Receptive field focus of visual area V4 neurons determines responses to illusory surfaces

Significance Visual information is often fragmented, such as when objects block each other from view, and our brain must actively deduce missing parts of an image to perceive key features of the world. This study asks whether neurons in cortical area V4 can infer the presence of an object’s surface when visual clues are limited. Indeed, our experiments reveal that certain V4 neurons enhance their responses to an array of stimuli only when they are configured to give rise to an illusory surface. Intriguingly, this effect exhibited unexpected spatial precision relative to the inducing components of the illusion. These findings provide important clues about how the brain overcomes a fundamental challenge of vision. Illusory figures demonstrate the visual system’s ability to infer surfaces under conditions of fragmented sensory input. To investigate the role of midlevel visual area V4 in visual surface completion, we used multielectrode arrays to measure spiking responses to two types of visual stimuli: Kanizsa patterns that induce the perception of an illusory surface and physically similar control stimuli that do not. Neurons in V4 exhibited stronger and sometimes rhythmic spiking responses for the illusion-promoting configurations compared with controls. Moreover, this elevated response depended on the precise alignment of the neuron’s peak visual field sensitivity (receptive field focus) with the illusory surface itself. Neurons whose receptive field focus was over adjacent inducing elements, less than 1.5° away, did not show response enhancement to the illusion. Neither receptive field sizes nor fixational eye movements could account for this effect, which was present in both single-unit signals and multiunit activity. These results suggest that the active perceptual completion of surfaces and shapes, which is a fundamental problem in natural visual experience, draws upon the selective enhancement of activity within a distinct subpopulation of neurons in cortical area V4.