Bistability and Biasing Effects in the Perception of Ambiguous Point-Light Walkers

Abstract

The perceptually bistable character of point-light walkers has been examined in three experiments. A point-light figure without explicit depth cues constitutes a perfectly ambiguous stimulus: from all viewpoints, multiple interpretations are possible concerning the depth orientation of the figure. In the first experiment, it is shown that non-lateral views of the walker are indeed interpreted in two orientations, either as facing towards the viewer or as facing away from the viewer, but that the interpretation in which the walker is oriented towards the viewer is reported more frequently. In the second experiment the point-light figure was walking backwards, making the global orientation of the point-light figure opposite to the direction of global motion. The interpretation in which the walker was facing the viewer was again reported more frequently. The robustness of these findings was examined in the final experiment, in which the effects of disambiguating the stimulus by introducing a local depth cue (occlusion) or a more global depth cue (applying perspective projection) were explored.

The facing bias in biological motion perception: structure, kinematics, and body parts

“…Brooks et al (2008) found a strong effect of figure gender on perceived in-depth orientation. Consistent with Vanrie et al (2004), male point-light walkers elicited a strong facing bias. However, the more strongly the figure was perceived as female, the more strongly it was perceived as facing away from the viewer.…”

“…One could assume, for instance, that in daily life, observers are more often confronted with a person facing toward them than with a person that is oriented away. There are, however, no natural image statistics available that show that this is indeed the case (Vanrie et al, 2004). Otherwise, it could be hypothesized that a person who is facing toward an observer is more socially or behaviorally relevant for the observer than a person who is oriented away.…”

“…On the basis of the stimulus properties, observers are expected to perceive the figure as facing toward them in half of the cases and as facing away from them in the other half. Vanrie, Dekeyser, and Verfaillie (2004;see Jackson &Blake, 2010, andJackson, Cummins, &Brady 2008, for related research on the perception of bistable biological motion stimuli), however, demonstrated that this is not what is empirically found when observers have to indicate the perceived in-depth orientation for a set of depth-ambiguous point-light actions. Several point-light stimuli, especially point-light walkers, elicit a strong facing bias.…”

The facing bias in biological motion perception: Effects of stimulus gender and observer sex

“…Yet observers show a bias toward seeing a walker facing the viewer (Vanrie, Dekeyser, & Verfaillie, 2004). Recently, we reported that this facing bias strongly depends on the gender of the walker (Brooks et al, 2008).…”

“…Since then, it has been reported that humans are able to extract a variety of behaviorally relevant characteristics, including the type of action (Dittrich, 1993;, the identity of the actor Loula, Prasad, Harber, & Shiffrar, 2005), and the actor's gender Pollick, Kay, Heim, & Stringer, 2005;Troje, 2002), emotional state (Dittrich, Troscianko, Lea, & Morgan, 1996;Montepare, Goldstein, & Clausen, 1987), and age (Montepare & Zebrowitz-McArthur, 1988). Only more recently, however, has the question of how observers interpret the in-depth orientation of point-light figures systematically been addressed (Jackson, Cummins, & Brady, 2008;Vanrie, Dekeyser, & Verfaillie, 2004;Vanrie & Verfaillie, 2006, 2008.…”