Jtilt 31, 1908] 



SCIENCE 



153 



found to hold approximately for tie bright- 

 ness vision of this animal. (The discussion 

 leading up to the demonstration of Weber's 

 law is prolix and not clearly written.) The 

 results of the tests on the color vision of the 

 dancer make it somewhat problematical as 

 regards whether this form has the power to 

 discriminate between chromatic stimulations 

 on the basis of wave-length alone. The author 

 thinks that there is some evidence at hand to 

 show that the mouse differentiates the red end 

 of the spectrimi from the other regions. The 

 red end of the spectrum seems to have a low 

 stimulating effect. Whether this is true in 

 the case of other mammals or not remains for 

 further tests to decide. The experimental 

 demonstration of the fact is difficult to make. 

 The safest test to make, it seems to the re- 

 viewer, is to determine the reaction threshold 

 of the animal to all the hues of the spectrum 

 and on the basis of these determinations to 

 construct the luminosity curve of the dancer's 

 spectrum. The calibration of the white value 

 of such minimal chromatic stimulations would 

 be exceedingly difficult. The fact is dwelt 

 upon at some length, because if it is true that 

 the luminosity curve is different in different 

 animals (and different even from that of the 

 totally color-blind human being), then the in- 

 ference that equality of brightness of certain 

 hues in man means equality of brightness of 

 those same hues in animals has no basis in 

 fact. The results which Yerkes presents, 

 however, make it extremely problematical 

 whether any other investigator up to Yerkes 

 has ever touched the problem of color vision 

 in animals. 



In the chapter on the role of sight in the 

 daily life of the dancer, Yerkes makes tests 

 to determine the relative importance of the 

 various senses which are employed in learning 

 the maze. The maze affords an almost ideal 

 form of problem for this purpose. It offers 

 control of the sensory-motor adjustments 

 without at the same time introducing difficul- 

 ties which are unsuited to the motor capaci- 

 ties of the animal. In learning the labyrinth, 

 the author states : " It is safe to say, then, 

 that under ordinary canditions habit forma- 

 tion in the dancer is conditioned by the use 



of sight, touch and smell, but that these senses 

 are of extremely different degrees of impor- 

 tance in different individuals." The reviewer 

 feels that this conclusion is not well grounded 

 in experimentation. To his mind at least, 

 Yerkes has not shown how and to what degree 

 vision, smell and contact stimulations are 

 essential factors in learning the maze. Such 

 impressions, while possibly assailing the ani- 

 mal at every turn in the maze, might be as 

 wholly extraneous to the learning process as 

 is the impression of the flying bird to the 

 hound hot upon the scent of his chosen 

 quarry. 



Under habit formation, Yerkes takes up in 

 detail the dancer's ability to learn various 

 forms of labyrinths, to climb ladders and to 

 form discrimination habits ^white-black). A 

 satisfactory account of the learning process as 

 a whole is given. Tables of times, errors, etc., 

 are appended so that the learning processes of 

 the dancer can be compared with those of 

 other animals. Indeed, Yerkes's method of 

 presentation might well serve as a guide for 

 the work of future investigators who may 

 deal with this part of the field of behavior. 

 There is need all through our work of stand- 

 ard apparatus and standard methods of ex- 

 perimentation as well as of conventionalized 

 forms of presentation of results. 



It is of interest to note that the dancer's 

 method of learning is one of trial and error; 

 there is no tendency on the part of one animal 

 to imitate the acts of another. Putting the 

 dancer through does, however, seem to hasten 

 the formation of an association. 



An interesting account is given of the effi- 

 ciency of training methods. Shall we give 

 an animal at work upon, e. g., the white-black 

 discrimination test, two, ten, twenty or more 

 trials per day? The index of efficiency is 

 given as follows: 



For 2-5 trials per day 81.7 ± 2.7 



For 10 trial* per day 88.0 ± 4.1 



For 20 trials per day 91.0 ± 5.3 



Continuous test 170.0 ± 4.8 



Yerkes suggests that it would be interesting 

 to compare the efficiency of training methods 

 in terms of the duration of the habit. This 



