Categorical and coordinate spatial processing: More on contributions of the transient/magnocellular visual system

Observers were presented with stimuli consisting of a line and two horizont ally separated dots. A categorical spatial task required observers to indic ate whether the dots were above or below the line and a coordinate spatial task required observers to indicate whether the line could tit into the spa ce between the two dots. Coordinate (bur nor categorical) spatial processin g was less accurate and tool; longer with stimuli presented on a red backgr ound than with stimuli presented on a green background. even though the bac kground color varied ran randomly from trial to trial and the viewing scree n remained gray between trials. Because the color red attenuates processing in the transient/magnocellular visual system, these results suggest that c oordinate spatial processing is dependent on that pathway. Furthermore, suc h effects do not involve mechanisms of perceptual adaptation that depend on the same color background being present throughout an experiment or for a prolonged period of time. As in earlier experiments, the effects of color c ondition were the same regardless of which visual field land hemisphere) re ceived the stimulus information. However, in contrast ro the results of ear lier experiments, there was no significant interaction of task and visual f ield. (C) 2001 Academic Press.