Haptic perception of linear extent

Abstract

The perception of linear extent in haptic touch appears to be anisotropic, in that haptically perceived extents can depend on the spatial orientation and location of the object and, thus, on the direction of exploratory motion. Experiments 1and 2 quantified how the haptic perception of linear extent depended on the type of motion (radial or tangential to the body) when subjects explored different stimulus objects (raised lines or solid blocks) varying in length and in relative spatial location. Relatively narrow, shallow, raised lines were judged to be longer, by magnitude estimation, than solid blocks. Consistent with earlier reports, stimuli explored with radial arm motions were judged to be longer than identical stimuli explored with tangential motions; this difference did not depend consistently on the lateral position ofthe stimulus object, the direction of movement (toward or away from the body), or the distance of the hand from the body but did depend slightly on the angular position of the shoulder. Experiment 3 showed that the radial-tangential effect could be explained by temporal differences in exploratory movements, implyingthat the apparent anisotropy is not intrinsic to the structure of haptic space.How do people perceive and judge linear extentslengths or distances that vary along a single spatial dimension-when these are apprehended through selfinitiated actions in manipulatory space? Lederman, Klatzky, Collins, and Wardell (1987) define manipulatory space as the small-scale space that is explored haptically with the arm. Although quantitative studies of the perception oflinear extent in manipulatory space go back more than a century (e.g., Jastrow, 1886), some basic issues still are not fully resolved.One ofthese concerns the isotropy ofperceptual space: How uniform is perceptual space over its several possible axes? Anisotropy seems to be the rule rather than the exception in perceptual systems-and, presumably, arises from potent perceptual mechanisms, given the failure of experience to "correct" the discrepancies. Both vision and passive touch, for instance, have long been known to exhibit systematic deviations from uniformity. E. H. Weber (1834) was apparently the first to note that passive, tactile two-point spatial sensitivity depends systematically on the axis defined by the punctate stimuli. On the arm, for instance, the threshold for detecting spatial separation is smaller when the points are displaced transversely than when they are displaced longitudinally.

Direct coupling of haptic signals between hands

“…Size could be judged from the Euclidean distance between the spatial positions when touching the two extremities of the triangle. However, larger triangles may also be perceived as larger only because, on average, the stimulus had longer duration (22)(23)(24)(25)(26). We therefore analyzed reported sizes simultaneously as a function of simulated size and stimulus duration.…”

Factors affecting the haptic filled-space illusion for dynamic touch

“…For example, observers who were instructed to trace linear extents at high speeds judged these lengths to be shorter than the same extents traced at considerably lower speeds (Hollins and Goble 1988;Von Skramlik 1933;Wapner et al 1967). In the case of free exploration, linear extents oriented radially from the body were judged to be longer than extents oriented tangentially; at the same time, it was observed that the extents that were judged longer were traced at slightly lower speeds, which led to a corresponding increase in movement time (Armstrong and Marks 1999;Wong 1977). Similarly, convex lengths were overestimated compared to concave lengths; again, these overestimations correlated with diVerences in movement time that were, in turn, due to slight speed diVerences between the various surface types (Sanders and Kappers 2008).…”

Haptic perception: A tutorial

“…For example, curvature perception depends on whether the curvature is convex or concave (van der Horst & , the direction of movement over the surface (Davidson, 1972;Hunter, 1954), the position of the stimulus on the hand (Pont, Kappers, & Koenderink, 1997, 1998, and on shape features other than the judged curvature (Vogels, Kappers, & Koenderink, 1999). Haptic perception of linear extent is affected by the path length, curvature (Sanders & Kappers, 2008), rate of exploration between endpoints (Armstrong & Marks, 1999;Lederman, Klatzky, & Barber, 1985), and other linear elements in the field (Heller & Joyner, 1993).…”