Perception of Object Unity in a Chimpanzee (Pan troglodytes)

Abstract

Identifying objects is one of the most important agendas for animals in their daily lives. Quick and correct identification of foods or predators decreases risks to their lives. However, in the natural environment, objects are not always fully visible: They are often occluded by other objects and only partly visible. Therefore the ability to complete invisible parts of objects is an essential aspect of perceptual or cognitive processes. Nevertheless, this kind of perceptual completion has not been investigated intensively in nonhuman animals. It is necessary to investigate such an ability in order to clarify its phylogenetic origin and its ecological significance. In the present study, we examined a kind of perceptual completion, called "perception of object unity."When two objects move in synchrony with the gap between them occluded, they appear to be one object rather than two. This phenomenon has been investigated not only in human adults but also human infants Kellman & Spelke, 1983;Kellman, Spelke, & Short, 1986;Slater, Morison, Somers, Mattock, Brown, & Taylor, 1990). For example, Kellman and Spelke (1983) demonstrated this phenomenon by using a habituation/dishabituation procedure in 4-month-old infants and called it "perception of object unity." This perception is not limited to real objects, as used in their Japanese Psychological Research 1997, Volume 39, No. 3, 191-199 Abstract: Perception of object unity was studied in an 18-year-old female chimpanzee (Pan troglodytes) using a two-choice delayed matching-to-sample task. The subject was trained with two rod-shaped figures which were exactly identical except that one of them had a small gap at its center. After mastering this baseline task, she was shown the figure with its center occluded by a colored rectangle. We examined the perception of the subject's matching response on either the complete or the broken rod to investigate how she perceived these partly invisible figures. In four separate experiments, the alignment and the movement of the portions above and below the occluding rectangle were manipulated. She matched the partly occluded stimuli to the complete rod as long as the alignment was sufficient. The results suggest that like human adults, the chimpanzee can perceive unity of physically separated figures.

Stream/bounce perception and the effect of depth cues in chimpanzees (Pan troglodytes)

“…Watanabe & Cavanagh, 1993). Several studies in nonhuman primates have also investigated the role of junctions (T, L, or X) in the perception of object overlap, revealing that monkeys and apes perceive the occlusion or transparency of two-dimensionally displayed objects using the clues of the junctions (e.g., Fujita & Giersch, 2005;Nagasaka, Nakata, & Osada, 2009;Sato, Kanazawa, & Fujita, 1997;Sugita, 1999). Our results, which demonstrate that the addition of X-junctions promoted streaming percepts, are consistent with the results of these studies.…”

Perceptual completion in rhesus monkeys (Macaca mulatta) and pigeons (Columba livia)

“…In adults and older infants, such perception of object unity occurs in the absence of common motion, when two static rods are merely aligned to make good continuity. Sato, Kanazawa, and Fujita (1997) recently demonstrated that an adult chimpanzee showed similar perception. They trained the subject on a matching-to-sample of one rod and two rods.…”

Visual Discrimination Learning in the Jumping Spider Phidippus regius

“…Through amodal completion, an animal can perceive a figure as a whole even if another object conceals a portion of it (Michotte, Thines, & Crabbe, 1964). Mammals (Kanizsa, Renzi, Conte, Compostela, & Guerani, 1993;Sato, Kanazawa, & Fujita, 1997), birds (Regolin & Vallortigara, 1995), fish (Sovrano & Bisazza, 2008) and even invertebrates (van Hateren et al, 1990;Zylinski, Darmaillacq, & Shashar, 2012) use this mechanism just as humans do (Kanizsa, 1979).…”