Local Biological Motion Research Articles

Asymmetry in visual search for local biological motion signals

Asymmetry in visual search for local biological motion signals

Searching for Life Motion Signals

The visual search paradigm has been widely used to study the mechanisms underlying visual attention, and search asymmetry provides a source of insight into preattentive visual features. In the current study, we tested visual search with biological-motion stimuli that were spatially scrambled or that represented feet only and found that observers were more efficient in searching for an upright target among inverted distractors than in searching for an inverted target among upright distractors. This suggests that local biological-motion signals can act as a basic preattentive feature for the human visual system. The search asymmetry disappeared when the global configuration in biological motion was kept intact, which indicates that the attentional effects arising from biological features (e.g., local motion signals) and global novelty (e.g., inverted human figure) can interact and modulate visual search. Our findings provide strong evidence that local biological motion can be processed independently of global configuration and shed new light on the mechanisms of visual search asymmetry.

Perception of animacy and direction from local biological motion signals

We present three experiments that investigated the perception of animacy and direction from local biological motion cues. Coherent and scrambled point-light displays of humans, cats, and pigeons that were upright or inverted were embedded in a random dot mask and presented to naive observers. Observers assessed the animacy of the walker on a six-point Likert scale in Experiment 1, discriminated the direction of walking in Experiment 2, and completed both the animacy rating and the direction discrimination tasks in Experiment 3. We show that like the ability to discriminate direction, the perception of animacy from scrambled displays that contain solely local cues is orientation specific and can be well-elicited within exposure times as short as 200 ms. We show further that animacy ratings attributed to our stimuli are linearly correlated with the ability to discriminate their direction of walking. We conclude that the mechanisms responsible for processing local biological motion signals not only retrieve locomotive direction but also aid in assessing the presence of animate agents in the visual environment.

Gender discrimination in biological motion displays based on dynamic cues

Studies of human locomotion have found that male and female walkers differ in terms of lateral body sway, with males tending to swing their shoulders from side to side more than their hips, and females tending to swing their hips more than their shoulders. Experiments reported here demonstrate that naive viewers can identify the gender of the figure in a biological motion display very reliably when the display contains gender-specific lateral body sway. Sensitivity to gender is high even for displays containing only a fraction of a step cycle. This dynamic cue dominates structural cues based on torso shape (`centre-of-moment9) when the cues are set in opposition. It is mediated by gender-specific differences in the velocity of shoulder and hip dots, not by positional differences in shoulder and hip dots during the step cycle.

Low-level visual processing of biological motion

Biological motion displays depict a moving human figure by means of just a few isolated points of light attached to the major joints of the body. Naive observers readily interpret the moving pattern of dots as representing a human figure, despite the complete absence of form cues. This paper reports a series of experiments which investigated the visual processes underlying the phenomenon. Results suggest that (i) the effect relies upon responses in low-level motion-detecting processes, which operate over short temporal and spatial intervals and respond to local modulations in image intensity; and (ii) the effect does not involve hierarchical visual analysis of motion components, nor does it require the presence of dots which move in rigid relation to each other. Instead, movements of the extremities are crucial. Data are inconsistent with current theoretical treatments.