A new VEP system for studying binocular single vision in human infants

Visual evoked potentials (VEPs), that provide unequivocal objective evidence of cortical binocularity have been recorded from adults and young infants using a new VEP system developed for this purpose. The system uses alternating field stereoscopy (AFS) to present separate visual stimuli to each eye. With this system, the binocular image pairs to the right and left eyes alternate at a high rate on a single video monitor. The subject wears spectacles incorporating light-scattering liquid crystal lenses which alternate electronically between opaque and clear modes in synchrony with the video monitor. To detect cortical binocularity, the system analyzes VEP activity mathematically and identifies significant responses at test frequencies reflecting binocular cortical interactions exclusively. Three types of binocular stimuli were presented: (1) dynamic random dot correlograms (correlograms); (2) dynamic random dot stereograms (stereograms); and (3) dichoptic checkerboard stimuli. The correlograms are generated when moving random dot patterns presented to each eye alternate between two phases, correlated and anticorrelated. With the stereograms, portions of random dot patterns presented to each eye are shifted horizontally relative to each other at a fixed rate, alternately producing crossed and uncrossed binocular disparities. Subjectively, these patterns appear to shift in depth. Dichoptic checkerboard stimuli are regular checkerboard patterns which reverse at different rates (frequencies) for each eye. Binocular VEPs are generated due to cortical interactions at the difference (beat) frequency. Using this VEP system, we have recorded binocular VEPs from 10 normal adults and more than 40 infant subjects.(ABSTRACT TRUNCATED AT 250 WORDS)