Beaudot W.H.A., Mullen K.T. (2001), Effect of Element Density on Contour Integration in Luminance and Color Vision, ARVO (Association for Research in Vision and Ophthalmology) Annual Meeting, Fort Lauderdale, Florida, April 29-May 4, Investigative Ophthalmology & Vision Science 42(4), S515/2773, March 2001.
EFFECT OF ELEMENT DENSITY ON CONTOUR INTEGRATION IN LUMINANCE AND COLOR VISION
((W.H.A. Beaudot, K.T. Mullen))
McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Canada.
Purpose. We previously demonstrated, using stimuli of identical density, that the blue-yellow (BY), red-green (RG) and achromatic (Ach) mechanisms perform similarly on contour integration (Mullen et al., Vis. Res. 40, 2000). However we also found that stimuli of identical physical densities are not perceived equally (Beaudot & Mullen, Perception 29, 2000): blue-yellow stimuli are perceived as significantly more dense than RG and Ach stimuli. Here we compared the effect of density on contour integration by the BY, RG, and Ach mechanisms.
Methods. The task requires the linking of orientation across space to detect a path in a stimulus composed of randomly oriented Gabors elements (1.5 cpd, sigma = 0.17 deg), measured using a temporal 2AFC method. A path of 10 elements was pasted into a 14 x 14 cells array, and background elements were randomly positioned within the available cells. Mean distance between elements varied between 2 and 3 times the wavelength of the elements (0.66 deg), and the total number of elements was fixed. Path detection was measured as a function of its curvature.
Results. We found for all curvatures that performance for the BY mechanism increases with density, while performance for the Ach mechanism is relatively independent of density.
Conclusions. This result suggests that contour integration by the BY mechanism relies more on short-range interactions than on long-range interactions in comparison to the Ach mechanism. This effect of contour integration and the enhanced perceived density of BY elements may have a common limitation in the BY system.
Research supported CIHR Grant MOP-10819