Beaudot W.H.A., Mullen K.T. (1999), Temporal properties of contour integration in colour vision, ARVO (Association for Research in Vision and Ophthalmology) Annual Meeting, Fort Lauderdale, Florida, May 10-15, Investigative Ophthalmology & Vision Science 40(4), S809/4264, March 1999.
Full paper published as:
Beaudot W.H.A., Mullen K.T. (2001), Processing time of contour integration: The role of color, contrast and curvature, Perception 30(6):833-853, July 2001 .
TEMPORAL PROPERTIES OF CONTOUR INTEGRATION IN COLOUR VISION
((W.H.A. Beaudot, K.T. Mullen)) McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Canada.
Purpose. To compare the temporal properties of the red-green (RG), blue-yellow (BY) and achromatic (ACH) mechanisms in a contour integration task.
Methods. The task requires the linking of orientation across space to detect a "path". Stimuli were arrays of oriented Gabor patches (1.5 cpd, s = 0.17 deg) randomly positioned within a 14 x 14 square grid subtending 14 deg. Half the stimuli contain 10 adjacent elements aligned along a path, and the other half have no path. Reaction times were obtained for simple detection of the stimulus regardless of the presence of a path, and for path detection measured using a yes/no procedure with path and no-path stimuli randomly presented. Processing time for contour integration was calculated as the difference between simple stimulus detection and path detection, and was measured as a function of stimulus contrast and path curvature (the orientation difference between adjacent path elements).
Results. 1) Although showing significant absolute differences in reaction time, all mechanisms at all curvatures show an initial decrease in processing time with increasing contrast, followed by constant processing time at suprathreshold contrasts. 2) For straight paths processing time is longer for chromatic paths (at around 200ms) than for achromatic ones (at around 100ms). For curved paths (20 degs of curvature) processing time increases by around 100ms for ACH paths and around 50ms for colour paths. 3) Detection of the absence of path requires 50 to 100 ms of additional time independent of chromaticity, contrast and path curvature.
Conclusions. The ACH mechanism requires less processing time for contour integration than the chromatic mechanisms. The RG and BY mechanisms show no difference in processing time, although they are different in reaction time. Processing time for the ACH mechanism is, however, more dependent on path curvature than for chromatic mechanisms. On the basis of similar spatial properties, we have proposed that the three mechanisms share common contour integration process (Beaudot & Mullen, ARVO, 1998). The temporal properties of this process differ according to its chromatic inputs.