Psychophysical evidence of cortical dynamics in contour integration
W H A Beaudot, R F Hess, K T Mullen
(McGill Vision Research, 687 Pine Avenue West, H4-14, Montreal, H3A 1A1, Canada; email: ;
WWW: http://wbeaudot.kybervision.net)
We determined the effect of element separation on the dynamics of contour integration. The task requires the linking of orientation across space to detect a path, measured using a temporal 2AFC method of constant stimuli. Gabor patches (1.5cpd, sigma=lambda/4) were randomly positioned within a 10x10 square grid with typically 10 elements forming a path. A stimulus cycle consists in a path or no-path stimulus followed by a masking stimulus with random orientation of its individual elements. The path and no-path stimuli were presented cyclically for 1s modulated by a temporal Gaussian window. We measured the effect of the temporal orientation modulation of the individual elements as a function of temporal frequency (1-38Hz), curvature (0-30deg) and element separation (2-5xlambda). Our results reveal that the temporal resolution of contour integration: 1) decreases with the element separation; 2) decreases with path curvature at all element separations; and 3) is better for long straight paths (10 elements) than for short straight paths (5 elements) or closed paths, with the largest difference at the shortest element separation. These findings extend our previous results (Hess, Beaudot and Mullen, 2001 Vision Research41 1023 - 1037; Beaudot and Mullen, 2001 Perception30 833 - 853) on the curvature-dependent dynamics of contour integration, and bring new insights of the involvement of feedforward, intracortical and interareal feedback processing in contour integration.
Research supported by CIHR Grants MOP-10818 and MOP-10819