Temporal facilitation in the integration of contours

Abstract

Motion can be a rich source of information for the contour completion of objects that are partially occluded. In the particular case of spatiotemporal boundary formation (SBF), motion is critical for the perception of contours. This means that the system integrates the image fragments that appear along the movement over time. This process would require, in addition to the mechanisms of spatial contour integration, a process capable to accumulate the information over time. Such process could be instantiated neurally by a temporal facilitation mechanism. In this study, we investigate the plausibility of such a mechanism by mean of a psychophysical study. Using a masking/facilitation paradigm, we studied the interaction between two stimuli (mask and target) of the same orientation, located adjacent one respect to the other (0 deg), and with angles of 45 and 90 deg between them, as a function of the delay between the presentation of the target respect to the mask. An angle of 90 deg between the patches corresponds to collinearity. The stimuli were Gabor patches with a spatial frequency of 6 c/deg. The separation between patches was 3 wavelenghts. Three observers participated in the experiment. We used a 2AFC method to measure the threshold elevation of the target in presence of the mask, respect to the threshold obtained without mask. Results show that for 0 and 45 deg, the time course of facilitation, defined as a negative threshold elevation, has peaks around 25 ms for 0 deg, and 35 ms for 45 deg. For 90 deg, the maximum facilitation occurs when mask and target are presented simultaneously and decreases with increasing delay. The peaks of facilitation found for 0 and 45 deg resembles a spatiotamporal correlator that may account for a mechanism that integrates temporally signals that occur along the object motion path. Meeting abstract presented at VSS 2013