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Fig. 1 | Journal of NeuroEngineering and Rehabilitation

Fig. 1

From: Small forces that differ with prior motor experience can communicate movement goals during human-human physical interaction

Fig. 1

An illustration of the stepping sequences from the perspective of the leader, and example movement and force data during the partnered stepping task (PST). a The simple stepping task consisted for three steps forward, collect feet together, three steps backward, collect feet together. The simple sequence was repeated four times during the predictable PST trials. Complex sequence 1 and 2 were created using a pseudorandom sequence generator to decrease the likelihood that the follower could anticipate the step. The unpredictable PST trials consisted of performing the two complex sequences and the simple sequence in a random order as prescribed by the experimenter to the leader before each unpredictable trial. To control step frequency the leaders in each dyad received auditory cues of a consistent beat at 126 beats per minutes (bpm) via their headphones. The leaders were instructed to step on every second beat (i.e. 63 bpm). The followers did not receive any auditory cues. b Example position and velocity data of a leader (grey, dashed line) and follower (red, solid line), as well as interaction forces between their right (black line) and left (grey line) hands during a predictable and unpredictable stepping sequence. Velocity data of the follower was used to identify movement phases (grey boxes). The axial (A/P) forces were similar between the left and right hands. This was consistent across all dyads regardless of composition (i.e. expert or novice). Therefore, only the axial interaction force from the right hand of the leader/left hand of the follower was analyzed. The medial-lateral (M/L) forces were of small magnitude during the predictable and unpredictable PST. As a result they were not analyzed in detail

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