In separate experiments four monkeys and eight pigeons were presented with displays containing one red and two green keys and displays containing three green keys. During feature-positive phases, responses to displays containing the one red and two green keys were reinforced on a fixed-ratio schedule, while responses to displays containing the three green keys were never reinforced. During feature-negative phases, only responses to the three green key displays were reinforced. For monkeys in Experiment 1, both between and within subject analyses indicated that the learning of feature-positive discriminations was superior to the learning of feature-negative discriminations. The within subject analysis further revealed that performance on a feature-positive discrimination was retarded following exposure to a feature-negative discrimination, while performance on a feature-negative discrimination was enhanced following exposure to a feature-positive discrimination. Experiment 2 replicated the essential aspects of these reversal effects in four experimental pigeons. Evidence that these reversal effects were not simply a function of time was provided by four control birds exposed to only a feature-positive or feature-negative discrimination.

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