Brain Feature Maps Reveal Progressive Animal-Feature Representations in the Ventral Stream.

What are the fundamental units of representation in the primate visual brain? While objects have become an intuitive framework for studying neurons in many parts of cortex, it is possible that neurons follow a more expressive organizational principle, such as encoding generic features present across textures, places, and objects. In this study, we used multi-electrode arrays to record from neurons in early (V1/V2), middle (V4), and late (posterior inferotemporal cortex (PIT)) areas across the visual hierarchy, estimating the local operation of each neuron over the entire visual scene. These estimates, called "heatmaps," approximate the weight sharing operation of convolutional neural networks. We found that while populations of neurons across V1, V4, and PIT responded over the full scene, they focused on salient sub-regions within object outlines. The best captured object feature class belonged to animals, not general objects, as a trend that increased over the visual hierarchy. These results show that the monkey ventral stream is partially organized to encode local animal features over objects, even as early as primary visual cortex.