What causes the facing-the-viewer bias in biological motion?

Abstract

Orthographically projected biological motion point-light displays are generally ambiguous with respect to their orientation in depth, yet observers consistently prefer the facing-the-viewer interpretation. There has been discussion as to whether this bias can be attributed to the social relevance of biological motion stimuli or relates to local, low-level stimulus properties. In the present study we address this question. In Experiment 1, we compared the facing-the-viewer bias produced by a series of four stick figures and three human silhouettes that differed in posture, gender, and the presence versus absence of walking motion. Using a paradigm in which we asked observers to indicate the spinning direction of these figures, we found no bias when participants observed silhouettes, whereas a pronounced degree of bias was elicited by most stick figures. We hypothesized that the ambiguous surface normals on the lines and dots that comprise stick figures are prone to a visual bias that assumes surfaces to be convex. The local surface orientations of the occluding contours of silhouettes are unambiguous, and as such the convexity bias does not apply. In Experiment 2, we tested the role of local features in ambiguous surface perception by adding dots to the elbows and knees of silhouettes. We found biases consistent with the facing directions implied by a convex body surface. The results unify a number of findings regarding the facing-the-viewer bias. We conclude that the facing-the-viewer bias is established at the level of surface reconstruction from local image features rather than on a semantic level.

The relationship between social anxiety and the perception of depth-ambiguous biological motion stimuli is mediated by inhibitory ability

“…While bottom-up factors surely contribute (e.g., Schouten et al, 2011;Weech et al, 2014) our findings support that top-down influences like the sociobiological relevance of biological motion stimuli affect the facing-the-viewer bias. We found support that social interaction anxiety was positively associated with FTV scores, inhibitory performance was negatively associated with FTV scores, and inhibitory Fig.…”

“…In fact, these findings shed doubt on the significance of previous findings that the gender of point-light figures affects the facing-the-viewer bias. Other factors, such as the concavity and convexity of the angles of the limbs (Weech et al, 2014) and familiarity with point-light stimuli (Troje & Davis, 2011) also surely play a role in this bias. Given the support found for both these bottom-up and top-down processes, it appears likely that the facing-the-viewer bias results from a complex interplay between several mechanisms.…”

“…For instance, observers tend to perceive point-light displays depicting male walkers as facing towards them more often than female stimuli (Brooks et al, 2008; and men are typically viewed as more threatening than women (see Cicone & Ruble, 1978). However, later studies (e.g., Schouten et al, 2011;Weech, McAdam, Kenny, & Troje, 2014) suggest that this gender effect might occur for reasons other than gender, and so further research on the relationship between the figure gender and the facing-the-viewer bias is needed.…”

Tactile input and empathy modulate the perception of ambiguous biological motion

“…These results suggest that multisensory interaction can be modulated by an individual's cognitive traits, and conform to an unwritten social norm. This effect might arise in people with high anxiety, as mistaking an approaching person for someone who is receding might have more severe consequences than the opposite mistake (Van de Cruys et al, 2013 ; Weech et al, 2014 ). People with higher empathic concern might be more sensitive to the direction of conflicting sensory cues (as in the incongruent condition), so as to avoid a potential mistake, like those in the high-anxiety group just mentioned.…”

“…Regarding the self-serving bias, a recent study revealed that in perceiving the receding/approaching directional information for PLWs, observers with high social anxiety are less likely to report the PLW as approaching, compared to observers with low social anxiety. This bias might reflect an assumption that mistaking approach for withdrawal is worse than the reverse (Van de Cruys et al, 2013 ; Weech et al, 2014 ).…”