, these results highlight the critical role of altered internal noise processing in mediating training-induced visual recovery in CB fields, and may explain residual perceptual deficits relative to intact regions of the visual field.
Bibliographical noteFunding Information:
We thank Terrance Schaefer for performing Humphrey visual field tests on all the patients, and Jared Abrams for his comments on a previous version of this manuscript. This work was supported by grants from the National Institute of Health (EY021209 to KRH, EY016200 to MC, and EY019295 to DT; Core Center Grant P30 EY001319 to the Center for Visual Science; and by training grant T32 EY007125 to the Center for Visual Science), by a Collaborative Grant from the Schmitt Program on Integrative Brain Research (to KRH), and by an unrestricted grant from the Research to Prevent Blindness Foundation to the Flaum Eye Institute. KRH is a Research to Prevent Blindness Lew R. Wasserman Merit Award recipient.