Illustration of correlations between (i) <i>f_T</i> - <i>pleasantness</i> and (ii) <i>μ</i> - <i>pleasantness</i>.

<p>Mean±std tangential force component, <i>f_T</i>, (top) and the mean±std dynamic coefficient of friction, <i>μ</i>, (bottom) variations according to the material <i>pleasantness</i> levels±standard error being explored.</p

Illustration of correlations between (i) <i>α</i> - <i>pleasantness</i> and (ii) <i>β</i> - <i>pleasantness</i>.

<p>Illustration of the mean±std values of the decay coefficient, <i>α</i>, (top) and the mean±std values of the offset, <i>β</i>, (bottom) variations according to the material <i>pleasantness</i> levels±standard error being explored.</p

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

Illustration of the Principal Component Analysis.

<p>Representation of the two first components summarizing our data set. The co-ordinates of the components along each axis represent the strength of relationship between that variable and each component.</p

Factor loadings of each variable as determined by the Principal Component Analysis.

<p><i>pleasantness</i>: materials' pleasantness levels; <i>f_N</i>: normal force component; <i>β</i>: the magnitude of friction-induced vibrations in the spatial domain; <i>α</i>: decay coefficient of friction-induced vibrations in the spatial domain; <i>μ</i>: dynamic coefficient of friction; <i>v</i>: exploration velocity.</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

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