An Illusion of Movement Complementary to the Horizontal-Vertical Illusion

Abstract

Blindfolded subjects moved a stylus held in the hand over a standard distance of 4.5 ins. in a given direction. They then attempted to move the same distance in a direction at right angles to the first. Eight combinations of movements were investigated. The results reveal an illusion such that the extent of movements to left or right across the body is underestimated, while the extent of movements towards or away from the body in the mid-line is overestimated. The illusion applies to speed as well as extent of movement. Movement up or down in a vertical plane is equivalent to movement towards or away from the body in a horizontal plane. The interaction of this illusion with the well-known horizontal-vertical illusion of visual perception explains a failure to find any net illusory effect where lines visually displayed in different orientations were matched for length by unseen movements in similar orientations. Whether the visual and movement illusions simply co-exist or whether they are functionally related is not yet clear.

Dynamic properties of radial and tangential movements as determinants of the Haptic Horizontal-Vertical Illusion with an 'L' figure.

“…The specific relationship may be governed by the points of emphasis of particular experiments. In this regard, Reid (1954) has observed from introspective reports that under conditions that give rise to the haptic L illusion, the subjects attempt to keep the speed of movement constant while estimating the duration of movement. Thus, the apparently longer radial extent is presumably preempted by a judgment of greater elapsed time.…”

“…Such an analysis was suggested by Brown (1846Brown ( /1964) and more recently by Reid (1954), who both argued but without supporting data that the slower the speed in traversing an extent, the greater the extent appears. Such a relationship in fact was demonstrated by Wapner, Weinberg, Click, and Rand (1967), who found that with passive movement of the limb, a relatively faster (slower) speed gives rise to an apparently shorter (longer) extent.…”

“…Following Reid's (1954) documentation of the haptic horizontal-vertical illusion with an L figure, recent studies have shown that the effect is functionally related to the components of radial and tangential exploratory arm movements as described earlier by Davidon and Cheng (1964). Specifically, radial arm movements toward and away from the body, whether along the sagittal or coronal planes, are judged longer than equal tangential movements along the front or side of the body.…”

Muscular Torque Can Explain Biases in Haptic Length Perception: A Model Study on the Radial-Tangential Illusion

“…The spokes of the wheel indicate the radial directions, with the tangential directions orthogonal to them. In 1954, Reid first showed a bias in the perceived extent of arm movements ( [2]). Subsequently, it was shown that the direction of arm movement expressed in trunk-centered coordinates (radial vs. tangential) was fundamental to this bias ( [3,4]): arm movements executed in the radial direction were consistently overestimated, whereas tangential movements were underestimated.…”

A brief taxonomy of tactile illusions and demonstrations that can be done in a hardware store

“…Some of these effects carry clear relationships to visual illusions, but some do not. Reid described the vertical-horizontal illusion occurring when gauging the length of identical objects at different orientation as analog to that in vision [63]. Davidon and Cheng reported that subjects consistently overestimated the lengths of objects when using a radial movement rather than a lateral one, but disputed analogy with visual effects [17].…”