Rasch-Built Measure of Pleasant Touch through Active Fingertip Exploration

Background: Evidence suggests that somatic sensation has a modality for pleasant touch. Objective: To investigate pleasant touch at the fingertip level (i.e., glabrous skin site) through the elaboration of a linear unidimensional scale that measures (i) various materials according to the level of pleasantness they elicit through active fingertip explorations and (ii) subjects according to their pleasantness leniency levels. Subjects: We enrolled 198 healthy subjects without any neurological disease. Methods: Blindfolded subjects actively explored 48 materials with their index fingertips and reported the perceived pleasantness of each on a 4-level scale. The fingertip moisture levels on each subject were measured before the experimental session. Data were analyzed using the Rasch model. Results: We elaborated unidimensional linear scale that included 37 materials according to their pleasantness of touch. The pleasantness level of 21 materials was perceived differently, depending on the fingertip moisture levels of the subjects. Conclusion: Based on our findings, we formulated a Pleasant Touch Scale. Fingertip moisture levels appeared to be a major factor for (un)pleasant feelings during active exploration

The sensation of pleasantness during tactile exploration

In everyday life, we frequently explore surfaces with our fingertips to capture aspects of their physics, such as texture or toughness. Furthermore, such explorations are often accompanied by a perception of (un)pleasantness. It is therefore of interest to investigate the relationship that could exist between the sensation of pleasantness and the physical attributes of explored surfaces. Typically, the sensation of pleasantness in touch is indirectly assessed, generating ordinal data. Such data lack fundamental psychometric properties that are essential to carry out objective and quantitative analyses. To address this problem, probabilistic measurement models (e.g. Rasch model) can be used to establish linear, unidimensional and invariant scales from ordinal scores by locating subjects and items along a single underlying scale. In this thesis, the Rasch Model has been used to establish a basis for future investigations on pleasantness perception at fingertip level. Indeed, a unidimensional, linear and invariant Pleasant Touch Scale has been developed, which classifies 37 different everyday life materials according to their pleasantness levels. The pleasantness levels suggested that the pleasantness perception, occurring during active surface exploration, had a certain correlation with aspects of the microgeometry of the surfaces as well as with the frictional properties arising when sliding fingers on them. These indications were thoroughly investigated during active and passive tactile surface exploration experiments. Moreover, the effect of surface temperature on the perception of pleasant touch was studied. In conclusion, all studies indicated that surface topography and frictional forces resulting from surface exploration are important factors for pleasantness sensation during touch with a fingertip.(MOTR - Sciences de la motricité) -- UCL, 201

Peripheral vs. central determinants of vibrotactile adaptation

Long lasting mechanical vibrations applied to the skin induce a reversible decrease in the perception of vibration at the stimulated skin site. This phenomenon of vibrotactile adaptation has been studied extensively. Yet, there is still no clear consensus on the mechanisms leading to vibrotactile adaptation. In particular, the respective contribution of (i) changes affecting mechanical skin impedance, (ii) peripheral processes, and (iii) central processes is largely unknown. Here, we used direct electrical stimulation of nerve fibers to bypass mechanical transduction processes and, thereby, explore the possible contribution of central vs. peripheral processes to vibrotactile adaptation. Three experiments were conducted. In the first, adaptation was induced using mechanical vibration of the fingertip (51 or 251 Hz vibration delivered for 8 minutes, at 40x the detection threshold). In the second, we attempted to induce adaptation using transcutaneous electrical stimulation of the median nerve (51 or 251 Hz constant-current pulses delivered for 8 minutes, at 1.5x the detection threshold). Vibrotactile detection thresholds were measured before and after adaptation. Mechanical stimulation induced a clear increase of vibrotactile detection thresholds. In contrast, thresholds were unaffected by electrical stimulation. In the third experiment, we assessed the effect of mechanical adaptation on the detection thresholds to transcutaneous electrical nerve stimuli, measured before and after adaptation. Electrical detection thresholds were unaffected by the mechanical adaptation. Taken together, our results suggest that vibrotactile adaptation is predominantly the consequence of peripheral mechanoreceptor processes and/or changes in biomechanical properties of the skin

Physical Factors Influencing Pleasant Touch during Tactile Exploration

Background: When scanning surfaces, humans perceive some of their physical attributes. These percepts are frequently accompanied by a sensation of (un)pleasantness. We therefore hypothesized that aspects of the mechanical activity induced by scanning surfaces with fingertips could be objectively associated with a pleasantness sensation. Previously, we developed a unidimensional measure of pleasantness, the Pleasant Touch Scale, quantifying the pleasantness level of 37 different materials. Findings of this study suggested that the sensation of pleasantness was influenced by the average magnitude of the frictional forces brought about by sliding the finger on the surface, and by the surface topography. In the present study, we correlated (i) characteristics of the fluctuations of frictional forces resulting from the interaction between the finger and the surface asperities as well as (ii) the average friction with the sensation of pleasantness. Results: Eight blindfolded participants tactually explored twelve materials of the Pleasant Touch Scale through lateral sliding movements of their index fingertip. During exploration, the normal and tangential interaction force components, fN and fT, as well as the fingertip trajectory were measured. The effect of the frictional force on pleasantness sensation was investigated through the analysis of the ratio fT to fN, i.e. the net coefficient of kinetic friction, m. The influence of the surface topographies was investigated through analysis of rapid fT fluctuations in the spatial frequency domain. Results showed that high values of m were anticorrelated with pleasantness. Furthermore, surfaces associated with fluctuations of fT having higher amplitudes in the low frequency range than in the high one were judged to be less pleasant than the surfaces yielding evenly distributed amplitudes throughout the whole spatial frequency domain. Conclusion: Characteristics of the frictional force fluctuations and of the net friction taking place during scanning can reliably be correlated with the pleasantness sensation of surfaces

Physical Factors Influencing Pleasant Touch during Passive Fingertip Stimulation

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. Conclusion: Pleasantness perception, resulting from passive fingertip stimulation, seems to be influenced by the surfaces’ average roughness levels and average FT occurring during fingertip stimulation

Feasibility and effectiveness of HABIT-ILE in children aged 1 to 4 years with cerebral palsy: A pilot study.

No abstract availabl

Illustration of rapid force fluctuations in terms of spatial frequencies.

<p>Rapid force fluctuations for <i>paper</i> (panel A) and for <i>sandpaper</i> (panel B). A power function was fitted to the spectrum of each sample.</p

Characterization of studied variables.

<p><i>RM-ANOVA</i>: repeated-measure analysis of variance; <i>Correlation:</i> spearman correlation between each variable and the materials' <i>pleasantness</i> levels; <i>v</i>: exploration velocity; <i>f_N</i>: normal force component; <i>f_T</i>: tangential force component; <i>μ</i>: dynamic coefficient of friction; <i>α</i>: decay coefficient of friction-induced vibrations in the spatial domain; <i>β</i>: the offset of friction-induced vibrations in the spatial domain.</p

Correlation between the ordinal pleasantness scores of the present study and the unidimensional linear pleasantness measures determined in [25].

<p>Each point represents one sample of material.</p