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Emalie G McMahon, Charles Y Zheng, Francisco Pereira, Gonzalez Ray, Ken Nakayama, Leslie G Ungerleider, Maryam Vaziri-Pashkam; Humans and Machine Learning Classifiers Can Predict the Goal of an Action Regardless of Social Motivations of the Actor. Journal of Vision 2019;19(10):219. doi: https://doi.org/10.1167/19.10.219.
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© ARVO (1962-2015); The Authors (2016-present)
How do people predict the actions of others? Does social context affect prediction? What information enables prediction? To answer these questions, two participants (an “initiator” and his/her partner the “responder”) played a reaching game while video recorded. The social context was modified by asking the partners to either play competitively or cooperatively. Human subjects watched videos that were cut at different timepoints relative to when the initiator lifted his/her finger and predicted the direction of movement. Further, a support vector machine (SVM) classifier was trained to decode the direction of movement from optical flow of the videos. We found that humans and the SVM could predict the direction of movement well before the movement began. Both performed slightly better in cooperation than competition. An analysis of the speed of movement revealed that the advantage in the cooperative condition was due to slower movements. Finally, the performance of humans and the SVM was similar and correlated suggesting a simple algorithm based on instantaneous optical flow suffices to explain human levels of performance. Next, using a searchlight classification method on the videos, we investigated which pixels were most informative of the goal. The searchlight revealed that information is widely distributed throughout the body of the initiator. Further, the performance of the classifier generalized across social condition highlighting the similarity in the similarity of the distribution of information between cooperation and competition. In conclusion, our results show that subtle bodily adjustments prior to explicit execution of an action reveal action goals. Aside from the speed of movement, social context may not directly affect the availability of information. Thus, not only do we reveal our intentions in cooperation when communicating the goal is beneficial, but our movements may betray our action goals even when there is incentive to conceal the information.
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