132 Animal Intelligence 
COMPLEXITY OF ASSOCIATIONS 
An important question, especially if one wishes to rate an 
animal ona scale of intelligence, is the question of how com- 
plex an association it can form. A man can learn that to 
open a door he has to put the key in its hole, turn it, turn 
the knob, and pull the door. Here, then, is a complex act 
connected with the simple sense-impression. Or, con- 
versely, a man knows that when the ringing of a bell is 
followed by a whistle and that by a red light he is to do a 
certain thing, while if any of the three happens alone, he is 
not to. How far, then, we ask, can animals go along the 
line of increased complexity in the associations ? 
We must not mistake for a complex association a series 
of associations, where one sense-impression leads to an act 
such as to present a new sense-impression which leads to 
another act which in its turn leads to a new sense-impression. 
Of the formation of such series animals are capable to a 
very high degree. Chicks from 10 to 25 days old learned to 
go directly through a sort of big labyrinth requiring a series 
of 23 distinct and in some cases fairly difficult associations, 
of which 11 involved choices between two paths. By this 
power of acquiring a long series animals find their way to 
distant feeding grounds and back again. But all such cases 
are examples of the number, not of the complexity, of animal 
associations. 
Some of my boxes were such as did give a chance for a 
complex association to be formed. Such were G (thumb 
latch), J (double), K and L (triples) for the cats, and O (triple) 
for the dogs. It would be possible for a cat, after stepping 
on the platform in K, to notice that the platform was in a 
different position, and so feel then a different sense-impres- 
sion from before, and thus turn the thing into a serial asso- 
