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Abstract

Recent neurophysiological data suggest that some binocular neurons are sensitive to both spatial (disparity) and temporal (motion) offsets between the two eyes. Human psychophysics was used to determine whether temporal offsets in binocular stimulus presentation increase noise in stimulus encoding, thus reducing sensitivity. Vernier acuity and stereo acuity were compared, on the assumption that temporal offsets would worsen disparity discrimination, whilst leaving Vernier acuity unaffected. The effects of temporal offsets were examined by measuring discrimination thresholds under four target presentation conditions: continuous (stimulus presented continuously to both eyes for 10 frames/100 ms); alternating (asynchronous binocular presentation for 10 frames; 5 frames per eye); blanking (synchronous binocular presentation, but alternation with a blank screen; 5 frames per eye); and half-continuous (stimulus presented to both eyes for 5 frames). Observers judged whether a target line (45 min of arc × 5 min of arc) was left/right or in-front/behind the fixation cross. Sensitivity (the slope of the psychometric function) was affected by experimental condition, with best performance obtained under continuous presentation. However, no differences were evident between the other three conditions. Further, the pattern of results was the same for Vernier and stereo acuity, suggesting that these results reflect the contrast reduction of temporally interleaved stimuli, rather than effects of temporal offsets per se.