Abstract

Using a two-alternative forced-choice method and computer graphics, we measured contrast sensitivity to a sum of 216 gratings with the same spatial frequency, phase, and contrast but with different orientations. The orientation difference () was the same between all components of the sum. The range of (0180/N) decreased with increasing number (N) of components. Contrast of each component was C/N. Contrast sensitivity was found to decline with increasing β, and the steepness of decline increased with N. However, irrespective of N, the decrease of contrast sensitivity levelled off at the largest values of . In addition, for 23, 4, and 516 components, contrast sensitivity at the largest values of β was respectively less than, equal to, and better than contrast sensitivity to a single component. These results cannot be explained by probability summation and two-dimensional spatial frequency channels with fixed bandwidths. When the Michelson contrast sensitivities were transformed to contrast sensitivities and plotted as a function of the orientation range or components, i.e., (N-1) , it was found that, irrespective of N, contrast sensitivity was at first constant, then decreased, reaching a shallow minimum, and then increased thereafter. This suggests that the effectiveness of the detecting mechanism in collecting signal energy varies little with orientation range and is only slightly affected by N.

© 1990 Optical Society of America