i oi 6 THE MUSCULAR SENSE. 



That Goldscheider is justified in giving an important role to joints in the 

 sense of passive movement, is borne out by the inferiority of accuracy of percep- 

 tion of passive movement, when the limb, e.g. the leg is stretched sufficiently 

 to just separate the joint surfaces l one from another, as compared with the 

 accuracy when the joint surfaces play normally over one another. That active 

 movements are slightly better perceived than are passive, may in part be due to 

 the greater compression at joints which accompanies the former, evoking 

 presumably more joint sensation. But the sensations derived from muscles 

 and tendons are certainly also largely contributory to perceptions of passive 

 movement. 



Just as sensation of movement seems an elementary product of vision and 

 of touch, so also in the muscular sense. An image in the periphery of the 

 visual field may remain unseen, so long as it does not move, but should it move 

 it will occasion a sensation forthwith, a perception referred to "something 

 moving." Two points of contact with the skin, if both within the liminal dis- 

 tance of sensible separation, are not distinguished as differing in locality, but if 

 one of the points move over skin, though the movement be even toward the other, 

 its alteration of locality is felt at once, and a sensation of movement results, 

 though entirely within the limit of a single " Weber-circle." The feeling 

 of movement of a finger is obtainable from a finger in which the sense of 

 posture has been (temporarily) quite obliterated by strong faradisation. A 

 movement is easily felt to have occurred, even when the direction in which the 

 part has been moved is not perceived. The importance of the speed of 

 movement for perception of movements of approximately liminal perceptibility 

 is hardly intelligible if the perception depends purely on inference from 

 sensations of locality, of comparison between two sensations, one of the locus a 

 quo and a second of the locus ad quern. In the case of the fingers the duration 

 of liminal movements, perceptible as movements, is so short ('02 second) that 

 it is almost impossible for two sensations, one of end and one of beginning, to be 

 differentiated and dealt with. These arguments, brought forward by Gold- 

 scheider, seem to me to justify the supposition that simple sense-fusions of 

 " movement " can be yielded by the muscular just as by visual and tactual sense. 

 But this does not, of course, alter the probability, amounting in some cases to 

 certainty, that in many of our usual passive movements the excursion and 

 duration of which are far greater than the almost liminal movements studied 

 by Goldscheider, our perceptions of them include perceptions of the initial 

 posture, of the ultimate posture, and of intermediate positions also, and supply 

 the basis for judgments. 



Perception of active movement. The accuracy of judgment of 

 actively performed movements, that is, of movements occasioned by active 

 contraction of the muscles, is almost always examined in the form of 

 " willed " movement, and is based only in part on the performances of the 

 muscular sense. In experiments on the sensible limen of willed move- 

 ment, as regards excursion and speed, Goldscheider found the liminal 

 value slightly finer than for passive, although the difference was 

 almost negligible. Thus the average for the end finger-joint with 

 active movement is 1 0> 02-1-09, for the passive 1'0-1'8. That active 

 movements are slightly better perceived than passive, may in part be 

 due to the compression at joints that accompanies active movements 

 more than passive, and therefore generates presumably more joint- 

 sensation. 



It is possible to execute subliminal willed movements, that is, willed 

 movements so small in excursion as to be insensible to muscular sense. 

 These can be evoked by thinking vividly of the movement. 



1 Lewinsky, Virchow's Archiv, 1879, Bd. Ixxvii. S. 145. 



