Abstract
When sandwiching two moving parallel metallic wires between both hands, one often experiences an unexpected tactile sensation known as the "velvet hand illusion" (VHI). Researchers have revealed the optimal conditions for inducing VHI, while the subjective nature of VHI remains obscure. In this article, we conducted a psychophysical experiment to investigate the quality and magnitude of the illusory sensation felt during VHI. Participants were asked to evaluate the tactile sensation of moving wires by giving tactile adjective and intensity ratings of the illusory sensation. In the same experiment, for the sake of comparison, participants also rated the sensation for various common materials one may encounter in daily life. We found that, as the intensity of the illusory sensation increased, the tactile sensation became softer, wetter, warmer, and more favorable. We also found that, when a strong illusion was reported, the sensation was similar to those for leather and fabrics rather than metallic wire, which suggests that the illusion indeed changes the perceived material category. These findings provide a better characterization of VHI as well as a better understanding of tactile texture perception.
Highlights
We are surrounded by a number of textured surfaces and feel a variety of tactile sensations characterized by their materials: the softness of sponges, bumpiness of concrete, and smoothness of fur
We characterized the sensation felt during velvet hand illusion (VHI) with tactile adjective ratings by comparison with those for common materials in order to understand the quality and magnitude of the illusory sensation felt during VHI
These studies compared the ratings among a wiretouching VHI condition, wire-touching no-VHI condition, and realvelvet-touching condition, but it still remains obscure how much the estimated sensation reflected the effect of VHI itself and how much it was affected by the physical materials of the inducing stimuli
Summary
We are surrounded by a number of textured surfaces and feel a variety of tactile sensations characterized by their materials: the softness of sponges, bumpiness of concrete, and smoothness of fur. The illusion occurs when sandwiching two moving parallel metallic wires between both hands (Fig. 1), and it induces “a strange velvety, slippery or oily sensation” [2] or the “sensation of rubbing a very smooth and soft texture like velvet” [3] even though metallic wire is physically very different from velvet. This is an important phenomenon for studying the tactile mechanism underlying texture and material perception since it is expected to provide researchers with a unique way of manipulating perceived textures and materials. The sensation felt during VHI has been described as velvety, “smooth and glistening,” or oily [3]–[6], [8] as based on Manuscript received November 19, 2014; revised September 17, 2014
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