Social coding of the multisensory space around us

Abstract

Multisensory integration of stimuli occurring in the area surrounding our bodies gives rise to the functional representation of peripersonal space (PPS). PPS extent is flexible according to the affective context and the target of an action, but little is known about how social context modulates it. We used an audiotactile interaction task to investigate PPS of individuals during social interaction. Participants had to detect as fast as possible a tactile stimulus while task-irrelevant looming sounds were presented, while they were paired as collaborative dyads and as competitive dyads. We also measured PPS in participants seated near an inactive individual. PPS boundaries were modulated only when participants collaborated with a partner, in the form of an extension on the right hemispace and independently of the location of the partner. This suggests that space processing is modified during collaborative tasks. During collective actions, a supra-individual representation of the space of action could be at stake in order to adapt our individual motor control to an interaction as a group with the external world. Reassessing multisensory integration in the light of its potential social sensitivity might reveal that low-level mechanisms are modified by the need to interact with others.

Keywords: audio-tactile integration; auditory space; collaborative behaviour; group membership; looming sound; peripersonal space.

Figure 1.

Experimental paradigm. (a) Participants performed the audiotactile task by responding to a tactile stimulation while a task-irrelevant sound was looming towards them from the left or right hemispace. On each trial, one tactile stimulation was delivered at one among nine possible delays from sound onset (T1 to T9), corresponding to nine possible distances of the sound source from participants' body. (b) Participants performed the task alone or in a dyad, seated side by side.

Figure 2.

Collaborative context increases PPS extent in the right hemispace. This figure reports the mean tactile reaction times (±s.e.m.) as a function of the delay of tactile stimulation delivery from sound onset for the left hemispace (left graph) and for the right hemispace (right graphs). On the left hemispace, there was no effect of the social condition on RTs, thus participants' data in the condition isolated and in dyad are pooled. In the right hemispace, the social condition impacted PPS extent, thus RTs are presented separately for isolated participants (top graph) and participants acting in dyad (bottom graph). The significant decreases of RTs are indicated by means of asterisks. The significant decrease of RTs corresponding to the critical delay at which sound starts to boost tactile processing is indicated by means of red asterisks. The red arrows illustrate the extent of PPS boundaries from participants' body. In the right hemispace, PPS is larger when participants are acting in dyad than when they are doing the task alone.

Figure 3.

Competitive context globally speeds up RTs but does not influence PPS extent. (a) This figure reports the mean tactile reaction times (±s.e.m.) as a function of the delay of tactile stimulation delivery from sound onset for the left hemispace (left graph) and for the right hemispace (right graph). There was no effect of the social condition on RTs, thus participants' data in the condition isolated and in dyad are pooled. The significant decreases of RTs are indicated by means of asterisks. The significant decrease of RTs corresponding to the critical delay at which sound starts to boost tactile processing is indicated by means of red asterisks. The red arrows illustrate the extent of PPS boundaries from participants' body. PPS extent is not modified in competitive context. (b) This figure reports the mean tactile reaction times (±s.e.m.) for the different social conditions—in isolation and in dyad—in left hemispace (left graph) and for the right hemispace (right graph). In the left and the right hemispace, RTs are significantly faster when participants performed the task in competition with another individual than alone.

Figure 4.

Lack of influence of another individual's presence on PPS extent. This figure reports the mean tactile reaction times (±s.e.m.) as a function of the delay of tactile stimulation delivery from sound onset for the left hemispace (left graph) and for the right hemispace (right graph). There was no effect of the social condition on RTs, thus participants' data in the condition isolated and in dyad are pooled. The significant decreases of RTs are indicated by means of asterisks. The significant decrease of RTs corresponding to the critical delay at which sound starts to boost tactile processing is indicated by means of red asterisks. The red arrows illustrate the extent of PPS boundaries from participants' body. PPS extent is not modified by the presence of another individual.