The visual system makes sophisticated use of contextual information for segregation and grouping operations that identify objects and place them against their background. Recent work in a number of laboratories has indicated that the responses of single cells in striate cortex are highly context dependent, as are perceptual judgments. The present proposal is motivated by our recent findings of context-dependent responses in the human VEP that appear to parallel those seen in psychophysics. These spatial integration mechanisms are degraded by abnormal visual experience during the critical period of visual development which results in amblyopia. Current computational models have yet to consider the role of spatial interactions between local filter mechanisms that our new findings indicate are needed for a valid account of the amblyopic deficit. Accurate computational models will also require a great deal more information regarding the """"""""functional connectivity"""""""" of the visual field. The proposed experiments are designed to obtain such information in normal adults, to determine how this information is elaborated during the course of postnatal development in normal infants and to determine how it is disrupted in amblyopia. The experiments will utilize a combination of VEP and psychophysical methods to identify different mechanisms of lateral interaction and to characterize their stimulus dependencies along the dimensions of orientation, direction, spatial phase and separation. Lateral interactions will be characterized by frequency domain non-linear analysis techniques that make use of a newly developed, high-resolution signal processing method. In pursuit of these goals, we will have developed VEP methods for measuring lateral interaction that are likely to be more sensitive than conventional measures of grating acuity or contrast sensitivity. These methods could be applied in future clinical studies of human amblyopia and strabismus pathophysiology and possibly even to individual patient management.
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