Pigeons perform poorly on a midsession reversal task without rigid temporal regularity

Animals make surprising anticipatory and perseverative errors when faced with a midsession reversal of reinforcer contingencies on a choice task with highly predictable stimulus-time relationships. In the current study, we asked whether pigeons would anticipate changes in reinforcement when the reinforcer contingencies for each stimulus were not fixed in time. We compared the responses of pigeons on a simultaneous choice task when the initially correct stimulus was randomized or alternated across sessions. Pigeons showed more errors overall compared with the typical results of a standard midsession reversal procedure, and they did not show the typical anticipatory errors prior to the contingency reversal. Probe tests that manipulated the spacing between trials also suggested that timing of the session exerted little control of pigeons' behavior. The temporal structure of the experimental session thus appears to be an important determinant for animals' use of time in midsession reversal procedures.