Abstract

Forced changes in vergence by prisms and lenses are expected to be accompanied by perceptual changes in size and distance. For example, the application of base out (BO) prism is expected to induce convergence micropsia and a decrease in apparent distance.¹ However, it has also been argued that a visually normal observer could perceive convergence micropsia and an increase in target distance, if perceived size is used as a distance cue.² It has also been reported that 1/3 of a group of visually normal subjects could not use vergence information at all,³ giving rise to yet a third possible distance response to BO prism; no change. What kinds of vergence-mediated distance percepts do observers report in the absence of other cues? This question has been investigated both clinically and in the laboratory. Unfortunately, the clinical studies have carefully documented the distribution of responses, but have not obtained the data under controlled conditions. On the other hand, the classic investigations of vergence effects on perception have generally only reported group data and ignored the clinical implications of response variability. Thus our first goal was to measure the distribution of size and distance responses to forced vergence changes induced by both prisms and lenses.

© 1987 Optical Society of America