Attentional limitations in the sensing of motion direction

Attentional constraints in the perceptual analysis of motion direction were exam-ined using two independent paradigms: redundant target visual search and the analy-sis of fluctuations in discrimination accuracy at threshold. Results from both meth-ods implied that directions of object motion are analyzed in parallel when those motions are translations, independent of the observer’s line of sight. The registration of rotation direction appears to be subject to a qualitatively different protocol, one that is highly capacity limited and serial-like. These results suggest that scene-based descriptions, as opposed to image-based descriptions of motion, mediate the alloca-tion of attention. ª 2001 Academic Press Motion occupies a privileged position among perceptual attributes by vir-tue of the sensitivities that humans and other mammals have for optic flow. Optic flow patterns are not typically processed in local bits and pieces, but rather are subject to a massively parallel reduction that leads to a number of important computational achievements. Parallelism in motion analysis allows animals to steer themselves, it permits the acquisition of depth infor-mation from motion parallax, it supports motion camouflage breaking, and it makes the tracking of moving objects a fairly effortless exercise in most circumstances. The mammalian visual system is evidently exquisitely at-tuned to motion and this observation has naturally led to more general inquir-ies into the logic of motion analysis, its realization in neural tissue, and to more complete inventories of the psychophysics of detection and discrimina