Causal capture effects in chimpanzees ( Pan troglodytes )

Going forward: perceptual bias for forward-facing motion in chimpanzees

When a row of objects surrounded by a frame suddenly shifts a certain distance so that part of the row is occluded by the frame, humans perceive ambiguous apparent motion either to the left or the right. However, when the objects have "directionality," humans perceive them as moving forward in the direction in which they are pointing, which is termed forward-facing motion bias. In the present study, five experiments were conducted to address whether, and if so how, physical properties or prior knowledge about the objects affected the perception of their apparent motion in two juvenile chimpanzees (Pan troglodytes). In experiment 1, the chimpanzees did not show a clear forward-facing bias in judging the direction of motion when directed triangles were presented, whereas the human participants did. In contrast, when pictures of the lateral view of chimpanzees with quadrupedal postures were shown, there was a clear bias for going "forward" with regards to the side with the head (experiment 2). We presented pictures of dogs looking back to explore what features caused the forward-facing motion bias (experiment 3). Chimpanzees did not show any bias for these stimuli, suggesting that the direction of the head and body interactively affected the perceptual bias. Experiment 4 tested the role of the head and found that only the lateral view of the heads of chimpanzees or humans caused the bias (experiment 4). Additional tests also showed that the chimpanzees could not solve the task based only on the direction of the stimuli without motion (experiment 5). These results indicate that the perception of motion in the chimpanzees was affected by the biological features of the stimuli, suggesting their prior knowledge of the "body" from a biological (morphological and kinetic) perspective.

Dogs' looking times and pupil dilation response reveal expectations about contact causality

Contact causality is one of the fundamental principles allowing us to make sense of our physical environment. From an early age, humans perceive spatio-temporally contiguous launching events as causal. Surprisingly little is known about causal perception in non-human animals, particularly outside the primate order. Violation-of-expectation paradigms in combination with eye-tracking and pupillometry have been used to study physical expectations in human infants. In the current study, we establish this approach for dogs (Canis familiaris). We presented dogs with realistic three-dimensional animations of launching events with contact (regular launching event) or without contact between the involved objects. In both conditions, the objects moved with the same timing and kinematic properties. The dogs tracked the object movements closely throughout the study but their pupils were larger in the no-contact condition and they looked longer at the object initiating the launch after the no-contact event compared to the contact event. We conclude that dogs have implicit expectations about contact causality.

Causal reports: Context-dependent contributions of intuitive physics and visual impressions of launching

Everyday causal reports appear to be based on a blend of perceptual and cognitive processes. Causality can sometimes be perceived automatically through low-level visual processing of stimuli, but it can also be inferred on the basis of an intuitive understanding of the physical mechanism that underlies an observable event. We investigated how visual impressions of launching and the intuitive physics of collisions contribute to the formation of explicit causal responses. In Experiment 1, participants observed collisions between realistic objects differing in apparent material and hence implied mass, whereas in Experiment 2, participants observed collisions between abstract, non-material objects. The results of Experiment 1 showed that ratings of causality were mainly driven by the intuitive physics of collisions, whereas the results of Experiment 2 provide some support to the hypothesis that ratings of causality were mainly driven by visual impressions of launching. These results suggest that stimulus factors and experimental design factors - such as the realism of the stimuli and the variation in the implied mass of the colliding objects - may determine the relative contributions of perceptual and post-perceptual cognitive processes to explicit causal responses. A revised version of the impetus transmission heuristic provides a satisfactory explanation for these results, whereas the hypothesis that causal responses and intuitive physics are based on the internalization of physical laws does not.

Auditory-induced bouncing is a perceptual (rather than a cognitive) phenomenon: Evidence from illusory crescents

A central task for vision is to identify objects as the same persisting individuals over time and motion. The need for such processing is made especially clear in ambiguous situations such as the bouncing/streaming display: two discs move toward each other, superimpose, and then continue along their trajectories. Did the discs stream past each other, or bounce off each other? When people are likely to perceive streaming, playing a brief tone at the moment of overlap can readily cause them to see bouncing instead. Recent research has attributed this effect to decisional (rather than perceptual) processes by showing that auditory tones alter response biases but not the underlying sensitivity for detecting objective bounces. Here we explore the nature of this phenomenon using 'illusory causal crescents': when people perceive bouncing (or causal 'launching'), they also perceive the second disc to begin moving before being fully overlapped with the first disc (i.e. leaving an uncovered crescent). Here we demonstrate that merely playing a sound coincident to the moment of overlap can also reliably induce the perception of such illusory crescents. Moreover, this effect is due to the coincidence of the tone, per se, since the effect disappears when the tone is embedded in a larger regular tone sequence. Because observers never have to explicitly categorize their percept (e.g. as streaming)-and because the effect involves a subtle quantitative influence on another clearly visual property (i.e. the crescent's width)-we conclude that this audiovisual influence on the perception of identity over time reflects perceptual processing rather than higher-level decisions.