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Abstract:
We have previously reported experience-dependent changes in V4 neural activity to natural images using a noise-interpolation paradigm (Rainer Logothetis, Soc Neuro Abstr 27: 399.1, 2001). To gain further insight into how responses of single V4 neurons are modified by experience, we examined activity to familiar and novel full color natural images as a function of contrast and color composition. For contrast variation, neural responses were assessed during performance of a delayed-matching-to-sample task with samples presented at different contrast levels (full, 75, 50, 25, 10, 5). In addition, responses to natural images and the luminance and chrominance components of these images alone were collected during fixation. All images were 10°×10° in size and presented at the center of gaze for a period of 300ms. We have preliminary data from 91 V4 neurons. Both contrast and color data from V4 neurons showed systematic variation as a function of stimulus familiarity. At full contrast, familiarity was reflected in reduced average population activity during the sustained portion of the visual response (from about 150ms after sample onset onwards). This difference was specific to full contrast stimuli and disappeared with decreasing contrast, because average activity to novel images decreased while activity to familiar objects slightly increased. The experiment with colored images revealed an interaction between familiarity and luminance/chrominance during the sustained visual response. Together, these studies shed further light on experience-dependent neural activity changes in the cortex of awake behaving primates.
