From discrete elements to a perceived contour in the primary visual cortex

The neuronal mechanisms underlying perceptual grouping of discrete, similarly oriented elements are not well understood. To investigate this, we imaged population responses in V1 of monkeys trained on a contour detection task. Mapping neuronal populations processing contour/background elements in V1 enabled studying the role of two encoding mechanisms: strength of population response and synchronization. Response maps early in time showed activation patches corresponding to the contour/background individual elements. An early increased synchronization between the contour elements, accompanied by decreased synchronization between the background elements, suggested that contour integration is initiated with synchronization changes. However only response modulation at later times, defined by increased activity in the contour elements, along with suppressed activity in the background elements, enabled to visualize in single trials, a salient continuous contour segregated from a noisy background. Finally, the late modulation was correlated with psychophysical performance of contour saliency, further supporting its role in contour perception. In the second part of this talk we will demonstrate the effects of microsaccades on perceptual mechanisms in V1.