The precision of proprioceptive position sense

Abstract

The purpose of this study was to determine the precision of proprioceptive localization of the hand in humans. We derived spatial probability distributions which describe the precision of localization on the basis of three different sources of information: proprioceptive information about the left hand, proprioceptive information about the right hand, and visual information. In the experiment subjects were seated at a table and had to perform three different position-matching tasks. In each task, the position of a target and the position of an indicator were available in a different combination of two of these three sources of information. From the spatial distributions of indicated positions in these three conditions, we derived spatial probability distributions for proprioceptive localization of the two hands and for visual localization. For proprioception we found that localization in the radial direction with respect to the shoulder is more precise than localization in the azimuthal direction. The distributions for proprioceptive localization also suggest that hand positions closer to the shoulder are localized more precisely than positions further away. These patterns can be understood from the geometry of the arm. In addition, the variability in the indicated positions suggests that the shoulder and elbow angles are known to the central nervous system with a precision of 0.6-1.1 degrees. This is a considerably better precision than the values reported in studies on perception of these angles. This implies that joint angles, or quantities equivalent to them, are represented in the central nervous system more precisely than they are consciously perceived. For visual localization we found that localization in the azimuthal direction with respect to the cyclopean eye is more precise than localization in the radial direction. The precision of the perception of visual direction is of the order of 0.2-0.6 degrees.

An implicit body representation underlying human position sense

“…Although many researchers have noted that position sense requires a stored model of the body's metric properties (4,6,8), we believe that our systematic investigation of this body model is unique. Many models of position sense have simply assumed that the true metric properties of the body are known (5,7). In contrast, we show that the body model is massively distorted, at least in the case of the hand.…”

“…Proprioceptive signals from afferents in muscles, joints, and skin provide information about joint flexion or extension (1,2), contributing to a representation of body posture, the postural schema (3). To perceive the absolute position of body parts in external space, however, this postural information must be combined with information about the size and shape of the body segments connecting the joints (4)(5)(6)(7)(8) (Fig. 1A).…”

The Brentano illusion influences goal-directed movements of the left and right hand to the same extent

“…Several other studies have also shown diVerences in performance between the arms (reviewed in Goble and Brown 2008). Important for the present study is the Wnding of Van Beers et al (1998), who demonstrated that the non-visual (proprioceptive) information about the position of the hand is not only more precise for the right hand for right-handed subjects, but also for left-handed ones.…”

The role of visual similarity and memory in body model distortions

“…Research suggests that localization judgments related to our body parts are based on the combination of proprioceptive signals (e.g. joint angles) and stored representation of body size and shape (Beers, Sittig, & van der Gon, 1998;Soechting, 1982). This stored representation of the body metric properties, referred to as the body model, was measured in a localization task for the hand .…”