Abstract
Biological motion perception refers to the ability to perceive and interpret the movements of animate objects, in the absence of form cues (Johansson, 1973). To date, only one study has examined this ability in elderly observers (Norman et al., 2004). These authors reported that, particularly at longer exposure durations (400 ms), biological motion perception was well-preserved in older adults. Norman et al. assessed participants' ability to recognize specific activities that, in some instances, were partially occluded. In Experiment 1 of the present study, a walker was displayed (for 200 ms) in a frontal view on half of the trials; on the remaining trials a spatially scrambled walker was presented. Stimuli were shown either in isolation, or in a scrambled walker mask comprised of 25 to 150 dots. The task on each trial was to decide whether a coherent walker was present. In Experiment 2, a walker appeared on each trial, in a profile view, and participants indicated whether it was facing left or right. The stimulus was presented alone or in a field of masking dots, as described above. Healthy elderly and young adults performed essentially at ceiling levels on both tasks when no mask was added. The presence of masking dots, however, had a much more deleterious effect on the performance of elderly participants than on that of young adults. Indeed, elderly participants' performance fell to chance levels as more masking dots were added. While the two groups differed in terms of education, and scores on both the Token Test and Digit Symbol, these differences could not account for the impairment seen in elderly participants on the biological motion perception tasks. We conclude that healthy elderly show a marked impairment in their ability to perceive biological motion in the presence of visual noise, at short exposure durations.
This research was supported by an NSERC Grant to LJ.