Limitations on environmental control of multiple fixed-ratio behavior.

Eight white rats were trained to make fixed numbers of responses on each of two bars alternately in the presence of different exteroceptive stimuli. Three types of error were observed: alternating-bar switching before response requirements for reinforcement were met; perseverating-responding on the wrong bar after reinforcement; and overshooting-responding on a bar after reinforcement became available. Alternating and perseverating errors occurred mainly on the bar requiring the smaller ratio. When the ratios on the bars were changed, alternating errors were most common, but they diminished rapidly. Perseverating and overshooting errors did not diminish.