Abstract
Using scrambled point-light walkers as attentional cues, we demonstrate that upright local biological motion signals, compared to inverted ones, can automatically attract observers' spatial attention, without observers' explicit knowledge about the uprightness of the local motion signals. The location of each moving dot in the point-light walkers was spatially scrambled such that the global form and global motion information was entirely disrupted. Two sets of these scrambled moving dots, one from upright and the other from inverted walkers, were presented for 500 ms to the left and right sides of fixation respectively, serving as attentional cues in a Posner cueing paradigm. Following the cues, a small Gabor patch was presented for 100 ms either to the upright or inverted biological motion side to assess the attentional effect. Although none of the naive observers could discriminate which motion sequence was upright and which was inverted, their performance was significantly better when the test probe (Gabor patch) was presented to the upright scrambled biological motion side compared with when the same probe was presented to the inverted scrambled biological motion side. No consistent attentional effect was evident when the upright and inverted intact biological motion stimuli were presented as attentional cues. EEG measures further showed that the visual dorsal pathway responded to local properties of biological motion as early as 160 ms following the stimulus onset, prior to the processing of global biological motion information in the MT-pSTS. Together these results suggest an automatic and specialized brain mechanism of detecting local life motion signals, which presumably is important for an organism's survival.
This research was supported by grants from the James S. McDonnell foundation, the National Institutes of Health, and a Grant-in-Aid from the University of Minnesota.