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

Abstract

The stream/bounce display represents an ambiguous motion event in which two identical visual objects move toward one another and the objects overlap completely before they pass each another. In our perception, they can be interpreted as either streaming past one another or bouncing off each other. Previous studies have shown that the streaming percept of the display is generic for humans, suggesting the inertial nature of the motion integration process. In this study, chimpanzees took part in behavioral experiments using an object-tracking task to reveal the characteristics of their stream/bounce perception. Chimpanzees did not show a tendency toward a dominant "stream" perception of the stream/bounce stimulus. However, depth cues, such as X-junctions and local motion coherence, did promote the stream percept in chimpanzees. These results suggest both similarities and differences between chimpanzees and humans with respect to motion integration and object individuation processes.

Pre-coincidence brain activity predicts the perceptual outcome of streaming/bouncing motion display

“…Consistent with this account, Grove and Sakurai found streaming percepts increased as depth disparity between two discs increased in both the visual-auditory and visual-only streaming/bouncing display, although their focus was the audiovisual bounce-inducing effect (ABE) 67 . Similarly, Matsuno and Tomonaga investigated the visual streaming/bouncing display in chimpanzees and found streaming percepts increased when more depth cues were introduced 25 . Combined with the evidences and explanations above, the P2 amplitude difference between bouncing and streaming trials in the present study may reflect whether or not the subject perceived the two moving discs before their coincidence as being at the same depth plane.…”

“…Our perceptual system may compute this probability when facing a visual streaming/bouncing motion display, so the streaming percept could be dominant and the visual streaming/bouncing motion display could potentially be ambiguous. Although this probabilistic inference account is highly reasonable and has been confirmed by several studies 13 , 19 , 20 , there is little experimental evidence to support this account in the context of a purely visual streaming/bouncing motion display 19 , 25 .…”

How dolphins see the world: A comparison with chimpanzees and humans

“…They were not food-deprived and were fed fruits, vegetables, and primate chow three times each day during the study. They had previously engaged in various kinds of computer-controlled perceptual and cognitive tasks, including those involving matching to sample192122394041424344. As a result, all chimpanzee participants were already familiar with generalised identity-matching tasks at the beginning of the present experiments; thus, we did not need to conduct any acquisition training for this group.…”

Differences between chimpanzees and humans in visual temporal integration

“…Although the fundamental mechanism of motion perception in chimpanzees has not been studied well, some studies have found species differences in terms of motion integration processing 27 28 29 . For example, humans have a great advantage when detecting a stationary dot among consistently moving rather than randomly moving dots; however, chimpanzees have not shown any differences in performance based on motion coherence 27 .…”

“…In contrast, chimpanzees do not show a bias toward a “streaming” perception. This species difference can be explained in terms of abilities related to spatio–temporal integration 28 . The findings of dynamic shape perception under the slit-viewing condition extend the evidence for relative local biases in spatial and temporal processing by chimpanzees.…”