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Updated: Sep 28, 2025

Investigating Object Representations in the Macaque Dorsal Visual Stream Using Single-unit Recordings
Published on: August 1, 2018
Orientation anisotropies in macaque visual areas
Chen Fang1, Xingya Cai1, Haidong D Lu1
1State Key Laboratory of Cognitive Neuroscience and Learning, IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing 100875, China.
Abstract:
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.
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