DIRECTION DISCRIMINATION OF CYCLOPEAN (STEREOSCOPIC) AND LUMINANCE MOTION

This study compared direction discrimination of cyclopean (stereoscopi c) and luminance motion involving stimuli equated for effective streng th, The stimuli were random-walk cinematogram (RWC) displays whose sig nal and noise discs were created from binocular disparity differences embedded in a dynamic random-dot stereogram or from luminance differen ces, Experiment 1 measured global motion detection thresholds for cycl opean and luminance stimuli by manipulating the proportion of signal t o noise discs, Detection thresholds fbr cyclopean motion were about 25 % whereas detection thresholds for luminance motion were 5%, thus five times more cyclopean motion events than luminance events were necessa ry to elicit threshold responding. Experiment 2 measured thresholds fo r discriminating the direction of cyclopean and luminance motion under conditions of equal stimulus strength by presenting the motion displa ys at equal multiples of detection threshold. Direction discrimination thresholds (ranging from about 5-30 deg, depending upon conditions) w ere similar for cyclopean and luminance motion, thus the precision wit h which the pooling of local motion events in one direction can be dis criminated from the pooling of events in a slightly different directio n is the same for cyclopean and luminance stimuli, The finding that cy clopean motion information is pooled is consistent with the idea that the direction of cyclopean motion is coded in the responses of a popul ation of directionally selective mechanisms. (C) 1997 Elsevier Science Ltd.