Transfer of long-range interaction across the visual hemifield by reversed visual input

Abstract

The reversal of the retinal image using prism spectacles induces disruption of sensory-motor coordination. Although several studies report that harmonious visuomotor behavior is recovered after prism adaptation, the mechanism involved in the adaptation is largely unknown. Here we study large-scale visual plasticity between left and right hemifields using Gabor patches and left-right reversed prisms. Experiments were carried out for 5 days. Before the prism adaptation, the long-range interaction was achieved by a temporal cueing method. Temporally primed visual signals (peripheral crosses at 7.2 deg., duration=100ms) preceded vertically collinear 3 Gabors by 300–600ms. The Gabor stimuli (sigma=lambda=0.2 deg., 100ms) were presented binocularly at 3 deg. leftward from the central fixation spot. The flanker (C=0.4)-to-target distance was 6 lambda. The practice with temporal cues for 30min generated extended long-range facilitation to 9–12 lambda over days (threshold reduction=0.23±0.08 log units; 5 subjects). Before the adaptation, no transfer was observed at the opposite visual field. After two days of adaptation, the extended long-range facilitation was found not only at the practiced visual field but also at the opposite side (distance=3 deg., 0.14±0.05 log units, 2 subjects). This transfer persisted over the subsequent 3 days of adaptation and preserved after putting off the prisms. No transfer was found using up-down reversed prisms (1 subject). Control observers without prisms (2 subjects) showed no transfer. The transfer of the long-range interaction across the hemifield by prism adaptation demonstrates large-scale plasticity in early visual system induced by reversed retinotopic input. There is no commissural connection in V1 between the practiced area (left visual field) and the tested area (right visual field), thus the results suggest that the learning effect transferred through higher cortices (i.e. the parietal cortex) and projected backward to V1 during the adaptation.