Orientation anisotropies in macaque visual areas

In mammals, a larger number of neurons in V1 are devoted to cardinal (horizontal and vertical) orientations than to oblique orientations. However, electrophysiological results from the macaque monkey visual cortex are controversial. Both isotropic and anisotropic orientation distributions have been reported. It is also unclear whether different visual areas along the visual hierarchy have different orientation anisotropies. We analyzed orientation maps in a large set of intrinsic signal optical imaging data and found that both V1 and V4 exhibited significant orientation anisotropies. However, their overrepresented orientations were very different: in V1, both cardinal and radial orientations were overrepresented, while in V4, only cardinal bias was presented. These findings suggest that different cortical areas have evolved to emphasize different features that are suitable for their functional purposes, a factor that needs to be considered when efforts are made to explain the relationships between the visual environment and the cortical representation and between the cortical representation and visual perception.

Automated summary

In mammals, there is a higher number of neurons in the V1 area dedicated to cardinal orientations than to oblique orientations. However, studies on macaque monkeys have produced conflicting results regarding the orientation distribution in their visual cortex. It has also been unclear whether different visual areas in the cortex exhibit different orientation anisotropies. This study analyzed optical imaging data and found that both V1 and V4 exhibit significant orientation anisotropies, but with different overrepresented orientations. These findings suggest that different cortical areas have evolved to prioritize different features for their functional purposes.