Monkeys Driven by Non-Biological Intrinsic Drive

Topic: Motivation Sources
Researchers: Harry F. Harlow (Professor of Psychology, University of Wisconsin, US), Margaret Kuenne Harlow, and Donald R. Meyer.
Published At: Journal of Experimental Psychology
Year: 1949
Formal Reference: Harry F. Harlow, Margaret Kuenne Harlow, and Donald R. Meyer, “Learning Motivated by Manipulation Drive”, Journal of Experimental Psychology 40 (1950), 228-234
Main Conclusion: There is a 3rd drive: the performance of a task provided intrinsic reward, and this 3rd drive is not inferior to the 1st and the 2nd drives.

Description of Experiment
a. Eight rhesus monkeys gathered for a two-week experiment on learning. The following puzzle was placed in the monkeys’ cages:

b. The monkeys immediately began to play with the puzzle.
c. On days 13 and 14 of the experiment, the monkeys solved the puzzle two-thirds of the time in less than 60 seconds.
d. At no point of the experiment, nobody taught the monkeys how to solve the puzzle, nobody rewarded the monkeys for solving the puzzle in any way (neither food, affection nor applause).
e. Then the monkeys were rewarded with raisins for solving the puzzle, but they consequently made more errors and solved the puzzle less frequently.

Scientists then knew of two main drives powering behavior: 1) intrinsic biological drives, like food, drink and sex; 2) external drives stemming from reward & punishment.
In the first section of this experiment (a.-d. above), neither of these two known drives explains the monkeys’ behavior (of solving the puzzle).
The researchers called this 3rd drive “intrinsic motivation”.  I.e. the performance of a task provided intrinsic reward; the monkeys solved the puzzle simply because they found it gratifying to solve the puzzle; they enjoyed it; the joy of the task was its own reward.
The introduction of a reward relevant for the 1st and the 2nd known motivation drivers (e. above) did not improve performance; in fact, it damaged the monkeys performance (more errors, puzzle solved less frequently).