Predictive processing in the cortical network of biological motion perception

Abstract

The literature on biological motion processing argues that it occurs in occipitotemporal, parietal and frontal regions of the brain. Nevertheless, the literature is currently unable to explain how this processing is affected by expectations. Although models exist to explain how biological motion is perceived, they usually ignore top-down processes. To this end, the current fMRI study presented two point-light displays (embedded in noise) on either side of the screen to the participants (N=29). One of the displays was a biological motion (walking or kicking) whereas the other one was its scrambled version. The participants were asked to report the location of the biological motion. Importantly, before the presentation of motions, the participants were shown a cue about the action type (walking or kicking) which was congruent with the motion 75% of the time. There were also two additional conditions in which the cue was uninformative about the action (neutral condition) or there were no motion stimuli at all. As expected, the action observation network (consisting of pSTS, parietal cortex and IFG) showed a clear and strong activation during the conditions that a motion was present. However, these regions have failed to significantly discriminate between congruent and incongruent conditions. It should be acknowledged that this lack of significant result might be caused by the low number of trials. In order to better investigate the connections within action observation network, a DCM analysis was conducted. The winning DCM model has successfully shown the presence of feedback connections in the biological motion processing. More specifically, the model argues that both feedforward and feedback modulatory connections are present during congruent, incongruent and neutral conditions. In sum, the study highlights the importance of incorporating top-down signals such as expectations in the computational models of biological motion perception.