Differential reinforcement and stimulus control of not responding.

Pigeons were trained to respond with equal variable-interval reinforcement in the presence of a white key and also a white key with a vertical line. They were then trained not to respond to the vertical line by extinguishing the response or by reinforcing its non-occurrence at various frequencies. During training, the rate of key-pecking in the presence of the white key, maintained by a constant variable-interval schedule of reinforcement, depended on the frequency of reinforcement in the presence of the line. When lines of different orientations were presented in a generalization test, birds trained with extinction responded more to other orientations than to the vertical line, whereas those trained with high frequencies of reinforcement for not responding tended to respond equally at all line orientations. Intermediate frequencies of reinforcement gave mixed results.