Chameleons use accommodation cues to judge distance

Abstract

ANY animal that adjusts the focus of its eye lens has monocular distance information potentially available from its focusing mechanism. Such accommodation cues are independent of size and context, and thus could provide an objective measure of distance. Ingle has proposed that such information is used by monocular frogs¹ and toads², both of which he has shown to be capable of estimating distance with one eye³. There is no direct evidence, however, that any animal perceives distance as a function of the plane of focus of the image. The experiments described here demonstrate that chameleons do so in estimating the distance of their prey.