The effect of intertrial interval food presentions on pigeons' delayed matching to sample accuracy

Parallel effects of temporal variables on autoshaping and on delayed matching to sample performance suggest that delayed matching, like autoshaping, might depend upon the within-trial expectancy of reinforcement relative to the overall expectancy of reinforcement in the session. This possibility was assessed by presenting free food at different times during a 30-sec intertrial interval (ITI) in a delayed matching to sample procedure with pigeons. In three conditions a single free food presentation occurred, either early, mid-way, or late in each ITI; in another condition, three food presentations occurred during each ITI, one at each time location. Relative to a baseline condition, in which free food never occurred during the ITI, only food presentations late in the ITI produced a significant disruption in accuracy, and this effect occurred only at the longest of three delays tested. Three free food presentations in each ITI disrupted accuracy only to the same degree as a single, late, ITI food presentation. Thus, accuracy was affected by the temporal location rather than the frequency of ITI food presentations. These effects appear to differ from those of ITI food presentations on autoshaping and do not seem to be understandable in terms of changes in the background expectancy of reinforcement. It was suggested instead that food presented late in the ITI might disrupt subsequent memory processes.