Representation of Cardinal Contour Overlaps Less With Representation of Nearby Angles in Cat Visual Cortex

Extensive attempts have been made to explain the neurobiological basis of the greater sensitivity of the visual system to vertically or horizontally oriented information than to information presented at oblique angles. However, investigators have largely ignored the overlap of the representation of a given angle with the representation of nearby angles. Recordings based on intrinsic optical signals were obtained in area 17 from 12 adult cats during the presentation of contours in various orientations. A method investigating both amplitude and statistical significance of changes was proposed to evaluate the orientation tuning properties for cell populations in the central area retinotopically corresponding to 0–15° of visual field. Cardinal orientations were found to activate significantly greater areas in the exposed cortical area than the areas activated by oblique orientations. Areas activated by cardinal or oblique contours and those separated from them by 10° were compared. A significantly lower degre...