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The extent to which viewing a 'virtual' limb, the mirror image of an intact limb, modifies the experience of a phantom limb, was investigated in 80 lower limb amputees before, during and after repeated attempts to simultaneously move both intact and phantom legs. Subjects were randomly assigned to one of two conditions, a control condition in which they only viewed the movements of their intact limb and a mirror condition in which they additionally viewed the movements of a 'virtual' limb. Although the mirror condition elicited a significantly greater number of phantom limb movements than the control condition, it did not attenuate phantom limb pain and sensations any more than the control condition. The potential of a 'virtual' limb as a treatment for phantom limb pain was discussed in terms of its ability to halt and/or reverse the cortical re-organisation of motor and somatosensory cortex following acquired limb loss.

Research studies of 'audioanalgesia', the ability of music to affect pain perception, have significantly increased in number during the past two decades. Listening to preferred music in particular may provide an emotionally engaging distraction capable of reducing both the sensation of pain itself and the accompanying negative affective experience. The current study uses experimentally induced cold pressor pain to compare the effects of preferred music to two types of distracting stimuli found effective within the previous studies; mental arithmetic, a cognitive distraction, and humour, which may emotionally engage us in a similar manner to music. Forty-four participants (24 females, 20 males) underwent three cold pressor trials in counterbalanced order. The Paced Auditory Serial Addition Task provided the cognitive distraction and a choice was given from three types of audiotaped stand-up comedy. Participants provided their own preferred music. A circulating and cooling water bath administered cold pressor stimulation. Tolerance time, pain intensity on visual analogue scale and the pain rating index and perceived control were measured. Preferred music listening was found to significantly increase tolerance in comparison to the cognitive task, and significantly increase perceived control in comparison to humour. Ratings of pain intensity did not significantly differ. The results suggest preferred music listening to offer effective distraction and enhancement of control as a pain intervention under controlled laboratory conditions.

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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, ...

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Laboratory simulations of weightlessness have shown that the Weber fraction for mass is higher than that for weight in the range 1000-7000 g. Experiments in the weightless conditions of orbital and parabolic flight have found the same at the 50 g level. T o obtain measures at intermediate intensities, the Weber fractions for weight and mass were measured for 15 subjects at 50, 200 and 4OOg. The stimuli were canisters suspended on strings. The subjects lifted them for the weight condition and swung them firmly sideways for the mass condition. The Weber fraction was higher for mass than for weight at all intensities, and increased at 50g for both conditions. In a second mass condition, in which the subjects shook the cylinders within a loosely clenched hand, the Weber fraction remained almost constant at all intensities and was significantly smaller than for the firm swing method at 50g. The differences in performance between conditions may be related to the continuity or intermittency of pressure information. Other explanations are discussed.

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