From stuff to things: Responses of neurons in macaque V4 to textures and objects

Abstract

Humans and monkeys can rapidly recognize objects in everyday scenes. It is not fully understood where this computation arises, but previous work suggests selectivity for object shape first emerges in cortical area V4. To explore the mechanisms of this selectivity, we generated images on a continuum between "scrambled" textures and photographic images, preserving the local statistics of the original image while discarding structural information about scene and shape. We defined this continuum by the size of the region in which statistics were measured ("pooling region"). On average, neurons responded equally to photographic images and their scrambled counterparts. However, neurons exhibited a greater dynamic range of response to photographs. As a result, neuronal populations in V4 could more reliably discriminate between photographs than between scrambled images. Responses to partially scrambled images were more similar to responses to fully scrambled images than to photographs, even for perceptually subtle changes, and only began to resemble responses to photographs for pooling regions roughly half the size of typical V4 receptive fields. These same patterns emerged in an image similarity metric designed to predict human judgements of image degradation. Finally, V4 object selectivity showed dynamics that grew slowly and persisted following response offset, suggesting this signal may arise from recurrent mechanisms. Significance StatementObject recognition is a primary goal of visual processing, but is too complex to be computed by early visual areas. To evaluate where object-selective signals emerge, we recorded the responses of individual neurons in mid-level area V4 as macaque monkeys viewed images of objects ("things") and of matched textures ("stuff"). Object selective V4 responses emerged in two phases. Short-latency responses discriminate objects from one another, but the distinction between objects and textures arrived later. This late-emerging signal was sensitive even to small image degradations, as is human perception. Our results show how V4 initiates the brains representation of visual objects.