PARTIAL NEGATIVE REINFORCEMENT: FIXED-RATIO ESCAPE.

Rats were unable to sustain performance when eight bar-presses turned off shock (-FR 8). In a second experiment, thirsty rats were able to maintain a moderate response rate when performance on -FR 8 was also reinforced with water. Some rats continued to bar-press on -FR 8 after withdrawal of positive reinforcement, but at a much lower rate. A possible explanation of the results is that during intermittent escape conditioning in a free-responding situation the absence of shock itself acquires aversive properties.