THE EFFECTS OF SPATIOTEMPORAL INTEGRATION ON MAXIMUM DISPLACEMENT THRESHOLDS FOR THE DETECTION OF COHERENT MOTION

In a series of nine experiments, observers were required to identify t he shapes of moving targets, and to discriminate regions of motion fro m regions of uncorrelated noise, Maximum displacement thresholds (D-ma x) for performing these tasks were obtained under a wide variety of co nditions, The stimulus parameters manipulated included the number of d istinct frames in the motion sequences, the stimulus onset asynchrony between each frame, the size of the moving dots, and the shape, area a nd eccentricity of the target regions, For two-frame displays presente d in alternation, the area of the target region was the only one of th ese variables to have any significant effect on D-max. For longer leng th sequences, in contrast, D-max varied dramatically among the differe nt conditions over a range of 10 min are to 10 deg, In an effort to is olate the specific processes of spatiotemporal integration, we also ex amined how performance is affected by having overlapping transparent m otions in opposite directions, or by the presence of dynamic noise or limited dot lifetimes within the moving target regions, The overall pa ttern of results suggest that D-max is primarily determined by the abi lity of the visual system to isolate motion signals from the noise pro duced by spurious false target correlations, As a general rule, D-max will increase as a result of any stimulus manipulation that increases the number of local signal correlations detected relative to those ari sing from noise, and vice versa.