Limits of Spatial Vision in Sumatran Orangutans (Pongo abelii)

Abstract

Although research with animals is often done under the assumption that visual abilities are similar across species, the visual ability of most animals, including orangutans, has not been experimentally evaluated. In this study we assessed the contrast sensitivity function (CSF) of two female zoo-housed Sumatran orangutans (Pongo abelii) aged 20 and 26 years old. Orangutans were rewarded for selecting vertical or horizontal square wave gratings at the correct orientation. Results showed a CSF similar in shape and position to that of human adults, although with lower contrast sensitivity. These lower values may be due to testing constraints or may be due to species differences. These data have implications for research on orangutan cognition, hominid evolution, and have practical implications for captive and wild management of this endangered species.