412 MENTAL FUNCTION 



those days the discussions (mostly with a religious bearing) concerning 

 volition were almost wholly arguments as to the "freedom" of the will, 

 as to whether the individual was free to determine alternatives for himself 

 independently of all else. Into this discussion, still undecided from the 

 biological point of view, we have no idea of going here more than to 

 suggest that every normal personality believes unalterably, whatever 

 he may say and argue, that his will is free. The whole system of human 

 justice rests upon this intuitive certainty. Physiologically, however, it 

 is very difficult to define any basis for this sort of willing. There may 

 be a bodily movement present or apparently there may be none in any 

 particular determination of choice. When a muscular movement is 

 present, there are motor ideas and motor nerve-impulses accompanying it. 

 These perhaps would not actually contract the muscles but only change 

 their tonus. When the choice is wholly a matter of thought, the motor 

 side of the process is probably located chiefly in the mechanism of 

 speech (see pages 394 and 420). 



The normal willing-process in general, comprising a stimulus and a 

 motor reaction thereto, requires an appreciable and easily measurable 

 period of time. As any one familiar with, the processes of the complicated 

 neuro-muscular system would expect, the time differs for every combi- 

 nation of events. Thus, if electrical apparatus be arranged so that some 

 part of the skin is to be touched and the reactor is to press an electrical 

 key as soon as he can after he feels the touch (the type of all determina- 

 tions of reaction-time), the time is longer when it is the toe that is touched 

 than when it is the ear. It is shorter to pressure than to light, but longer 

 to sound than to pressure. If the reactor has to decide which of two 

 possible sorts of stimuli it is (as for example red or blue) before react- 

 ing, the time is longer yet. It is longer to weak stimuli than to strong; 

 becomes shorter by practice; is longer in dull persons than in bright 

 persons, etc. By this general means many of the relations and pro- 

 cesses of mental function have been studied and thousands of exact 

 time-measurements made with the chronoscope, measuring accurately 

 to the thousandth of a second. Some individuals are accurate and 

 quick, some accurate and slow, some inaccurate and quick, and some 

 inaccurate and slow. Some persons recognize the stimuli quickly but 

 react slowly, and others are quick of muscle but slow of sense. In 

 general terms the smaller a muscle the more quickly it reacts. Habit, 

 however, has more to do with the shortness of the reaction-time than 

 anything else : for example, one reacts sooner with the index finger than 

 with the fifth. It is not difficult by practice (habit) to make a voluntary 

 movement practically automatic by continued repetition under constant 

 conditions; the reaction-time then is also much shortened. 



On the average a person touched on the hand can move his finger in 

 about 0.110 second; if the stimulus be received through the eyes, in about 

 0.180 second; and if through the ears, in about 0.120 second. If the 

 reactor be thinking of the stimulus rather than concentrating his attention 

 on the movement to be made, the reaction to light is about 0.270 second 



