Effects of diazepam and ethanol alone and in combination on conditioned suppression of key-pecking in the pigeon.

Pigeons were intermittently given grain reinforcement for key pecks. Occasional 30-sec keylight changes (warning stimulus) were followed by a brief electric shock, which suppressed responding during the warning stimuli. This suppression was reduced by diazepam and ethanol, yet combinations of the two drugs did not reduce suppression (antagonistic effect). Each drug reduced responding in the absence of the warning stimulus, and combinations of the drug produced still greater reductions in this safe-period responding (synergistic effect).