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130 Animal Intelligence 



former signal and fed the cats, sometimes the latter and did 

 not. The object was to see how long the cat would be in 

 learning always to go up when I gave the first, never to do 

 so when I gave the second signal. I said the words in both 

 cases as I naturally would do, so that there was a difference 

 in emphasis and tone as well as in the mere nature of the 

 syllables. The two signals were given in all sorts of com- 

 binations so that there was no regularity in the recurrence of 

 either which might aid the animal. The cat at first did 

 not always climb up at the first signal and often did climb 

 up at the wrong one. The change from this condition to 

 one of perfect discrimination is shown in the accompanying 



curves (Fig. 22), one show- 

 ing the decrease in fail- 

 ures to respond to the 

 l % wrong signal. The first 



FlG - 22 - curve is formed by a line 



joining the tops of perpendiculars erected at intervals of 

 i mm. along the abscissa. The height of a perpendicular 

 represents the number of times the cat failed to respond 

 to the food-signal in 20 trials, a height of i mm. being the 

 representative of one failure. Thus, the entire curve 

 stands for 280 trials, there being no failures after 60 trials, 

 and only i after the 4oth. 



In the other curve, also, each i mm. along the abscissa 

 stands for 20 trials, and the perpendiculars whose tops the 

 curve unites represent the number of times the cat in each 

 20 did climb up at the signal which meant no food. It will 

 be seen that 380 experiences were necessary before the an- 

 imal learned that the second signal was different from the 

 first. The experiment shows beautifully the animal method 

 of acquisition. If at any stage the animal could have 

 isolated the two ideas of the two sense-impressions, and felt 



