Overt activity during conditioned suppression: a search for punishment artifacts.

Pigeons, previously trained to peck a key (using food as the reinforcer), were permitted unlimited access to food and, concurrently, key pecking was allowed to go unreinforced until all pecking ceased. A tone ending with electrical shock was then repeatedly presented in an effort to establish the tone as a potentially suppressing stimulus. When key pecking was later reestablished, tone presentation (without shock) sharply reduced the rate of pecks. At selected points throughout the experiment, special observation procedures supplemented the recordings of key pecks and provided detailed fine-grain protocols of the birds' overt movements during the periods before, during, and after tone presentations. Results indicated that neither punishment of key pecks nor punishment of other overt movements was a necessary precursor to the conditioned suppression observed in the final stage. As such, the findings support interpretations of conditioned suppression that characterize the phenomenon as reflecting a conditioned emotional reaction that either directly or indirectly inhibits overt activity.