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

Four experiments addressed the relevance of the eigenvalues Ik of the inertia tensor for perceiving length by dynamic touch. Experiments 1-2 focused on the consequences of limiting variation in the minimum eigenvalue I3. Both revealed that perceived length is a function of Ik. Whether the contribution of I3 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 Ik, and actual manipulation of a rod's diameter, which does affect Ik. 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 Ik. Results are discussed with respect to the links among actual length, perceived length, and Ik, as well as, in particular, how these links guarantee that perceived length is in the range of actual lengths.