Haptically perceiving the distances reachable with hand-held objects.

Abstract

Nine experiments are reported on the ability of people to perceive the distances reachable with hand-held rods that they could wield by movements about the wrist but not see. An observed linear relation between perceived and actual reaching distances with the rods held at one end was found to be unaffected by the density of the rods, the direction relative to the body in which they were wielded, and the frequency at which they were wielded. Manipulating (a) the position of an attached weight on an otherwise uniformly dense rod and (b) where a rod was grasped revealed that perceived reaching distance was governed by the principal moment(s) of inertia (I) of the hand-rod system about the axis of rotation. This dependency on moment of inertia (I) was found to hold even when the reaching distance was limited to the length of rod extending beyond an intermediate grasp. An account is given of the haptic subsystem (hand-muscles-joints-nerves) as a smart perceptual instrument in the Runeson (1977) sense, characterizable by an operator equation in which one operator functionally diagonalizes the inertia and strain tensors. Attunement to the invariants of the inertia tensor over major physical transformations may be the defining property of the haptic subsystem. This property is discussed from the Gibsonian (ecological) perspectives of information as invariants over transformations and of intentions as extraordinary constraints on natural law.

Perceiving the width and height of a hand-held object by dynamic touch.

“…The results of Solomon and Turvey's (1988) study and Solomon et al's (1989aSolomon et al's ( , 1989b) studies suggested a simple power function with an exponent less than 1 governing length perception by dynamic touch -specifically, the perceived lengths of cylindrical objects tend to increase as the cube root of 7 t : perceived length « Ii m . With respect to the present experiment, the simple regression of the logarithm of mean H P on the logarithm of I\ was highly significant, r 2 (8) = .95, p < .0001, with a slope of .33 and fiducial limits of .26-.40 (the 95% confidence intervals defining the boundaries within which a parameter is considered to be localized).…”

Transfer of Calibration Between Length and Sweet-Spot Perception by Dynamic Touch

“…The rationale was twofold. First, earlier studies have provided ample evidence that people have definite impressions of both the length (e.g., Pagano et al, 1993;Solomon & Turvey, 1988;Turvey & Carello, 1995) and the center of percussion Cooper et al, 1999) of unseen, wielded rods. A rod's center of percussion, also known as its sweet spot, 1 is the place on the rod at which it is best to hit an object; it produces the least initial shock to the hand.…”

“…This paradigm is convenient for several reasons. First, using the dynamic touch system, one is capable of perceiving several properties of the hand-held object: length (e.g., Solomon & Turvey, 1988), heaviness (e.g., Amazeen & Turvey, 1996), center of percussion (e.g., Carello, Thuot, Anderson, & Turvey, 1999;Carello, Thuot, & Turvey, 2000), shape (Burton, Turvey, & Solomon, 1990), and width and height (e.g., Turvey, Burton, Amazeen, Butwill, & Carello, 1998). Second, dynamic touch needs to be calibrated.…”

“…Earlier studies have shown that length perception of homogeneous rods is, in general, relatively but not absolutely correct. Relatedly, it has been demonstrated that the values of the calibration coefficients that would yield metrically correct length perception differ for same-sized rods made of different materials: Rods of the same length but made of materials of different densities are perceived to be of different lengths (Fitzpatrick, Carello, & Turvey, 1994;Solomon & Turvey, 1988). Thus, different calibration is needed for rods of different densities.…”

Which Mechanical Invariants Are Associated With the Perception of Length and Heaviness of a Nonvisible Handheld Rod? Testing the Inertia Tensor Hypothesis.

“…For instance, high correlations have been reported between I 1 (either alone or in combination with I 3 ) and the perceived length of an object (Carello, Fitzpatrick, Flascher, & Turvey, 1998;Fitzpatrick et al, 1994;Pagano et al, 1993;Solomon & Turvey, 1988;Solomon, Turvey, & Burton, 1989;Turvey, Burton, Amazeen, Butwill, & Carello, 1998). In addition, perceived object width has been found to correlate with the eigenvalues of the inertia tensor .…”