Inertial eigenvalues, rod density, and rod diameter in length perception by dynamic touch

Abstract

Four experiments addressed the relevance of the eigenvalues I k of the inertia tensor for perceiving length by dynamic touch. Experiments 1-2 focused on the consequences of limiting variation in the minimum eigenvalue 1 3 , Both revealed that perceived length is a function of I k . Whether the contribution of 1 3 is detected, however, depends on the range of values that characterize a particular object set. Experiments 3-4 considered the relationship between an independent index of a rod's diameter, which does not affect I k , and actual manipulation of a rod's diameter, which does affect I k • Whereas the former appeared as satisfaction of implicit instructions to alter reports of perceived length, the latter entailed actual differences in perceived length in accordance with I k • Results are discussed with respect to the links among actual length, perceived length, and I k , as well as, in particular, how these links guarantee that perceived length is in the range of actual lengths.When an object is grasped firmly in the hand and vielded out of view by means of movements at the wrist, ts length can be perceived. A large number ofexperiments lave shown that perceived length is a function not of the ibject's actual length but rather of its resistance to rotaional acceleration as quantified by the inertia tensor, 1/ see Appendix). In the initial research directed at the spaĩ al abilities of dynamic touch, measurements were reitricted to the coordinate-system-dependent components if Ii}, and then only to its moments of inertia, lxx,~vY' and

Perceiving the lengths of rods wielded in differentmedia

“…To be more exact, the type of scaling observed in the present results appears to be a definite scaling rather than an absolute scaling (Bingham, 1993(Bingham, , p. 1155. That is, although the participants did not exactly reproduce the absolute lengths of the rods in both media, they were able to provide estimates that were consistently within a marginal tolerance of actual values and were not merely reproducing a relative ordering of rod lengths (see Carello, Fitzpatrick, Flascher, & Turvey, 1998). The perceptions were a function of information more definite than that which would only support relative scaling.…”

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 .…”

Mechanical invariants are implicated in dynamic touch as a function of their salience in the stimulus flow.

“…Specifically, I 1 and I 3 have been claimed to form the basis of length perception (Carello, Fitzpatrick, Flascher, & Turvey, 1998;Fitzpatrick et al, 1994;Stroop, Turvey, Fitzpatrick, & Carello, 2000;Turvey, Burton, Amazeen, Butwill, & Carello, 1998), a task that has been studied extensively in dynamic touch. However, Kingma, Beek, and van Dieën (2002) have demonstrated that the identification of I 1 and I 3 as the informational basis of length perception suffered from confounding covariation between candidate mechanical invariants.…”