Spatial summation for complex bar patterns

Abstract

We have obtained contrast detection thresholds for spatial grating patterns of limited coherence length for square target fields subtending 2 × 2′ up to 4 × 4°. The results are consistent with a form of physiological summation in which the spatial numerical energy determines the detectability of the pattern. The limited coherence length permits us to uncouple the relationship between the target extent and the number of “coherent” periods in the pattern. Threshold is determined by the target extent, not by the number of coherent periods. A small effect of coherence length has been observed, coherent patterns being more detectable than less coherent ones, even for very long coherence lengths.