Seeing Differently in Near and Far: For Detection but Not Identification of Peripheral Targets

Do human observers process the same retinal information differently when it comes from near versus far space? Based on neurophysiological and neuropsychological evidence researchers have proposed that visual information for near space (peripersonal, within arm's reach) and far space (extrapersonal, beyond arm's reach) is mediated predominantly by dorsal and ventral visual pathways respectively. Here we provide behavioural evidence showing that neurologically normal human observers perceive visual information in near and far space differently when the visual stimuli in both viewing conditions subtended an equal visual angle and had equal luminance. Specifically, in tasks requiring participants to detect a briefly presented target appearing at one of many possible peripheral locations on a screen, under far viewing-distance conditions, visual accuracy declined more steeply as the eccentricity of the peripheral target increased compared to near viewing-distance conditions. This near-far difference in the slopes of the accuracy-eccentricity curve was not, however, observed for visual identification tasks using the same stimulus configuration. This remarkable near/far influence on perceptual behavior observed here suggests that the brain can actively modulate the information processing in different neural streams based on the target distance information, and consequently facilitate the ecological use of the retinal information.