Tactile After-images from Static Contact

It is well known that human skin is a viscoelastic material , and the mechanical and electrophysiological responses to transient indentation have been studied and modelled. For tac-tile display system design, it is also important to determine the perceptual eeects, if any, of skin viscoelasticity. The spatial characteristics and sinusoidal steady state response of the sense of touch have been comparatively well studied. This paper describes initial work in quantifying tactile \after-images" resulting from large loads applied over several seconds to the nger tip. We rst measured nger tip relaxation responses. We then ran psychophysical experiments on human subjects to determine if viscoelastic memory aaects tactile perception. To reduce sensitivity to ne surface detail and since most teletaction systems will include an elastic layer as an anti-aliasing lter, our tests were carried out with a layer of elastic material on the nger. We found a statistically signiicant correlation between mechanical memory and perception \after-images" from large loads presented to the subjects. We ooer a possible explanation for the results based on simpliied mechanical models of the skin. INTRODUCTION In the visual domain, video monitors are built to use the well known limitations of our visual system (e.g. interlaced scanning, minimum refresh rate of 70Hz for icker free displays). This same principal could be applied to tactile displays. The properties of the slowly adapting (SAI) mechanoreceptor suggest that a relatively low temporal bandwidth tactile display might work for most quasi-static shape display applications. The shape memory alloy (SMA) actuated display designed by Kontarinis has a