The present study examined whether emotion eliciting images affected motor output when a whole body movement was concerned: gait initiation. From a standing posture, 15 young adults were instructed to initiate gait (several steps) towards pleasant or unpleasant images corresponding to a congruent (CO) or an incongruent (IC) task. The movement was performed as soon as possible after the onset of images, using a paradigm of go/nogo. Because an emotional conflict had to be overcome in IC trials, we hypothesized that the longest reaction times and lowest amplitude of early postural adjustments were found during IC trials, as compared to CO trials. We also anticipated that conflict resolution would be improved if the previous trial was IC rather than CO, as previously reported in a typical press button task. Results demonstrated longer reaction times in IC than CO trials revealing that emotional conflict resolution interfered with cognitive resources involved in motor planning. Although the peak of forward velocity reached by the centre of body mass at the end of the first step and length of this step were similar between CO and IC trials, the amplitude of early postural modifications was reduced in IC trials. All together, these findings provided supporting evidence that a defensive response, possibly a freezing-like behaviour, was implemented during IC trials, but in a transient manner. Furthermore, conflict resolution was improved when the previous trial was IC rather than CO in terms of amplitude of early postural response, but not reaction time.
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