Speaker: Maryam Vaziri Pashkam,
Humans are experts at reading others’ actions. They efficiently process others’ movements in real time to predict intended future movements. Here we designed a competitive reaching task to investigate real-time body reading in a naturalistic setting. Two subjects faced each other separated by a plexiglass screen. Fingertip positions were recorded with magnetic sensors. One subject (Attacker) was instructed to tap one of two targets on the screen and the other subject (Blocker) was told to reach for the same target as quickly as possible. Reaction times, measured as the difference in the initial finger movement of the Attacker and the Blocker were fast, much faster than reaction times to a moving dot projected on the screen. This suggests Blockers use preparatory actions of Attackers to predict their goal. To further confirm the role of preparatory cues we video-taped an Attacker and systematically removed the preparatory information from the videos and showed that reaction times are slower in response to the manipulated videos. To localize the position of preparatory information in the body we occluded various body parts of the Attacker. Reaction times got slower only when most of the body of the Attacker was occluded suggesting that preparatory cues are distributed over the body of the Attacker. Finally we presented the Blockers with only the preparatory information and asked them to explicitly report the Attacker’s intended target. Accuracies in this explicit report were lower compared to the accuracies in the arm movement task suggesting implicit access to preparatory cues during arm movements. Taken together, these results suggest participants efficiently and implicitly gather preparatory cues from the body of their partner to predict their intentions well before movement begins.
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