Sensorimotor mechanisms in weight discrimination

Abstract

The role of efferent and afferent signals in weight discrimination was investigated by using the tonic vibratory reflex contraction ofthe biceps muscle. Differential thresholds were obtained for two lifting conditions (normal and reflex) and two static conditions (with and without muscular tonus). Normal lifting gave finer discrimination than reflex lifting (Experiment 1). Normal lifting was also superior to the two static conditions (Experiment 2). Within the static conditions, the addition of muscular tonus gave finer discrimination. The reflex lifting condition gave thresholds similar to those for static holding with muscular tonus, lying between those for normal active lifting and those for static pressure. The reflex lifting and pressure-sensing thresholds were very much finer than the previous literature suggests. The relative contributions of efference and afference to weight discrimination are discussed.The sensory mechanisms underlying weight perception have been debated for a century and a half. Weber (1834/1978) put it thus:The weight of an object is perceived in two ways: first by the touch-sense in the skin, and then by the special sense of the voluntary muscles. The latter sense tells us the degree of tension of the muscle when lifting weights and other objects.Weber went on to measure weight discrimination by the two methods, and concluded that purely tactile discrimination became more than twice as precise with the addition of muscular kinaesthesis. (In fact, he found average Weber fractions of about 1/3 for touch alone, and 1/14 for touch plus kinaesthesis.)In the latter half of the 19th century, extensive debate occurred over whether "sensations of innervation" or sensations from muscles formed the basis of the kinaesthetic sense. The issue was whether centrally generated (efferent) signals could be sensed in the same way as peripherally generated (afferent) signals, and it led to a great deal of fruitless controversy based on introspection and semantic hair-splitting. With the growth of experimentation and the understanding of sensory physiology, introspection as a method of scientific enquiry went out of use (Boring, 1942). However, a related debate continues in the area of motor skills. Instead of arguing about the nature of volition, modern psychologists and physiologists debate the difference between "closed-loop" and "open-loop" This work was supported by a Carnegie award to the first author, and by a grant from the Medical Research Council to the second author. We should like to thank J. R. Lackner for suggesting the TVR experiment, K. Gijsbers for suggesting the two-point discrimination experiment, and R. R. Macdonald for statistical advice.The authors' mailing address is: Department of Psychology, University of Stirling, Stirling FK9 4LA, Scotland. models of motor control (e.g., Stelmach, 1979), or "feedback" and "feed-forward" models (e.g., Roland, 1978). The interest is now in whether efferent information is used at all, either separately or in conjunction with afferent information, ...

Haptic perception: A tutorial

“…The perceived weight of an object reflects its density and structure. To some extent, weight can be perceived when an object simply rests on a stationary hand; however, active exploration-particularly lifting and wielding the object-substantially enhances the ability to judge weight (Brodie & Ross, 1984). Amazeen and Turvey (1996) proposed that the perceived weight of an obof warmth and coolness arise from physical interactions between the skin and touched surface.…”

Measuring just noticeable differences for haptic force feedback: implications for rehabilitation

“…More recent work by Brodie and Ross (1984) has yielded similar JNDs for tasks involving the active lifting of 2 oz. weights [1]. Jones (1989), in a force matching experiment about the elbow, found a JND ranging between 5% and 9% [3].…”

“…weights by the hand and arm [8]. More recent work by Brodie and Ross (1984) has yielded similar JNDs for tasks involving the active lifting of 2 oz. weights [1].…”

“…Much prior research has focused on just noticeable differences for force in human subjects but none, to our knowledge, has tailored this knowledge to the rehabilitation domain [1,3,4,7,8,9]. In the early part of the 19th century, Weber (1834/1978) measured JNDs of roughly 10% in experiments involving active lifting of 32 oz.…”

Unimanual and bimanual weight perception of virtual objects with a new multi-finger haptic interface

“…In addition, weight perception may affect the way we carry out precisión tasks which require deployment of exact forces by the user at the moment of contact between the effectors (e.g., surgical probé) and the effected objects (e.g., human organ). Research on haptics suggests that people perceive weight using both cutaneous and proprioceptive cues such as skin pressure, tactile flow and muscular activity [10,1]. For example, when we lift objects with rougher surfaces or shape facilitating effortless grip then we perceive them as lighter than objects with smoother surfaces or shape resulting in arduous grip.…”