Affective sounds entering the peripersonal space influence the whole-body action preparation

The peripersonal space (PPS), the space surrounding us, is found to have enhanced multisensory-motor representation in the brain. In this study, we investigate how approaching sounds stopping at different distances within the peripersonal space, and carrying emotional content (positive, negative, and neutral), modulate the preparation of action as performing a Step. Premotor reaction times were measured by means of anticipatory forces and muscular activations to capture action preparation, the kinematics of stepping was considered for defining action performance, and for each stimulus, the individual perceived level of arousal and valence was evaluated. In general, we found a prompter premotor reaction for closer sounds compared to the farther ones and the fastest reactions detected for the neutral sound at each distance. We interpreted this time facilitation for neutral sound due to the large frequency spectrum of the stimuli and the absence of affective component and semantical content to decode. Interestingly, while at the close distance, none difference was found between positive and negative emotional stimuli, at the far distance faster reactions were present for negative compared to the positive sounds indicating that when arousal is less enhanced individuals are able to differentiate the emotional content of a sound. The kinematics observed after action initiation sustained the anticipatory results by showing that larger steps were performed when reacting to close compared to far sounds, being perceived as more arousing, and this happened particularly for neutral and negative sounds. Altogether, the results showed that action preparation is influenced by the vicinity and by the valence carried by looming auditory stimuli. For discriminating the stimuli valence, a certain distance, still within the PPS, is necessary; when instead stimuli are too close to the body valence discrimination is not performed.