PERCEPTION OF MOVEMENT. 



T015 



diminishes from the attached base to the free apex of the arm. The 

 natural movements at a joint are usually slow, in proportion as the 

 lever working at that joint is long. The natural movements at 

 the shoulder and knee are slower than those at the digital joints. 

 Movements of such speed as those of the fingers in writing hardly 

 occur at hip or at shoulder. Speed and excursion mutually support 

 one another as provocative of sensation. A movement too slow to be 

 felt, if of small excursion, becomes sensible if its excursion be pro- 

 longed. With equal movements nearly liminal in amplitude, an increase 

 of speed of execution converts an imperceptible into a perceptible. 

 By multiplying together the liminal excursions and the least speeds 

 necessary to obtain them, numerical measures of the liminal performance 

 of the muscular sense are obtained, and these, as far as concerns passive 

 movements of the upper limb, run as follows : — 



Proximal interphalangeal joint 

 Metacarpo-plialangeal . 



Wrist 



Elbow .... 



Shoulder .... 



8923-13440 

 1224-1548 

 806-3654 

 280-854 

 110-420 



The performances by the shoulder are, when thus reckoned, more 

 than forty times as delicate as those by the fingers. 



Goldscheider, mainly on account of the disturbance and defect of the sense 

 of passive movement occasioned by faradisation of the joints, concluded that 

 the deep sensitiveness of joints is a chief sensory element in the production 

 of perception of passive movement. Touch and vision are not essential to the 

 perception of the movements. Goldscheider denied importance to the afferent 

 nerves of muscle, because the liminal angle for a joint remains the same for 

 various initial positions ; but this is not a very cogent argument. 



The liminal speeds for given joints starting from various initial positions are 

 exemplified as follows : — 



Shoulder with arm horizontal . . . o, 35 per second 



,, with arm 45° below horizontal 



,, ,, above horizontal (not a pure 



movement at shoulder but 

 involving scapula and 

 vertebral column as well) . 

 Hip-joint, thigh at 180° with trunk, the leg 

 extended . . 

 ,, thigh at 90° with trunk 



„ thigh at 180° with trunk, and at the 



same time abducted 40° . 

 „ thigh at 90° with trunk, and at the 



same time abducted 40° . . . o, 33 

 thigh at 50° with trunk . . 0°-6 



0°-35 

 0°-30 



0°33 



11 



5) 



thigh nearly fully extended, thigl 



adducted to 40° 

 thigh at 180° with trunk — adduction 

 ,, ,, — abduction 



thigh at 90° with trunk — adduction 



— abduction 



Knee-joint flexed at 90° 

 flexed at 70° 



Ankle-joint flexed at 90° 

 flexed at 150° 



0°-45-0°-36 

 0°-3 -0°-25 



0°-5 



0°-38 



0°-42 



0°-6 



0°-6 



0°-8 



0°-5 



0°-9 



0°-9 



l°-4 





