Suppression of visible persistence as a function of spatial separation between inducing stimuli.

In the fIrst of two experiments, suppression of the visible persistence of a temporally leading stimulus by a trailing stimulus was studied as ajoint function of stimulus onset asynchrony (SOA) and of spatial proximity between the two stimuli. In agreement with earlier work, temporal integration between the two successive stimuli was progressively impaired as SOA was increased. In addition, degree of suppression of visible persistence was found to increase markedly with proximity. This confIrms the outcome of earlier research that employed trains of successive stimuli seen in apparent motion. However, the present fInding suggests that neither a seriated mode of display nor the appearance of coherent motion are necessary for the suppressive effect of spatial proximity. The results favor an account based on inhibitory interactions, rather than one based on spatiotemporal summation. Further predictions from inhibition theory-bearing on the luminance of the component stimuli-were tested and confIrmed in a second experiment.