Influences of Head and Torso Movement Before and During Affordance Perception

ABSTRACT

Previous research has shown that body sway (both standing and seated) is related to the accuracy of affordance judgments. The authors investigated the influence of seated head and torso movement on the perception of a novel affordance for wheelchair locomotion. Healthy adults without prior wheelchair experience judged the lowest lintel under which they could roll in the wheelchair. Prior to judgments, participants were given brief (≈ 2 min) practice at self-controlled wheelchair locomotion. During practice, the participant's head either was or was not restrained within the wheelchair. During the subsequent judgment session, the participant's head was or was not restrained. The accuracy of affordance judgments was influenced by restraint during the practice session and also by restraint during the judgment session. The authors collected data on head movement during the judgment session (when participants were not restrained). These data revealed that movement during judgment sessions was influenced by whether or not participants were restrained during the practice session. Overall, the results reveal that the availability of head movements (i.e., being unrestrained) and the nature of head movements (during unrestrained judgment sessions) were causally related to the accuracy of affordance judgments.

Keywords:

• affordance
• locomotion
• perception
• wheelchair

ACKNOWLEDGMENTS

The experiments were conducted as part of the doctoral dissertation of Yawen Yu at the University of Minnesota. Portions of the data were reported at the XV International Conference on Perception and Action, Minneapolis, MN, July 2009.

Notes

1. Our analyses of quantitative accuracy are approximate, and may not be related to levels of accuracy that would be sufficient for the control of behavior. Judgment accuracy might be evaluated relative to performance in terms of the height (of the blind) at which participants would duck their head when actually passing under it (cf. Oudejans et al., 1996).