A tactile illusion: The rotating hourglass

Abstract

A new tactile (more properly termed haptic) illusion, the rotating hourglass, was investigated in the laboratory by rotating a rod end for end between the S's thumb and forefinger. This illusion, which is an apparent decrease in the diameter of the rod at the point of contact with the fingers, was easily observed by 19 of the 20 Ss. When the illusion was studied as a function of time, the magnitude of the illusion increased over time with a mean decrease in apparent diameter of 52.3% from the beginning to the end of the 38-sec trials. A theory of differential adaptation of the skin is postulated to explain the rotating hourglass illusion and a similar illusion.This illusion, which we call the rotating hourglass, is an apparent decrease in the diameter of the part of a rotating rod which is in contact with the finger. Most people can experience a weak version of this illusion by using a piece of chalk. To obtain the illusion, hold the chalk in the center with the thumb and forefinger. Then steadily rotate the piece of chalk end over end with the other hand so that each end passes through the circle formed by the thumb and forefinger. While rotating the chalk end for end at 30-50 rpm, grip it fairly firmly, keep your fingers in the same location on the piece of chalk, and concentrate on the tactile sensations produced by the piece of chalk. After a short period of time, the diameter of the chalk should appear to decrease where it is in contact with the holding fingers.The purpose of this experiment was to investigate the rotating hourglass illusion in the laboratory under more controlled conditions. A tentative theory suggested that adaptation to the sensation of pressure produced by tissue movement was a probable explanation for the illusion. The rate of tissue movement over time is a negatively accelerated function of depth of deformation (Nafe & Wagoner, 1941a). The authors felt that, if the illusion was to be explained by a theory of pressure adaptation of the skin, the study of the time-course of the illusion was important and the rate of rotation of the rod might have an effect on the extent of the illusion. EXPERIMENT I MethodApparatus. To gain better stimulus control, an apparatus was constructed to rotate a rod between S's thumb and forefinger. A *Requests for reprints should be sent to Karen N. Jones, Department of Psychology, University of Oklahoma, Norman, Oklahoma 73069. schematic drawing of this apparatus is shown in Fig. 1. A steel rod (a), 6.35 mm in diam, was mounted in a flat ring (b), 1.86 em wide with an outside diameter of 5.67 em and an inside diameter of 5.60 em. The ring was mounted in three flanged rollers, whieh were tangent to the ring at three plaees around its circumference. Two of the rollers (c) served as idlers; the third roller (d) was driven by a variable-speed motor (e), which could tum the ring containing the rod at a calibrated rpm. S's thumb and forefinger encircled, but did not touch, the ring holding the rod when the thumb and forefinger were in contact with the rod.A schema...

Practopoiesis: Or how life fosters a mind

“…Every sensory modality seems to exhibit such adaptation: vision (Hurley 2002), audition (Jerger 1957;Ylikoski & Lehtosalo 1985), touch (Jones, Gettys, & Touchstone 1974), and olfaction (Dalton 2000). But the most important reason to consider neural adaptation as the underpinning of anapoiesis is the fact that adaptation does not result from fatigue of neurons (as has been often incorrectly presumed) but that neural adaptation rather reflects a certain form of cybernetic knowledge-i.e., the neuron has made a "decision" not to fire.…”

Introducing the shape-length illusion

“…The only example of another instance in which the perceived distance between the fingers is influenced by tactile input are the rotating disk and rotating hourglass illusions [2,6]. When a coin is rotated between thumb and index finger, the coin is perceived to be elongated perpendicular to the rotation axis, while the coin in the direction of the rotation axis sometimes is reported to shrink [2].…”

“…A similar effect is known as the rotating hourglass illusion. A rod rotated between thumb and index finger is perceived to be hourglass shaped [6]. The authors that found the hourglass illusion suggested that both illusions are caused by a pressure differential on the skin of the finger pad.…”

“…The authors that found the hourglass illusion suggested that both illusions are caused by a pressure differential on the skin of the finger pad. They hypothesized that the perceived pressure pattern on the skin for a rotating rod is the same as for a stationary hourglass [6]. Hence, the illusionary percept that one is holding an hourglass-like shaped object.…”

Prediction of two haptic illusions from the differential adaptation theory

“…A differential adaptation theory was proposed previously to explain two haptic illusions (Jones, Touchstone, & Gettys, 1974). In the present paper, this theory was used to produce two new illusions.…”