Decision processes in visual discrimination of line orientation.

The contribution of decision factors to the meridional variations in line orientation discrimination (OD) was determined for 2-alternative forced-choice experimental designs. With K. O. Johnson's (1980) formalization of decision processes in discrimination tasks, 3 decision factors were identified: decision rule, memory variance, and criterial noise. Exp I (with 13 Ss) showed the effect of experimental design on OD to be similar at horizontal and oblique standard orientations, indicating that the meridional variations in OD were not due to a decision rule anisotropy. In Exp II (with 5 Ss) the effect of the interstimulus interval was also found to be similar at both standard orientations, suggesting that the memory variance is isotropic in the orientation domain. Exps III and IV (with a total of 7 Ss) supported the hypothesis that the meridional variations in OD are not due to a criterial noise anisotropy. Results strongly suggest that the oblique effect in OD is due to sensorial factors rather than to decision factors. Therefore, they further support the hypothesis linking the anisotropy of the preferred orientation distribution of Area 17-S cells (a single physiologically defined class of cells in the primary visual cortex) and the meridional variations in OD. (58 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)