The roles of expectancy and aftereffects in alternation

In each of three experiments rats were pretreated in straight alleys to discriminate the brightness of an alley as signal for the magnitude of reward. Then the rats were tested in E-shaped mazes in which reward varied across trials and in which the brightness of the stem signaled the magnitude of reward. In all three experiments the rats alternated more on trials following a small reward on the previous trial, and in the third experiment the rats alternated more on those trials where a small reward was signaled. Rats choice responses on Trial n were also affected by the stimulus/reward and choice on Trial n − 2 and by the relationship between stimuli/rewards on Trials n − 2 and n. These results were interpreted as a tendency by the rat to change a less satisfactory situation by varying its response, and to retain a more satisfactory situation by perseverating in its choice response.