Abstract
Numerous studies have shown that human observers are exquisitely sensitive to the visual analysis of human movement. Indeed, the visual analysis of human motion can substantially differ from the visual analysis of moving, inanimate objects such as scissors, cars, clocks, and erasers (Shiffrar, 2001). This difference might be partially due to differences in motor system activity since selective M1 activation is associated with the passive observation of normal human motion but not with observation of inanimate object motion (Stevens et al., 2000). But does human motion perception differ from all other motion processes? The goal of a series of studies was to determine whether the visual analysis of human movement differs from the visual analysis of non-human animal movement. To that end, we selected two “gold standard” characteristics of the visual analysis of human motion, orientation specificity and global spatial processing, and examined whether these characteristics could be found in the visual analyses of animal motion. Following a between subjects design, naive subjects viewed masked point light displays and reported whether they detected one of four possible walking targets: an inverted or upright human or horse. Across experiments, clear evidence for spatially global processing was found in both the horse and human conditions. Surprisingly, orientation specificity strongly depended upon what subjects saw for five seconds before beginning the experimental trials. When an inverted target was shown during instruction, performance in this presence-absence task was superior with inverted targets (whether horse or human) than with upright targets. The reverse pattern was found when an upright target was shown during instruction. Such results constrain theories of the type of information that the motor system may contribute during the visual analysis of human motion. Simply put, the visual system may classify humans as just another animal.
Supported by NEI grant R01 EY12300