Abstract: PURPOSE: Contextual modulation is well described for many aspects of high-level vision (e.g., facial attractiveness) but is relatively unexplored for the perception of walking direction. In a recent study, we observed an effect of the temporal context on perceived walking direction - namely, a repulsive perceptual aftereffect following exposure to biological patterns of motion. Here, we aim to examine the spatial contextual modulation of walking direction by measuring the perceived direction of a target walker in the presence of two flanker walkers, one on each side.
METHODS: Experiment 1 followed a within-subjects design. Participants (N = 30) completed a spatial context task by judging the walking direction of the target walker in thirteen different conditions: a walker alone in the centre; a walker with two flanking walkers either intact or scrambled at a flanker deviation of ±15°, ±30°, or ±45°. To compare spatial and temporal contextual effects within subjects, participants also completed an adaptation task in which they were asked to report whether the walking direction of a target point-light walker was to their left or right after adaptation to one of two walking directions of ±30°. In Experiment 2 (N= 40), we measured the tuning of spatial contextual modulation across a wide range of flanker deviation magnitudes ranging from 15° to 165° in 15° intervals.
RESULTS: We found the expected repulsive effects in the adaptation task but attractive effects in the spatial context task in Experiment 1. And results in Experiment 2 showed significant attractive effects across a wide range of flanker walking directions with the peak effect at around 30°.
CONCLUSIONS: This study extends our understanding of how spatial and temporal contextual modulation operate in high-level visual processing, and how this differs from contextual modulation in low-level vision.

Key words: opposite effect, contextual modulation, biological motion, social vision