Similar mechanisms underlie curvature comparison by static and dynamic touch

Abstract

In four experiments, we tested whether haptic comparison of curvature ranging from -41m to +41m is qualitatively the same for static and for dynamic touch. In Experiments 1 and 3, we tested whether static and dynamic curvature discrimination are based on height differences, attitude (slope) differences, curvature differences, or a combination of these geometrical variables. It was found that both static and dynamic haptic curvature discrimination are based on attitude differences. In Experiments 2 and 4, we tested whether this mechanism leads to errors in the comparison of stimuli with different lengths for static and dynamic touch, respectively. If the judgments are based on attitude differences, subjects will make systematic errors in these comparisons. In both experiments, we found that subjects compared the curvatures of strips of the same length veridically, whereas they made systematic errors if they were required to compare the curvatures of strips of different lengths. Longer stimuli were judged to be more curved than shorter stimuli with the same curvature. Weconclude that similar mechanisms underlie static and dynamic haptic curvature comparison. Moreover, additional data comparison showed that static and dynamic curvature comparison is not only qualitatively, but also quantitatively similar.When we touch an object, we get an impression of, for instance, its texture, size, temperature, and shape. The geometrical correlate of the shape of smooth objects is curvature. So, an understanding of curvature perception contributes to the comprehension of the mechanism of shape perception. In this paper, we focus on the manner in which haptic curvature discrimination takes place in the cases of static and dynamic touch. It is evident that the results are interesting in themselves, but, in addition, we are able to compare the two cases in order to investigate whether dynamic curvature comparison follows the same principles as static curvature comparison.In earlier investigations (Pont, Kappers, & Koenderink, 1995, we tested static haptic discrimination of curved strips for different placements relative to the hand and for different lengths ofthe stimuli. The strips had a length of 8 or 20 em, a width of 2 ern, and a curvature ranging from -1.8/m to +1.8/m (the curvature is the reciprocal ofthe radius of curvature, and vice versa). Performance in the conditions in which the stimuli were touched with the palmar side ofthe hand was found to depend priWe are grateful to the Netherlands Organization for Scientific Research (NWO) for funding this project. We thank Heino Blanckaert, Jasper Berben, Ronald Burger, Norbert van Woerkom, Michiel Bijlsma, Femius Koenderink, and lnge Lichtenegger for acting as observers and Sheila McNab, whose critical comments have improved the language style of the manuscript. Special thanks go to Hans Kolijn for his technical help. Correspondence concerning this article should be sent to S. C. Pont, Utrecht University, Helmholtz Instituut, Princetonplein 5, 3584 CC Utrecht, The Netherlands ...

Intermanual Transfer of the Curvature Aftereffect in Static and Dynamic Touch

“…This result is surprising, as Pont and colleagues found similar curvature discrimination thresholds for static and dynamic touch [11]. However, finding similar thresholds does not necessarily entail that similar processes are involved in the representation of curvature by static or dynamic touch.…”

Transfer of the curvature aftereffect in dynamic touch

“…Nevertheless, the shape of weakly curved stimuli can be perceived by static touch when the contact length with the stimulus is increased by placing the whole finger or several fingers together on the stimulus surface (Pont, Kappers, & Koenderink, 1997;Pont et al, 1999). The thresholds decreased with increasing contact length, up to about 0.5 m −1 for a contact length of 15 cm.…”

“…In a number of psychophysical studies, the curvature of the stimuli was below the threshold for static touch with a single fingertip (Davidson, 1972;Gordon & Morison, 1982;Pont et al, 1999). Hence, movement was required to perceive the shape of the surface.…”

“…Neurophysiological studies have provided evidence that curvature information is processed on the basis of the response profile of the population of mechanoreceptors in the fingerpad. This response profile correlates to the contact shape and the force that is applied to the finger (Goodwin, Browning, & Wheat, 1995;Goodwin, Macefield, & Bisley, 1997;Jenmalm, Birznieks, Goodwin, & Johansson, 2003;LaMotte & Srinivasan, 1993 unsuitable to perceive the shape of weakly curved surfaces, i.e., when the curvature is below the 84% threshold of about 7 m −1 (Goodwin, John, & Marceglia, 1991;Pont, Kappers, & Koenderink, 1999).…”

Haptic perception: A tutorial

“…People can scale local curvature over a large range, from flat to 107 m 1 ; note that the curvature is inversely related to the radius of curvature (Louw, Kappers, & Koenderink, 2000;Wheat & Goodwin, 2001). Larger curves explored by touching multiple points, whether statically or dynamically, appear to be judged by the difference in local slope at different points of contact (Pont, 1997;Pont, Kappers, & Koenderink, 1999).…”