144 Animal Intelligence 
it jumped to B and, after a similar process, to C. After 
enough trials it forms the habit and when put on A goes 
immediately to B, then 
to C and down. Now 
if, after 75 or 80 trials, 
B you take away the 
| screens, giving the chick 
D a free chance to go to D 
| from either A or B, and 
. then put it on A, the 
following phenomenon 
appears. The chick goes 
up to the edge, looks over, walks up and down it for a while, 
still looking down at the chicks below, and then goes and 
jumps to B as habit has taughtit todo. The same actions 
take place on B. No matter how clearly the chick sees 
the chance to jump to D, it doesnot doso. Theimpulse has 
been truly inhibited. It is not the mere habit of going the 
other way, but the impossibility of going that way. In one 
case I observed a chick in whom the instinct was all but, yet 
not quite, inhibited. When tried without the screen, it went 
up to the edge to look over nine times, and at last, after 
seven minutes, did jump straight down. 
Fic. 23. 
ATTENTION 
I have presupposed throughout one function which it 
will be well to now recognize explicitly, attention.| As 
usual, attention emphasizes and facilitates the process 
which it accompanies.(" Unless the sense-impression is 
- focussed by attention, it will not be associated with the 
, act which comes later) Unless two differing boxes are at- 
tended to, there will be no difference in the reactions to 
