The spatial reach of affective touch: a new perspective on social peripersonal space

Peripersonal space (PPS) is defined as a sector of space surrounding the body, serving as a sensory-motor system for hand-object interaction. This portion of space, delimited by our skin and the reach of our limbs, is mapped through the integration of multisensory stimuli arising from the body. Although touch is crucial for the multisensory integration processes within PPS, only a few studies have explored the distinct contributions of the sensory system’s dual pathways. These are represented by large myelinated Aβ nerves enabling fast discriminative touch and C-Tactile unmyelinated fibers involved in the low-pressure, slow, caress-like tactile stimulation. To overcome these lacks, we carried out three experiments in which participants underwent audio-tactile tasks, each designed to assess PPS processing under different tactile conditions. In Experiment 1 (Classic Task), we estimated PPS through the traditional task in which participants responded to discriminative tactile stimuli at different temporal delays while ignoring looming sounds. In Experiments 2 (Discriminative Task), we adapted the Classic Task by using an auditory cue as a target stimulus, while administering the discriminative tactile stimulation. This allowed us to assess PPS boundaries by reversing the sensory modality of the target stimulus, with no difference found between Classic and Discriminative Tasks. In Experiment 3 (Affective Task), we used the same protocol as in Experiment 2 applying affective touch. Results showed that PPS boundaries in the Affective Task were significantly larger than both Classic and Discriminative Tasks, suggesting the unique role of caress-like touch in shaping body-space representation.