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Alissa Jacobs, Maggie Shiffrar; Walking perception by walking observers. Journal of Vision 2004;4(8):218. doi: 10.1167/4.8.218.
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© ARVO (1962-2015); The Authors (2016-present)
Biological motion research traditionally uses stationary observers. However, in the real world, moving observers analyze the actions of others so that they can compare those actions to their own. Using a 2AFC gait speed discrimination task, Experiment 1 examined whether stationary and moving observers perceive human motion differently. Walking and stationary subjects compared the relative gait speeds of two simultaneously presented point-light walkers whose speeds ranged from 2.0 to 6.5 km/hr and always differed by 0.5 km/hr. Walking decreased gait speed sensitivity. Experiment 2 examined whether observers compare their own actions with the actions of others in the same way that they compare the actions of two other people. Subjects either compared their own gait speed with the gait speed of a point-light walker (egocentric) or the gait speeds of two point-light walkers (exocentric). Subjects in both groups walked at identical speeds and performed identical gait speed comparisons. Egocentric, but not exocentric, gait speed perception depended upon observer walking speed. Experiment 3 examined the basis for this difference. Egocentric and exocentric gait speed perception differ in their behavioral relevance and the modalities compared (visual-visual vs. visual-motor). To identify the critical factor, subjects performed the same egocentric gait speed discriminations under behaviorally irrelevant conditions. Subjects and point-light walkers either faced and walked in opposite directions or the same direction. Performance varied as a function of walking direction, suggesting that behaviorally irrelevant experience drives gait speed sensitivity. Thus, the visual analysis of human movement involves different processes depending upon observer movement.
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