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T. L. Bolton and Donna L. IVitJicy 



ing with free-arm movements and so gives the impression of a 

 heavier weight by the fact that the cork gives way before the 

 reacting hand less rapidly and the impression of a lighter weight 

 by giving way more rapidly. When a heavier pressure is applied, 

 sometimes the arm seems to be moving through a heavy fluid, 

 sometimes the cork seems to stick fast and refuse to start imme- 

 diately, and again the balance is apparently impelled on its return 

 by an extraneous force that acts just as the balance is reaching 

 its resting place. These dififerent forms of imagery come up at 

 different times and sometimes one will persist- during several sit- 

 tings in successions. However, we should be inclined to think 

 that the visual imagery of the moving balance is not so important 

 or decisive for discrimination as it is with free-arm lifting.^ But 

 if one gives attention to the stimulations which occur in the arm, 

 he will find the lifting movement brings out tensions, strains, and 

 stresses, first in one locality and then in another. The stimula- 

 tions of the movement shift from one locality to another just as 

 in passive pressure ; they do not appear constantly in any one 

 area. The lifting movement is accomplished now with one muscle 

 or group of muscles and now with another muscle or group of 

 muscles. This happens in spite of all the efforts and precautions 

 one may take to carry out the lifting movement in precisely the 

 same -manner. It can not be done with any certainty or regular- 

 ity. One can come nearer doing this with the balance than with 

 free-arm movements. In the case of liftmg movements the stim- 

 ulations are distributed over a much wider area than in passive 

 pressure, and hence they are more numerous and variable. They 

 affect more tendons, joints, skin areas, and muscles. A given 

 change of stimulus will cause a wider irradiation of these stim- 



'The theory, developed by Miiller and Schuman, that differences 

 in weight are discriminated by the rapidity with which one weight 

 rises and the slowness with which another rises only shifts the point upon 

 which the explanation of discrimination must turn. Upon a priori grounds 

 there is no valid reason for thinking that perceptions of rate of movement 

 are more accurate or fundamental than perceptions of resistance to move- 

 ment. As we shall suggest, all discrimination rests upon getting one com- 

 bination of. peripheral effects from one object and another combination 

 from another object. One combination means one thing and another com- 

 bination means another. 



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