Abstract

Efficiency, as defined by signal-detection theory, is a measure of the performance of a real observer relative to the performance of the ideal observer. Sine-wave grating detection is most efficient for patterns containing one to three cycles, suggesting receptive fields of a fairly broad spatial extent. Studies of vernier acuity, on the other hand, suggest a narrow range of spatial interaction in a direction perpendicular to the target lines. The purpose of the present study was to measure efficiency for vernier alignment as a function of the number of cycles in sinusoidal targets and to infer the spatial extent of the underlying mechanisms. We measured efficiency by obtaining vernier thresholds for Gaussian-enveloped sinusoidal targets in the presence of one-dimensional static luminance noise. The grating's width, defined as the distance between 1/e points of the Gaussian envelope, varied from 0.1 to 4 cycles. Efficiency showed the same dependence on the number of cycles for 0.5 and .2c/deg gratings. Maximum efficiencies of 70% were obtained when the Gaussian envelope width was in the range of 0.250.5 cycles. Outside this range, efficiency declined. These results indicate that the visual computation of spatial alignment can be efficient but relies on spatially narrow (and spatial-frequency broad) mechanisms.

© 1990 Optical Society of America