Fixational eye movements, natural image statistics, and fine spatial vision

Perception and motor control are often regarded as two separate branches of neuroscience. Like most species, however, humans are not passively exposed to the incoming flow of sensory data, but actively seek useful information. By shaping input signals in ways that simplify perceptual tasks, behavior might play an important role in establishing efficient sensory representations in the brain. Under natural viewing conditions, the main source of motion of the stimulus on the retina is not the scene but our own behavior. The retinal image is never still, even during visual fixation, when small eye movements combine with movements of the head and body to continually perturb the location of gaze. This article examines the impact of the fixational motion of the retinal image on the statistics of visual input and the neural encoding of visual information. Building upon recent theoretical and experimental results, it is argued that an unstable fixation constitutes an efficient strategy for acquiring information from natural scenes. According to this theory, the fluctuations of luminance caused by the incessant motion of the eye equalize the power present at different spatial frequencies in the spatiotemporal stimulus on the retina. This phenomenon yields compact neural representations, emphasizes fine spatial detail, and might enable a temporal multiplexing of visual information from the retina to the cortex. This theory posits motor contributions to early visual representations and suggests that perception and behavior are more intimately tied than commonly thought.