Differential visual processing for equivalent retinal information from near versus far space.

Converging evidence from animal neurophysiology and human clinical studies has suggested that visual information arising from near versus far space may be mediated predominantly by different visual subsystems in the human brain. In five experiments, healthy observers either detected or identified brief peripheral targets presented in near (peripersonal) versus far (extrapersonal) space. Apparent size (subtended visual angle) and luminance were equated to provide equivalent retinal information across near and far viewing conditions. Peripheral detection accuracy declined more rapidly with increasing target eccentricity in far viewing versus near viewing conditions. Peripheral identification accuracy under similar conditions showed no such dissociation of near versus far processing with eccentricity. These data suggest that retinal information from near versus far space may be preferentially processed by substantially different neural substrates, with active modulation of the relative contributions of involved magnocellular-dorsal and parvocellular-ventral visual pathways, depending on various potential ecological uses of the retinal information.