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SCIENCE. 



[Vol. XVI. No. 397 



one of two, but 60 ff longer to name one of 26 than one of 

 two pictures, and 163(7 longer to name one of ten than one 

 of two colors; the action of naming being more closely re- 

 lated to letters and words than to pictures and colors. 



It is the ability to deal promptly and correctly with a large 

 and varying number of impressions, disposing of each in its 

 appropriate way, that we recognize as evidence of mental 

 power, and it is this that experiment shows to be a factor 

 of gi-eat influence upon the time of an adaptive re-action. 

 It is the skill in disposing of so large a number of adaptive 

 re-actions that we admire in the post-office clerk, and in many 

 other exhibitions of manual dexterity. It is this that necessi- 

 tates the division of labor, there being a limit to the number 

 of adaptive re-actions that can be economically controlled. 

 Again : the fact that a large number of distinctions does not 

 complicate the process as much as a large number of choices, 

 finds its analogue in the observation that our power of re- 

 production falls below our powers of appreciation. This 

 plays a part in the fact that we learn to understand a lan- 

 guage long before we learn to speak it, and in many similar 

 processes. The development of mental power reveals itself 

 as an increasing facility in performing a large number of 

 complicated adaptive re-actions; and here, too, the power 

 of appreciating distinctions develops earlier than the power of 

 choosing. This result was illustrated experimentally in a 

 brief study of the re-action times of a ten-year-old child as 

 compared with those of an adult. While the pure distinc- 

 tion time rose from 58(7 to 250(7 as the impressions to be 

 distinguished increased from two to five (subjective method, 

 with colors), as compared with 44(7 and 78(7 for adults, for 

 the adaptive re-action for two impressions the time was 120(7, 

 for five impressions 603(7, as compared with 79(7 and 210(7 

 for adults. 



We may conveniently introduce the general topic of the 

 effect of the nature of the distinction and the choice upon 

 the time of its performance with the consideration of a few 

 points affecting the distinction alone. (2) The similarity of 

 the impressions. The endowment of the various sense-or- 

 gans varies considerably (e.g., the sense of musical pitch is 

 finer than that of sound intensity) ; but, in the absence of a 

 standard of comparison of sense-differences in disparate types 

 of sensation, we can only illustrate the point in question by 

 varying the difficulty of distinction within the same sense. 

 Thus Kries and Auerbach find that it takes much longer to 

 tell whether a sound is to the right or to the left, according 

 as the two points at which the sound is produced are closer 

 together when they form an angle of 35°-120'' with the cen- 

 tre of the face. The additional time (by the incomplete 

 method) was 17(7; when varied between 35° and 26°, the 

 time was 78(7; when within 26° and 11°, it was 137(7. The 

 ease of distinction is largely a function of practice. We 

 readily seize the slight optical differences furnished by the 

 .different letters of a known language, but constantly con- 

 fuse much greater sense-differences with which we are less 

 familiar. (3) The specific nature of the impression. Very 

 many of the results cited in the table may be said to illus- 

 trate the effect of a change in the nature of the distinction; 

 but it is difficult to show this, uncomplicated with other 

 variations. The determinations of Kries and Auerbach 

 (XXX. -XXXVIII.) show the result of distinctions of vari- 

 ous kinds, though an analysis of the causes of these differ- 



ences is hardly practicable. It is quite clear that in re-act- 

 ing by the incomplete method the re-action is shorter when 

 the stimulus is the stronger of two intensities than vrhen it 

 is the weaker of the two (XXXVI and XXXVIII.). Berger 

 has also shown that the intensity of the stimulus has some 

 influence upon the distinction time beyond what would be 

 due to the effect upon the simple re-action time therein con- 

 tained. The difference between the corresponding simple 

 and the incomplete re-action to a bright light is 85(7; to a 

 medium light, 119(7; to a weak light, 114(7; while similar 

 differences for adaptive re-actions are 167(7, 179(7, 192(7; the 

 inference being that the intensity of the stimulus affects the 

 distinction rather than the choice. Again (in the series 

 VI. -X.), we find that Cattell recognized most quickly that 

 an expected one of 26 pictures was present, then that one of 

 26 letters, next one of 26 short English words, next one of 

 26 short G-erman words. The differences between the time 

 for recognizing letters and short words is very slight com- 

 pared to the increase in complexity of the impression, and 

 thus shows the effect of practice in recognizing words as a 

 whole. Furthermore, in the series of experiments (partly 

 cited in XLI.-XLIII.) in which one to six place numbers 

 were recognized, while there is a concomitant increase in the 

 number of possible impressions, it seems fair to refer the 

 main increase in time to the increasing complexity of the 

 impression. In passing from the recognition of one to two 

 or of two to three place numbers, the increase in time is 

 slight; but from there on, the increase itself increases with 

 the increase of the number of numerals (53(7, 147(7, 322(7),— 

 a fact probably related to the practice in grasping numbers 

 in groups of threes. Another series (XXIV. -XXiX.) may 

 be mentioned here, and is interesting as indicating that it is 

 more difficult to tell to which of five categories (a city, a 

 river, etc.) a word belongs than what part of speech it is; 

 and this is in turn easier than to tell the sphere of activity 

 of a noted man. It should be noted that the choice, the 

 range of impressions, the connection between impression 

 and movement, the method of re-action, are equivalent in all 

 three experiments; so that the difference is fairly referable 

 to the distinction process involved. We may finally notice 

 as here pertinent the observations of Vintschgau upon the 

 distinguishability of different tastes. He found that by the 

 incomplete method it took longest to re-act to bitter when 

 the alternative was distilled water, next long to sweet, next 

 to sour, and shortest to salt. Similarly, in adaptive re-ac- 

 tions with the two hands to all possible combinations of two 

 of the four tastes, salt was most quickly re-acted (384(7), sour 

 next (397(7), sweet next (409(7), and bitter last (456(7). 



(4) The Foreknowledge of the Subject. Within the re- 

 striction that the foreknowledge of the subject shall be 

 limited to the knowledge of the associative bond between 

 stimulus and movement, there is room for variation. The 

 simplest case would present but one stimulus re-acted to, 

 and but one not re-acted to, or, in the adaptive re-action, but 

 one stimulus for each mode of re-action. In all such cases 

 (I., II., IV., XL, XXXVIII., may be cited as instances) 

 the foreknowledge of the subject presents the maximum of 

 deflniteness. Any departure from these conditions brings 

 with it an increase in the time of reaction. Cattell finds 

 but a very slight increase (5-7(7) in the incomplete re-action 

 when the stimulus not re-acted to, instead of being but a 



