[Illustration:  FIGURE 19.—­Error curves of learning for the solution of problem 2 (second box from right end).]

Problem 3.  Alternately First at Left and First at Right

Following the control series given in connection with problem 1, an interval of rest lasting from August 12 to August 19 was allowed in order that Skirrl might in part at least lose the effects of his training and regain his customary interest in the apparatus by being allowed to obtain food easily instead of by dint of hard labor,—­labor which was harder by far, apparently, than physical activity because it demanded of the animal certain mental processes which were either lacking or but imperfectly functional.  The difficultness of the daily tasks appears to be reliably indicated by the tendency to yawn.

Systematic work on problem 3, which has been defined as alternately the first door at the left and the first door at the right of the group, was begun August 19, and for nine days a single series of ten trials per day was given.  Work then had to cease because of the experimenter’s return to Cambridge.

The results of the work on this problem demand but brief analysis and comment.  The expected ratio of one right to four wrong choices per series appears (see table 3) for the first series of trials, and this in spite of the fact that Skirrl had been trained for several weeks to choose the second door from the right end.  One would ordinarily have predicted a much larger number of incorrect choices.  The right choices were due to the monkey’s strong tendency to go first to the first door at the right and thence to the one next to it.  Indeed in the series given on August 24; this method was followed without variation.  In other words, in every one of the ten trials Skirrl entered first the box at the extreme right end of the group.  This necessarily resulted in as many right as wrong first choices.  Consequently, the ratio reads 1 to 1.  But the method was not adhered to, and at no time either before or after that date did he succeed in equalling this achievement.  There was, as a matter of fact, no steady improvement, and so far as one may judge from the records which were obtained, the course of events in the solution of this problem would have been similar to those in problem 2.

TABLE 3

Results for Skirrl, P. irus, in Problem 3

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 Date | No. of | S.1 | S.2 | S.3 | S.4 | S.5 | S.6 | S.7 | S.8 | S.9 | S.10 | R | W | R | W |Ratio of
        | trials | 5.6.7 | 5.6.7 | 1.2.3.4.5.6 | 1.2.3.4.5.6 | 4.5.6.7.8 | 4.5.6.7.8 | 2.3.4.5