Beaudot W.H.A., Mullen K.T. (1998), Role of the blue-yellow mechanism in contour integration, ARVO (Association for Research in Vision and Ophthalmology) Annual Meeting, Fort Lauderdale, Florida, May 10-15, Investigative Ophthalmology & Vision Science 39(4), S848/3938, March 1998.
ROLE OF THE BLUE-YELLOW MECHANISM IN CONTOUR INTEGRATION
((W.H.A. Beaudot, K.T. Mullen)) McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Canada.
Purpose. To compare the performance of the blue-yellow mechanism with the red-green and achromatic mechanisms in a contour integration task in the fovea and parafovea (0-5 deg).
Methods. The task requires the linking of orientation across space: stimuli were arrays of oriented band-pass elements (Gabor patches of 1.5 cpd with s = 0.17 deg) randomly positioned in a 14 x 14 grid (subtending 14 deg of visual angle), in which 10 adjacent elements were aligned along a path (McIlhagga & Mullen, Vis. Res. 36, 1996). Detection of the path was measured using a 2AFC procedure as a function of stimulus contrast, path angle (the orientation difference between adjacent path elements) and eccentricity. Stimuli were represented within a 3D cone contrast space.
Results. 1) The blue-yellow (BY), like the red-green (RG) and achromatic (ACH) mechanisms, can support a path integration task. 2) The BY mechanism shows a less steep decline in contour integration across the parafovea than the RG mechanism, whereas the ACH mechanism shows virtually no loss of contour integration. 3) Across the central 5 degrees, the BY mechanism has a poorer orientation discrimination of individual path elements than the other two mechanisms at path detection threshold. However, 4) the BY, RG and ACH mechanisms all show a similar dependence on path angle, and 5) all show a similar decline in the presence of orientation noise.
Conclusions. Despite the "front-end" differences of the BY mechanism in terms of cone and neural densities, and a poorer orientation discrimination of individual path elements, its capacity to link these elements into a contour equals that of the other two systems.