How we perceive others influences our sense of touch

The way we perceive other people has a big influence on how we interact with them. For example, attractive people are more likely to be perceived as talented than less attractive people, and this so-called "halo effect" is often reflected in our behaviour towards them. Similarly, we tend to favour people perceived to be like us over people who are perceived to be different ("in-group bias").

It turns out that the way we perceive others can also influence our own sense of touch. In a new study published in the open access journal PLoS One, researchers from the University of Bologna report that looking at photos of faces being touched strongly enhances the perception of touch on the observer's face when the photos are of people who belong the same ethnic or political group.

Vision can have a big influence on how the brain processes tactile stimuli and how we perceive our own bodies. Simple manipulations of the visual information entering the brain can induce striking illusions, in which one can be fooled into thinking that tactile sensations  originate from an artificial rubber hand, from outside the body, or from someone else's body. Similarly, magnifying a painful hand by looking at it through binoculars intensifies the pain felt, while inverting the binoculars so that the hand looks smaller than it actually is reduces the pain.

These illusions can be induced so easily because vision contributes a great deal to the mental representation of the body. The brain constructs this "body image" by integrating different types of sensory information, including tactile sensations from the body surface and proprioceptive information relating to the body's position in space. But vision can modulate these other sensory modalities, and even override them to alter the body image. Thus, vewing a part of the body being touched leads to a greater increase in activity of the corresponding part of the primary somatosensory cortex than the touch alone, and the sense of touch is enhanced as a consequence.    

Functional neuroimaging shows that observing someone else being touched also activates the somatosensory cortex, but this does not lead a tactile sensation in the observer. (In mirror-touch synaesthetes, however, there is greater activation, and a tactile sensation is experienced.) In earlier work, Andrea Serino and his colleagues found that observing touch could enhance the detection of sub-threshold tactile stimuli (that is, stimuli not intense enough to elicit a sensation of touch). This was most pronounced when the subjects observed their own face, so they wondered if touch might also be modulated by the perceived similarity between the observer and the observed.

For their new study, Serino's group recruited seven native Italians and seven Moroccan immigrants were asked to look at photographs of faces being touched by a hand. In some cases, the  face in the photograph was that of a person from the same ethnic group as the participant; in others, it was the face of a person from a different ethnic group. As the participants observed the pictures, subthreshold tactile stimuli were delivered to their faces, by means of electrodes placed on the left and right cheeks. In a second experiment, the participants were grouped according to political affiliation - conservative and liberal - and shown photographs of well-known Italian politicians.

In both experiments, all the participants reported feeling a sensation on their cheek when looking at photographs of the faces of people from the same ethnic group or of the same political affiliation being touched. Viewing pictures of people who they perceived to be "like" themselves being touched had enhanced their ability to detect the tactile stimuli applied to their own cheeks, but viewing the photographs of people "unlike" them had not, even though the intensity of the applied stimuli was exactly the same in both conditions. This effect was specific to the observation of touch, as no sensations were reported when the particpants viewed photos of "like" faces merely being approached by a hand.

The precise mechanisms underlying this phenomenon are still unclear, but these and other findings hint strongly to a link between the areas of the brain subserving the senses of touch and vision. The enhanced sense of touch most probably involves increased activation of the primary somatosensory, in which the representation of the physical self is constructed. But higher order or "association" areas are also likely to be involved, because the effect draws upon the social representations of the self and other people, which are conceptual constructs containing semantic information such as ethnic and political group. From an evolutionary perspective, such a mechanism may have evolved to promote in-group bonding, which would have been beneficial for survival.

Related:

• The body swap illusion
  
  
• How to morph into another person 
• Rubber hand feels real for amputees 
• Distorting the body image affects perception of pain 

Serino, A., et al (2009). I Feel what You Feel if You Are Similar to Me. PLoS One 4 (3) DOI: 10.1371/journal.pone.0004930.