Peripersonal space in social context is modulated by action reward, but differently in males and females

The peripersonal space (PPS) is a multisensory representation of the near-body region of space where objects appear at hand. It also represents a buffer zone protecting the body from external threats and as such it contributes to the organization of social interactions. However, how the combination of embodied objects processing and constraints inherent to social interactions contributes to PPS representation remains an open issue. By using a cooperative task where two male (N = 22) or female (N = 18) participants, sharing the same action space, were requested to select a number of stimuli on a touch-screen table, we investigated the effect of non-uniform distribution of reward-yielding stimuli on selection strategy and perceptual judgments of reachability, used as a proxy of PPS representation. The probability to select a reward-yielding stimulus (50% of the stimuli) was 75% in the proximal space of one of the two confederates. Results showed that participants initially prioritized stimuli in their proximal space and were progressively influenced by the spatial distribution of reward-yielding stimuli, thus invading their confederate’s action space when associated with higher probability of reward. The distribution of reward-yielding stimuli led to an increase of reachability threshold, but only when biased towards the participants’ distal space. Although the invasion of others’ PPS was more pronounced in male participants, the biased distribution of reward-yielding stimuli altered the reachability threshold similarly in males and females. As a whole, the data revealed that reward expectations in relation to motor actions influence both PPS exploration and representation in social context, but differently in males and females.