Abstract
ObjectiveTactile 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 ResultsThe 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.ConclusionPleasantness perception, resulting from passive fingertip stimulation, seems to be influenced by the surfaces' average roughness levels and average FT occurring during fingertip stimulation.
Highlights
In everyday life, we continuously explore surfaces with our fingertips
Statistical analyses were conducted to investigate a possible link between the stimulus properties (i.e. Ra, force of stimulus application (FN), FT, and TS) and their respective pleasantness levels
Pleasantness perception, resulting from passive fingertip stimulation, seems to be influenced by the surfaces’ average roughness levels and average FT occurring during fingertip stimulation
Summary
The physical parameters of contact surfaces are perceived via the stimulation of various receptors embedded in the glabrous (i.e. non-hairy) skin [1,2,3,4,5,6,7,8] They are all innervated through myelinated fibres (Ab). Adapting type I (RAI) and type II (RAII or PC) respond to dynamic changes of mechanical stimulation [1] Each of these receptors has specific end organs and has been described as being implicated in the sensation of certain tactile inputs, such as tactile spatial acuity, the detection of skin stretch, roughness, or vibrations applied to the skin [1,2,3,4,5,6,7].
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