Independence of contour and biological-motion cues for motion-defined animal shapes

The effects of different kinds of cues on the perception of second-order motion-defined animal shapes were assessed. In the first experiment discrimination thresholds for motion-defined animals without biological motion (non-BioM) were compared with motion-defined animals with biological motion (BioM). The results show no significant difference between the two conditions, suggesting that BioM does not interact with simple contour motion. In order to isolate the relative strength and interaction between the motion cues a second experiment was conducted where four conditions were used. The first condition consisted of animal contours with non-BioM, the second condition consisted of animal contours with BioM, the third condition was composed of dots present at the joints of the animals with non-BioM, and the fourth condition was composed of dots with BioM. In all cases the animal shapes traveled across the screen for a given number of frames. As in the first experiment, the results of the second study show no interaction between cues. Furthermore, the data show that the thresholds are similar whether BioM or contour cues are presented. The only condition which is significantly different is the condition without either contour or BioM cues. It is concluded that the form representation generated from these cues in motion-defined animal shapes consists of separate mechanisms which appear equally efficient for discrimination and which do not interact with one another.