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 xo signals. Signals not described in the text are 
shown in Fig. 29, below. The progress of the monkeys in 
<i 
A sy 
= 
= 
Fic. 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 
