Francis J. Clark
Dept. of Physiol., Univ. of Nebraska, College of Medicine, Omaha, NE 68198-4575
A signal detection model of static-position and movement mechanisms involved in detecting angular displacements of joints will be presented along with experimental data. The model predicts that separate neural mechanisms exist for position and movement and the data indicate that the static-position mechanism is absent at the interphalangeal joints of the fingers. The issue of what consequences result from a lack of a static-position sense will then be explored with tests of position matching accuracy comparing joints with and without this sense. A metric for kinesthetic acuity using information transfer analysis was used from which an estimate of channel capacity could be made. These data indicate surprisingly poor kinesthetic acuity for the fingers with channel capacities from ca. 1.4 bits or 2.5 discriminable levels over a 90-deg range for the proximal interphalangeal joint of the index finger (no static-position sense) to 1.8 bits of 3.5 levels for the metacarpophalangeal joint (static-position sense present). A possible anatomical basis for this lack of a static-position sense at interphalangeal joints will be discussed along with speculations on why the fingers, where one might expect a very high kinesthetic acuity, have such a low acuity.