Your Brain Rewrites Touch Sensations Based on Who's Doing the Touching

<p>Self-touch and interpersonal touch feel very different—self-touch sensations are attenuated. The distinction between self- and not-self not only influences properties such as intensity, but also qualitative aspects of touch. This is highlighted by the social softness illusion, wherein another person’s skin is perceived as softer and smoother than the own skin. The mechanisms underlying these qualitative differences of self- vs social touch remain unclear. Across four experiments, we explored such qualitative aspects of touch sensation in eighty-two healthy females. We investigated both the social softness illusion and self-touch across multiple body parts. We found that the social softness illusion only occurs under a specific condition: when the palm was touching the forearm. When the forearm instead touched the palm, a self-softness illusion emerged. For self-touch, we found differences between forearm touching palm and palm touching forearm, which were not directly linked to the movements of the palm or forearm. We also found an interaction between movement and velocity for pleasantness, where velocity mattered more during external than self-generated movements. Agency too influenced the qualitative aspects, particularly interacting with the velocity. We corroborate earlier studies showing a preference towards social touch for social interactions and the suggested soothing mechanism of self-touch. The hedonic benefits of self and social touch emerge for different reasons, therefore comparing these competing systems is complex. When comparing the qualitative aspects of social and self-touch, one must consider these two complimentary functions, with potentially different underlying psychological and neurophysiological substrates.</p>