Temporal sampling in the perception of biological motion

Abstract

Studies on visual perception pointed to a much larger temporal summation for biological motion than for simple translational patterns. Typically, an observer needs around 2000 ms to perceive a biological stimulus while for a simple translation 600 ms are usually more than enough. Moreover, biological motion perception seems to be dependent on velocity and on the number of cycles (cf. Neri et al 1998). Biological motion is quite complex, with translational and rotational motion components. However, most experiments on biological motion perception have been done with quite low temporal samplings (ie, frame rates), between 30 and 60 Hz. Therefore, the larger temporal summation might be just a consequence of an insufficient temporal sampling of the stimuli, as used in most experiments, rather than an indicator of a perceptual impairment per se. The present study aimed to investigate the influence of temporal sampling in the perception of biological motion. A task of direction discrimination was used. Perceptual thresholds and reaction times were analyzed as a function of the temporal sampling (30 to 116 frame rate) of point-light walkers stimuli. Further studies will correlate the psychophysical data with cortical activity, using fMRI techniques.