Difference in the representation of cardinal and oblique contours in cat visual cortex

Optical imaging based on intrinsic signals was used to analyze the structure of orientation column in area 18 of cat visual cortex. Recordings were obtained in 12 adult cats during presentation of contours in various orientations. In order to quantitatively evaluate the size of the response area, a method combining both information on the amplitude of the changes and the statistical significance of the changes was proposed. The results showed that the proportion of the cortical area activated reached a peak during the presentation of horizontal or vertical contours, whereas the areas activated by oblique contours were relatively smaller. Cardinal contours (0 degrees and 90 degrees ) activated 50.63 +/- 1.88% (mean +/- SE) of the cortical area in the recording site, whereas oblique contours (45 degrees and 135 degrees ) activated only 45.25 +/- 2.02% of the area. This difference in area was statistically significant (t = 2.38, d.f. = 11, and P < 0.05). The results demonstrated a difference in the representations of the cardinal and oblique contours in area 18 of the cat visual cortex.