Visual search by chimpanzees (Pan troglodytes)

Masaki Tomonaga

Kyoto University, Japan

Visual search and related tasks are frequently used in the study of human visual information processing. These tasks have revealed many interesting phenomena directly related to the feature integration theory: pop-out, search asymmetry, conjunction search, etc. Based on these findings, this theory was modified and alternative models have also been proposed. I have been studying the visual perception and cognition in chimpanzees using these tasks. In a typical visual search task, the subject was shown the search display containing one target and several uniform distractors. The subject was required to search the display, detect the target, and touch it. In these experiments I explored the validity of the human-based model to the other animals from the standpoint of comparative perception/cognition. In the first series of experiments, I tested the search asymmetry. When the target contains a "feature" but distractors do not, humans detect the target quickly and accurately. When the distractors contain features but the target does not, conversely, humans show difficulty in detecting the target. The chimpanzees also showed an evidence for search asymmetries using simple forms such as line orientations, geometric figures, and length of lines. Recent advances in human research suggest that the search asymmetry is not limited to the simple visual processing, but is occurred in the later stage of visual processing such as object recognition. Humans show the search asymmetries in the visual search for faces, facial expressions, familiar objects, and so on. These facts, together with the other findings, are now challenging the validity of the feature integration theory. In chimpanzees also, search asymmetries were observed when using more complex forms such as orientations of faces, biological motion patterns. Research with nonhuman primates on the basis of comparative perspective will add more fruitful information for the understanding human information processing and its evolutionary origin.

Tomonaga, M. (1993). A search for search asymmetry in chimpanzees (Pan troglodytes). Perceptual and Motor Skills, 76, 1287-1295.

Tomonaga, M. (1999). Visual texture segregation by the chimpanzee (Pan troglodytes). Behavioural Brain Research, 99, 209-218.

Tomonaga, M. (in press). Investigating visual perception and cognition in chimpanzees (Pan troglodytes) through the visual search and related tasks: From basic to complex processes. In T. Matsuzawa (Ed.), Primate Origin of Human Cognition and Behavior. Tokyo : Springer.

Tomonaga, Masaki

Section of Language and Intelligence,

Primate Research Institute, Kyoto University

Inuyama, Aichi 484-8506, Japan

tomonaga@pri.kyoto-u.ac.jp