Here we report two experiments that investigated the tactile perception of one's own skin (intrapersonal touch) versus the skin of other individuals (interpersonal touch). In the first experiment, thirteen female participants rated, along four perceptual attributes, the skin of their own palm and volar forearm, then that of several of the other participants. Ratings were made using visual analogue scales for perceived smoothness, softness, stickiness, and pleasantness. One's own skin was rated less pleasant than the skin of others. For both intra- and interpersonal touch, the forearm skin was rated smoother, softer, less sticky and more pleasant than the palmar skin. In the second experiment, ten pairs of female participants rated each other's palm and volar forearm skin, with the skin of the touched individual being assessed before and after the application of skin emollients that alter skin feel. As in the first experiment, the untreated skin of others was rated more pleasant than the participants' own skin, and the forearm versus palm differences were replicated. However, the emollient had generally larger effects on self-assessments than the assessments of others, and the site effect showed greater positive sensory and pleasantness increases for palm versus volar forearm. The disparate results of the two experiments suggest that attention, influenced by the ecological importance of the stimulus, is more important to assessment of touched skin than ownership of the skin or the contribution to self-touch made by the additional receptors in the passively touched skin. In both experiments, the pleasantness of touched skin was associated with the skin's perceived smoothness and softness, with weak trends toward negative associations with its perceived stickiness, consistent with prior research using inanimate surfaces (e.g., textiles and sandpapers).
"Although mutual grooming in humans has received much less attention from researchers than in other primates, the assessment of mutual grooming in human dyadic relationships through a scale revealed that allogrooming is quite frequent in humans (Nelson and Geher, 2007). Indeed, caressing another person's skin is fairly pleasant for the toucher (Guest et al., 2009; Morrison et al., 2010). Actively touching something soft seems to be comforting since infancy. "
[Show abstract][Hide abstract] ABSTRACT: It is assumed that social bonds in humans have consequences for virtually all aspects of behavior. Social touch-based contact, particularly hand caressing, plays an important role in social bonding. Pre-programmed neural circuits likely support actions (or predispositions to act) toward caressing contacts. We searched for pre-set motor substrates toward caressing by exposing volunteers to bonding cues and having them gently stroke a very soft cloth, a caress-like movement. The bonding cues were pictures with interacting dyads and the control pictures presented non-interacting dyads. We focused on the readiness potential, an electroencephalographic marker of motor preparation that precedes movement execution. The amplitude of the readiness potential preceding the grasping of pleasant emotional-laden stimuli was previously shown to be reduced compared with neutral ones. Fingers flexor electromyography measured action output. The rationale here is that stroking the soft cloth when previously exposed to bonding cues, a compatible context, would result in smaller amplitudes of readiness potentials, as compared to the context with no such cues. Exposure to the bonding pictures increased subjective feelings of sociability and decreased feelings of isolation. Participants who more frequently engage in mutual caress/groom a " significant other " in daily life initiated the motor preparation earlier, reinforcing the caress-like nature of the task. As hypothesized, readiness potentials preceding the caressing of the soft cloth were significantly reduced under exposure to bonding as compared to control pictures. Furthermore, an increased fingers flexor electromyographic activity was identified under exposure to the former as compared to the latter pictures. The facilitatory effects are likely due to the recruitment of pre-set cortical motor repertoires related to caress-like movements, emphasizing the distinctiveness of neural signatures for caress-like movements.
