Influence of the body schema on mirror-touch synesthesia

Abstract

Individuals with mirror-touch synesthesia (MTS) report feeling touch on their own body when seeing someone else being touched. We examined how the body schema - an on-line representation of body position in space - is involved in mapping touch from a viewed body to one's own body. We showed 45 mirror-touch synesthetes videos of a hand being touched, varying the location of the viewed touch by hand (left, right), skin surface (palmar, dorsal) and finger (index, ring). Participant hand posture was either congruent or incongruent with the posture of the viewed hand. After seeing the video, participants were asked to report whether they felt touch on their own body and, if so, the intensity and location of their percepts. We found that participants reported more frequent and more veridical (i.e., felt at the same somatotopic location as the viewed touch) mirror-touch percepts on posturally congruent versus posturally incongruent trials. Furthermore, participant response patterns varied as a function of postural congruence. Some participants consistently felt sensations on the hand surface that was stimulated in the video - even if their hands were in the opposite posture. Other participants' responses were modulated based on their own hand position, such that percepts were more likely to be felt on the upright, plausible hand surface in the posturally incongruent condition. These results provide evidence that mapping viewed touch to one's own body involves an on-line representation of body position in space.

The validated touch-video database

“…For instance, stimuli depicting pain or threatening touch experiences, such as a knife tip touching a face, have been shown to elicit more frequent and intense vicarious responses compared to stimuli showing touch with non-threatening objects like a fingertip or feather (Holle et al, 2011; Ward et al, 2018; Ward and Li, 2022). Apart from emotional factors, research has also shown that physical aspects like congruent body posture and the viewer’s perspective can modulate vicarious sensory perception (Holle et al, 2011; Medina and DePasquale, 2017). Studies often incorporate a wide range of visual touch stimuli that vary in perceived arousal and threat, the body part touched, hedonic qualities, viewing perspective, and the plausibility of the visual cue (e.g., touch to an upright face versus an inverted one).…”

The relationship between mirror-touch synaesthesia and empathy: New evidence and a new screening tool

“…Although the visuo-tactile interference task of Banissy and Ward (2007) has been shown to offer a good way of identifying people with MTS, it requires bespoke equipment that is not readily accessible and requires different labs to establish their own baseline measures (tailored to their own equipment). An alternative approach that we (Holle, Banissy, Wright, Bowling, & Ward, 2011) and others (e.g., Baron-Cohen et al, 2016;Medina & De Pasquale, 2017) have used is to present participants with movies depicting touch and note the frequency and/or intensity of any felt tactile sensations. But how many tactile sensations need to be reported to meet the criteria for having MTS-one stimulus, all stimuli, or somewhere in between?…”

Characteristics of vicarious touch reports in a general population

“…While existing literature has provided valuable insights, it has often directed its focus towards a specific group known as 'mirror-touch synesthetes'. This small subset of individuals reportedly experiences vicarious sensations in a manner distinct from the broader population (Holle et al, 2011;Ioumpa et al, 2019;Li et al, 2022;Medina and DePasquale, 2017;Ward et al, 2018;Ward and Li, 2022). The aim of our exploratory study was to investigate the characteristics of reported vicarious sensations in a large sample of naïve undergraduate students.…”

“…Earlier studies employed a broad range of stimuli varying in aspects like arousal, threat, valence levels, the specific body part touched, viewing perspective, and stimulus plausibility (e.g., upright vs. inverted face). While some research has examined the influence of factors like body posture on reported sensations (Holle et al, 2011; Medina and DePasquale, 2017), there are other nuances that require further exploration for a comprehensive understanding of their effects. For example, evidence suggests that stimuli portraying painful events may be more likely to elicit vicarious responses (Ward et al, 2018; Ward and Li, 2022).…”

“…A core limitation in our current understanding of vicarious touch is that much of what is known comes from studies on individuals with mirror-touch synaesthesia (Banissy and Ward, 2007;Banissy et al, 2009;Blakemore et al, 2005;Gillmeister et al, 2017;Holle et al, 2013Holle et al, , 2011Ioumpa et al, 2019;Medina and DePasquale, 2017;Ward et al, 2018). This rare condition is characterised by frequent and intense localised tactile sensations, such as touch or pressure, rather than generalised sensations like tingling or itching (Banissy et al, 2009).…”