Temporal and spatial contextual modulation of walking direction in biological motion

The direction in which we perceive another person walking offers a crucial cue to their intentions, but how the brain encodes walking direction remains relatively unexplored. The present thesis investigates the effects of temporal and spatial context on perceived walking direction, employing biological patterns of motion – point light animations. Chapter 2 uses an adaptation technique to investigate the sensory coding of perceived walking direction, and finds that adaptation to a specific walking direction results in repulsive perceptual aftereffects. The observed tuning profiles are well explained by a population coding model, in which perceived walking direction is coded in terms of the relative activity across a bank of sensory channels with peak tuning distributed across the full 360° range of walking directions. Chapter 3 demonstrates specificity in these perceptual aftereffects in how horizontal (azimuth) walking direction is coded when moving away from the observer compared to when moving towards the observer and specificity for walking direction compared to a non-biological form of 3D motion (a rotating sphere). These results indicate the existence of neural mechanisms in the human visual system tuned to specific walking directions, provide insight into the number of sensory channels, and how their responses are combined to encode walking direction, and demonstrate the specificity of adaptation to biological motion. Spatial contextual modulation of walking direction is examined in Chapter 4 by measuring the perceived direction of a target point-light walker in the presence of two flanker walkers, one on each side. An attractive effect is found in the spatial task, and a comparison of spatial and temporal contextual effects on perceived walking direction reveals opposing effects within the same participants. Tuning of spatial contextual modulation is measured across a wide range of flanker deviation magnitudes (15° to 165° in 15° intervals). The results show significant attractive effects across a wide range of flanker walking directions with the peak effect at around 30°. This perceptual assimilation between adjacent walkers can be explained by summation of neural population responses within a spatial receptive field that encompasses both target and flanking walkers. The assimilative versus repulsive effects of spatial contextual modulation and temporal adaptation suggest dissociable neural processes operating on the same population of sensory channels, as evidenced by similarity in the peak tuning of spatial and temporal effects across the walking direction of the inducers.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2024

Author dc:creator

• Chen, Chang

• visual aftereffect
• point-light walker
• social vision
• person perception
• contextual modulation
• gain control
• biological motion
• anzsrc-for: 52 PSYCHOLOGY

Statement dc:rights

• open access
• CC BY 4.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

en

Identifier

https://doi.org/10.26190/unsworks/30161

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/102240