Abstract

An observer’s ability to detect a threshold visual target depends on his knowledge of stimulus parameters, such as the target’s color, and its spatial and temporal locus. Withholding knowledge of the spatial locus of a visual acuity target should depress visual resolution because of the close theoretical relationship between spatial resolving power and contrast sensitivity. We have examined the effects of several spatial target parameters in a visual resolution task where spatial uncertainty was present. Twelve closed E patterns (which resembled rectangular figure eights) were continuously displayed on a video monitor in a 1° diam clockface pattern. The stimulus was a 200-ms removal of the left or right vertical bar that closed the E, and the task of subjects was to identify which. Our results suggest that left and right facing E values are equally detectable. E values on-axis (3, 12, 9, and 6 o’clock positions) were more visible than E values presented off-axis (1, 4, 5, etc. o’clock). Controlling for the factor of position, sensitivity d' for randomly presented E values, in one of twelve loci, was depressed by a factor just less than the square root of the number 12 of stimulus alternatives, which is the prediction of signal detection theory for the ideal observer.

© 1988 Optical Society of America