Frontiers in Psychology 01/2015; 6(16):1-9. DOI:10.3389/fpsyg.2015.00016 · 2.80 Impact Factor
"Indeed, previous studies have shown that certain physical parameters of surfaces, such as topography, roughness, and temperature, may influence the perception of pleasantness. For instance, the subjective sensation of smoothness or roughness has been associated with a pleasant – or unpleasant – perception, respectively, during active – and passive touch . Only a few studies have investigated the link between innocuous thermal sensations and pleasantness perception. "
[Show abstract][Hide abstract] ABSTRACT: Objective
Tactile explorations with the fingertips provide information regarding the physical properties of surfaces and their relative pleasantness. Previously, we performed an investigation in the active touch domain and linked several surface properties (i.e. frictional force fluctuations and net friction) with their pleasantness levels. The aim of the present study was to investigate physical factors being important for pleasantness perception during passive fingertip stimulation. Specifically we were interested to see whether factors, such as surfaces' topographies or their frictional characteristics could influence pleasantness. Furthermore, we ascertained how the stimulus pleasantness level was impacted by (i) the normal force of stimulus application (FN) and (ii) the stimulus temperature (TS).
Methods and Results
The right index fingertips of 22 blindfolded participants were stimulated using 27 different stimuli, which varied in average roughness (Ra) and TS. A 4-axis robot moved the stimuli horizontally under participants' fingertips with three levels of FN. The robot was equipped with force sensors, which recorded the FN and friction force (FT) during stimulation. Participants rated each stimulus according to a three-level pleasantness scale, as very pleasant (scored 0), pleasant (scored 1), or unpleasant (scored 2). These ordinal pleasantness ratings were logarithmically transformed into linear and unidimensional pleasantness measures with the Rasch model. Statistical analyses were conducted to investigate a possible link between the stimulus properties (i.e. Ra, FN, FT, and TS) and their respective pleasantness levels. Only the mean Ra and FT values were negatively correlated with pleasantness. No significant correlation was detected between FN or TS and pleasantness.
Pleasantness perception, resulting from passive fingertip stimulation, seems to be influenced by the surfaces' average roughness levels and average FT occurring during fingertip stimulation.
PLoS ONE 07/2014; 9(7):e101361. DOI:10.1371/journal.pone.0101361 · 3.23 Impact Factor
"The term " spontaneous " means these kinds of movements, particularly the triggering of the movements, is not based on deliberate decision-making processes of the respecting person. Contrary to other self-touching actions in experimental settings (Ackerley et al., 2012; Guest et al., 2009; Schutz-Bosbach et al., 2009; van Stralen et al., 2011; White et al., 2010) spontaneous STG are performed without a request by any other person and without any prompt by an external stimulus. These spontaneous movements are fairly common in everyday life and may be observed as a ubiquitous behaviour in people from all social classes. "
[Show abstract][Hide abstract] ABSTRACT: Spontaneous facial self-touch gestures (sFSTG) are performed manifold every day by every human being, primarily in stressful situations. These movements are not usually designed to communicate and are frequently accomplished with little or no awareness. The aim of the present study was to investigate whether sFSTG are associated with specific changes in the electrical brain activity that might indicate an involvement of regulatory emotional processes and working memory.
14 subjects performed a delayed memory task of complex haptic stimuli. The stimuli had to be explored and then remembered for a retention interval of 5 minutes. The retention interval was interrupted by unpleasant sounds from The International Affective Digitized Sounds and short sound-free periods. During the experiment a video stream of behavior, 19-channel EEG, and EMG (of forearm muscles) were recorded. Comparisons of the behavioral data and spectral power of different EEG frequency bands (theta, alpha, beta, and gamma) were conducted.
An increase of sFSTG during the application of unpleasant sounds was observed. A significant increase of spectral theta and beta power was observed after exploration of the stimuli as well as after sFSTG in centro-parietal electrodes. The spectral theta power extremely decreased just before sFSTG during the retention interval. Contrary to this, no significant changes were detected in any of the frequencies when the spectral power before and after instructed facial self-touch movements (b-iFSTG and a-iFSTG) were compared. The changes of spectral theta power in the intervals before and after sFSTG in centro-parietal electrodes imply that sFSTG are associated with cortical regulatory processes in the domains of working memory and emotions.
Brain research 04/2014; 1557. DOI:10.1016/j.brainres.2014.02.002 · 2.84 Impact Factor
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