196 Animal Intelligence 



the two signals and associates with them ideas of 'food' 

 and 'no food,' 'go down' and 'stay still,' and uses these 

 ideas to control his conduct, he will, we have a right to 

 expect, change suddenly from total failure to differentiate 

 the signals to total success. He will or won't have the ideas, 

 and will behave accordingly. The same result could, of 

 course, be brought about by very rapid association of the 

 new signal with the act of keeping still, a very rapid in- 

 hibition of the act of going down in response to it by virtue 

 of the lack of any pleasure from doing so. 



For convenience I shall call the signals after which food 

 was given yes signals and those after which food was not 

 given no signals. Signals not described in the text are 

 shown in Fig. 29, below. The progress of the monkeys in 



3 (02 ft 106 8 108 



Y b. n u 



3 103 6 106 8 109 



T K - 



* 104 7 107 1 101 



1110 



FIG. 29. 



discriminating is shown by Figs. 30 and 31, on pages 199 

 and 201. In Figs. 30 and 31 every millimeter along the 

 horizontal or base line represents 10 trials with the signal. 

 The heights of the black surface represent the percentages 

 of wrong responses, 10 mm. meaning 100 per cent of 



