Intermanual stereognostic size discrimination in split-brain monkeys.

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Abstract
Seven pigtail monkeys were trained to perform an intermanual size discrimination and tested after split-brain surgery. Experiment 1 required [Subjects] Ss to pull the larger of 2 cylindric levers presented simultaneously, 1 by each hand. Postoperative scores for 2 Ss working with 4 lever pairs from 5 sizes were good initially, but declined gradually. Scores of 2 Ss working with 9 lever pairs from 10 sizes fell abruptly to chance level after surgery and remained there. Experiment 2 required Ss to use 1 hand to pull 1 of 2 levers that matched in size a lever presented to the other hand; postoperative scores from 3 Ss were at chance level, even with gross size difference. Evidently cross-communication of manual stereognostic size information was eliminated by the surgery.