Abstract
Hand movements are essential for tactile perception of objects. However, the specific functions served by active touch strategies, and their dependence on physiological parameters, are unclear and understudied. Focusing on planar shape perception, we tracked at high resolution the hands of 11 participants during shape recognition task. Two dominant hand movement strategies were identified: contour following and scanning. Contour following movements were either tangential to the contour or oscillating perpendicular to it. Scanning movements crossed between distant parts of the shapes’ contour. Both strategies exhibited non-uniform coverage of the shapes’ contours. Idiosyncratic movement patterns were specific to the sensed object. In a second experiment, we have measured the participants’ spatial and temporal tactile thresholds. Significant portions of the variations in hand speed and in oscillation patterns could be explained by the idiosyncratic thresholds. Using data-driven simulations, we show how specific strategy choices may affect receptors activation. These results suggest that motion strategies of active touch adapt to both the sensed object and to the perceiver’s physiological parameters.
Highlights
Hand movements are essential for tactile perception of objects
18,701s of hand movements were recorded at high resolution from 11 human participants while performing tactile recognition task of planar shapes (1196 trials in total)
This study describes the repertoire of hand movements strategies employed by human participants when required to recognize planar (2D) object shapes
Summary
Hand movements are essential for tactile perception of objects. the specific functions served by active touch strategies, and their dependence on physiological parameters, are unclear and understudied. Initial studies of planar (2D) objects revealed that humans adapt their movement patterns to the spatial characteristics of the scanned surfaces. Speed is adjusted to the spatial frequency[14] and direction to the spatial orientation of the surface’s texture[23,24] In these studies, adaptations of hand speed and direction resulted in affecting temporal c ues[14,24] and in maintaining specific sensory cues in a given ‘working range’, likely optimal for sensation, consistent with principles of closed-loop c ontrol[11,25–27]. Studies on active touch have been providing convincing evidence that hand movements are an integral part of tactile perception and that, their general patterns are adapted to the desired objectrelated information[8,32]. We tracked the hands of participants while they perceived planar (2D) shapes and correlated the observed scanning patterns with the characteristics of the participants’ spatial and temporal tactile sensitivities
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