Abstract
Human observers exhibit a remarkable degree of visual sensitivity to the movements of other people. From the motions of a few point-lights, observers can readily identify human actions and even psychological attributes, such as gender, mood, and effort. What accounts for this exquisite level of visual sensitivity to human movement? One possibility is suggested by the fact that human movement represents the only motion category which humans both produce and perceive. To the extent that the visual and motor systems interact, this raises the question of whether observers' own bodily actions can influence their visual analysis of the human movement. To that end, we examined how well observers can compare their own movements to the movements of other people. To do this, point-light walker displays were presented next to subjects walking on a treadmill. The point-light walker always produced a physically possible gait. The gait speeds of the point-light walker and the walking subjects systematically varied between 2.0 and 6.5 km/hr across trials. In a 2AFC procedure, on each trial, subjects reported whether their speed was faster or slower than the point-light walker's speed. Across conditions, subjects wore a vest with or without weights while performing this self-relative speed discrimination task. To the extent that the visual and motor systems interact during the visual analysis of human movement, visual sensitivity to gait speed should vary as a function of observers' own motor activity. Consistent with this prediction, the results revealed accuracy increments with increases in the difference between gait speeds of the subject and point-light walker. Importantly, a systematic performance shift was evident when observers wore the weighted vest. The more weighted or fatigued the subjects, the faster the point-light walkers appeared to move. Thus, motor activity influences the visual analysis of human movement.
Over the past three decades Rüdiger Wehner' research has revolved around the general question how a 0.1-mg brain of a 10-mg insect solves complex computational tasks. In trying to answer this question he focused on the extraordinary navigational skills of visually guided desert ants, Cataglyphis, and did so by interactively combining behavioural experiments with optical, neurophysiological and neuroanatomical studies, computer simulations and, most recently, robotics implementations. This interdisciplinary enterprise has led to the analysis of a number of dedicated neural systems that deal with particular aspects of the ant's overall navigational task. How these neural modules interact provides insights into the computational strategies of neural systems and the insect' “distributed intelligence”.