other keys in the group. On the completion of a subject's
reaction to the group of three keys, a group of seven keys at the
opposite end of the keyboard may, for example, be presented. Similarly,
the subject is required to discover with the minimum number of trials
the correct reaction-mechanism. Thus, time after time, the experimenter
presents a different group of keys so that the subject in no two
successive trials is making use of the same portion of the keyboard. It
is therefore impossible for him to react to spatial relations in the
ordinary sense and manner, and unless he can perceive and appropriately
respond to the particular relation which constitutes the only constant
characteristic of the correct reaction-mechanism for a particular
problem, he cannot solve the problem, or at least cannot solve it
ideationally and on the basis of a small number of observations or
trials.

For the various infrahuman animals whose ideational behavior has been
studied by means of this method, it has been found eminently
satisfactory to use as reaction-mechanisms a series of similar boxes,
each with an entrance and an exit door. An incentive to the selection of
the right box in a particular test is supplied by food, a small quantity
of which is placed in a covered receptacle beyond the exit door of each
of the boxes. Each time an animal enters a wrong box, it is punished for
its mistake by being confined in that box for a certain period, ranging
from five seconds to as much as two minutes with various individuals or
types of organism. This discourages random, hasty, or careless choices.
When the right box is selected, the exit door is immediately raised,
thus uncovering the food, which serves as a reward. After eating the
food thus provided, the animal, according to training, returns to the
starting point and eagerly awaits an opportunity to attempt once more to
find the reward which it has learned to expect. With this form of the
apparatus, the boxes among which choice may be made are indicated by the
raising (opening) of the front door.

Since with various birds and mammals the box form of apparatus had
proved most satisfactory, I planned the primate apparatus along similar
lines, aiming simply to adapt it to the somewhat different motor
equipment and destructive tendencies of the monkeys. I shall now briefly
describe this apparatus as it was constructed and used in the Montecito
laboratory.

EXPLANATION OF PLATE IV

F