Abstract
Most studies of neuronal responses in amblyopia have focused on primary visual cortex (V1) in anesthetized animals. Typically these experiments reveal decreased binocularity, and reduced contrast sensitivity and visual resolution in cells driven by the amblyopic eye (AE) compared to the fellow eye (FE). These neuronal deficits are less marked than behaviorally measured visual losses, implying that there are deficits in visual processing downstream of V1. Amblyopes are also impaired on complex tasks such as form discrimination that are thought to rely on extrastriate visual areas. We have therefore studied correlates of visual sensitivity and form discrimination in recordings from an awake, fixating macaque made amblyopic by early surgical esotropia. We recorded multiunit activity from two 96-channel Utah arrays, one along the V1/V2 border and one in V4. We briefly flashed a variety of stimuli onto the multiunit receptive fields, including sinusoidal gratings and radially modulated shapes. FE sites were generally more responsive than AE sites in V1, V2, and V4. Activity at many sites was binocular, but dominated by the FE. Monocular sites were usually driven by the FE. In V4, which in normal monkeys is wholly binocular, almost half of recording sites were monocular. In V1 and V2, high spatial frequencies evoked stronger responses in the FE than in the AE, but radial forms drove inconsistent activity. In contrast, most V4 sites were not tuned for spatial frequency, but many responded vigorously to radial forms. Most of these form-responsive sites responded exclusively or more strongly to the FE. This strongly FE-biased representation of form responses in V4 is consistent with the idea that changes in that area are related to the substantial deficits in form perception shown by many amblyopes (including the monkey subject of these experiments).
Meeting abstract presented at VSS 2018