The basis of solution by chimpanzees of the intermediate size problem.

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Abstract
The basis of differential response by chimpanzees to the intermediate member of 3 different-sized squares was investigated. After learning to choose the medium-sized of 3 squares (e.g., 256 sq. cms. in the stimulus combination 409, 256, 160), the chimpanzees continued to choose the same (absolute) stimulus when it was no longer the intermediate member of a new test combination, e.g., 256, 160, 100. Reversal training to the intermediate member of the test combination led to some evidence on the part of 2 of the 6 subjects of limited response on a configurational basis. The remaining 4 subjects continued to respond definitely on an absolute basis. The results are shown to support the writer''s "absolute" type of theory of transposition and to contradict, insofar as it is possible to do so, the Gestalt and relational interpretations.