Surround modulation in cortical orientation map revealed by optical imaging and its dependency on receptive field eccentricity

Optical imaging was used to investigate the difference in surround modulation on orientation map related to receptive field eccentricity in cat visual cortex. Presentation of center–surround stimuli at the center of gaze resulted in no clear surround modulation; however, significant modulation was observed in its corresponding cortical area when the center–surround stimuli were presented at 10° eccentricity in more peripheral parts of the visual field. Modulation was observed both in the response magnitude and in the spatial pattern of the response. Surround orientation perpendicular to the orientation of a center patch grating showed the largest modulation in the response magnitude. The modulation became weaker as the orientation difference between the center and surround gratings became smaller. Regardless of the orientations for the central patch gratings, a similar response spatial pattern was observed in the cortical region where the underlying cells had their receptive fields covering the central patch, if the stimuli were with the same surround gratings. These properties support the notion of a relative specialization for visual information processing in peripheral representations of cortical areas.