_Problem 4. Middle_

As the available time for the continuation of the experiment was
limited, it was decided to proceed with work on problem 4 immediately
upon the completion of problem 3, and on July 20, the problem of the
middle door was presented to Sobke. Since it was anticipated that this
sudden change would confuse and discourage him greatly, the only form of
punishment administered was the momentary lowering of the entrance door
of the wrong box. As in the previous problem, he was aided after ten
successive wrong choices. As might have been anticipated, he
persistently entered the end boxes of the groups, and this in some
instances probably would have been kept up for many minutes had not the
experimenter lured him into the right box by slightly raising the exit
door. In the first series, he had to be aided in five of the ten trials.
The total time for the series was forty-five minutes, the total number
of choices, eighty-eight. In the second series, he was aided in four of
the trials. The total time required was seventy-two minutes, and the
total number of choices was seventy-six.

Throughout the first series, Sobke worked hard, but with evidently
increasing dissatisfaction. He clung persistently to his acquired
tendency to choose the end boxes, and after each trial he returned less
willingly to the starting point. Up to this time his attitude toward the
experimenter had been perfectly friendly, if not wholly trustful. But
when on July 21 he was brought into the apparatus for the second series,
he exhibited a wholly new form of behavior, for instead of attending
diligently to the open doors and devoting his energies to trying to find
the right box, he instead, after gazing at them for a few seconds,
turned toward the experimenter and jumped for him savagely, throwing