Yerkes, The Sense of Hearing in Frogs. 293 



The two series of reactions of Table I, chosen at random 

 from several hundred, will serve to indicate the method 

 of recording the results as well as the nature of the results 

 themselves. The first ten pairs of reactions fairly represent the 

 variableness of the reactions; the second show still more clearly 

 the influence of the auditory stimulus. 



The results obtained with four frogs, two males (Nos. i 

 and 3) and two females (Nos. 2 and 4) will suffice to indicate 

 the influence of sounds on tactual reactions. For each of the 

 four frogs fifty pairs of reactions were taken in series, and that 

 for each of seven different temporal relations of the two stimuli. 

 The individual averages therefore are based upon fifty reactions, 

 and the total number of reactions for each individual is seven 

 hundred. As is clear from column one of Table II, the tem- 

 poral relations of the stimuli ranged from simultaneity to .9" 

 (i. e., the auditory preceded the tactual by .9"). 



The influence of the sound, which for these experiments 

 was a sudden hammer blow, is discovered by direct comparison 

 of the tactual reaction of each pair with its corresponding audi- 

 tory-tactual reaction. When the tactual reaction is the greater, 

 we infer that the sound has partially inhibited reaction ; 

 when it is the smaller, that it has reinforced reaction ; when the 

 two are equal, that it has been without influence. The influ- 

 ence of sound may be expressed either in terms of the number 

 of reactions reinforced, inhibited and equal, or in terms of the 

 amount of reinforcement or inhibition. Both methods have 

 been employed. Table II presents the percentage value of the 

 auditory-tactual reactions in comparison with the tactual, and 

 also the number of reactions over half which were reinforced or 

 inhibited, while Figures 5 and 6 graphically represent the 

 amount of influence in terms of the tactual reaction. The audi- 

 tory-tactual reaction is always expressed as so many per cent 

 greater (+ i. e., reinforcement) or less ( — i. e., inhibition) than 

 the tactual. In the table + always indicates reinforcement, — in- 

 hibition, and in the curves the portions above the zero line indi- 

 cate reinforcement, those below it inhibition. The number of 

 reactions over half, that is over twenty five, since there were 



