88 BIOLOGICAL LECTURES. 



two signals were given in all sorts of combinations, 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, one showing the decrease 

 \\\ failures to respond to the right signal, the other showing the 

 decrease in responses to the wrong signal. The first curve 



is formed by a line joining the 

 tops of perpendiculars erected at 

 intervals of I mm. along the ab- 

 FIG scissa. The height of a perpen- 



dicular 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 animal 

 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 them together in comparison, 

 this long and tedious process would have been unnecessary." 1 



By a complex association I mean an association where either 

 situation or act (or both) is a compound. A man can learn 

 that to open a door he has to put the key in the hole, turn it, 

 turn the knob, and pull the door. Or, conversely, a man can 

 learn that when the sound of a bell is followed by a whistle, 

 and that by a blue light, a certain act is in place, while if any 

 one of the three comes alone it is not. In the first case, the 

 act is a complex of several ; in the second case, the situation. 



1 Animal Intelligence, an Experimental Study of the Associative Processes 

 in Animals, pp. 87-90. 



