Enhancement of oblique effect in the cat's primary visual cortex via orientation preference shifting induced by excitatory feedback from higher-order cortical area 21a

It is often suggested that the oblique effect, the well-known phenomenon whereby both humans and animals are visually more sensitive to vertical and horizontal contours than to oblique ones, is due to the overrepresentation of cardinal orientations in the visual cortex. The functional role of feedback projections from higher-order cortical areas to lower-order areas is not fully understood. Combining the two issues in a study using optical imaging here, we report that the neural oblique effect was significantly enhanced (3.7 times higher than the normal) in the cat's primary visual cortex through orientation shifting induced by excitatory feedback from the higher-order cortical area 21a. This suggests that a reciprocal co-excitatory mechanism may underlie the perceptual oblique effect.