Can internal models of objects be utilized for different prehension tasks?
We examined if object information obtained during one prehension task is used to produce fingertip forces for handling the same object in a different prehension task. Our observations address the task specificity of the internal models presumed to issue commands for grasping and transporting objects. Two groups participated in a 2-day experiment in which they lifted a novel object (230 g; 1.2 g/cm3). On Day One, the high force group (HFG) lifted the object by applying 10 N of grip force prior to applying vertical lift force. This disrupted the usual coordination of grip and lift forces and represented a higher grip force than necessary. The self-selected force group (SSFG) lifted the object on Day One with no instructions regarding their grip or lift forces. They first generated grip forces of 5.8 N, which decreased to 2.6 N by the 10th lift. Four hours later, they lifted the same object in the manner of the HFG. On Day Two, both groups lifted the same object "naturally and comfortably" with the opposite hand. The SSFG began Day Two using a grip force of 2.5 N, consistent with the acquisition of an accurate object representation during Day One. The HFG began Day Two using accurately scaled lift forces, but produced grip forces that virtually replicated those of the SSFG on Day One. We concur with recent suggestions that separate, independently adapted internal models produce grip and lift commands. The object representation that scaled lift force was not available to scale grip force. Furthermore, the concept of a general-purpose object representation that is available across prehension tasks was not supported.
Quaney
Barbara M
BM
170A Landon Center on Aging, Department of Molecular and Integrative Physiology, University of Kansas Medical Center, 3599 Rainbow Blvd., Kansas City, KS 66160, USA. bquaney@kumc.edu
Nudo
Randolph J
RJ
Cole
Kelly J
KJ
D000328:Adult; D000704:Analysis of Variance; D005260:Female; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D008959:Models, Neurological; D011597:Psychomotor Performance / Q000502:physiology*