THE ROLE OF EXPERIMENTER-ODOR CUES IN THE PERFORMANCE OF OBJECT-MEMORY TASKS BY RATS

Two experiments assessed whether odors left on stimulus objects by exp erimenters who handle them might confound the interpretation of ostens ibly visually guided object-memory tasks for rats. In Experiment I, ra ts were able to discriminate the relative recency with which an experi menter touched two otherwise identical objects (intertouch interval = 4 sec), presumably on the basis of an odor-intensity discrimination. H owever, after the rats mastered the odor discrimination with no delay between when the second of the two stimulus objects was last touched b y the experimenter and when the rats were permitted to attempt the dis crimination, their performance dropped to chance levels when this dela y was increased to 15 sec. In Experiment 2, rats were trained in two s lightly different ways to perform a delayed-nonmatching-to-sample (DNM S) task, one that involved systematic differences in the temporal orde r in which the experimenter handled the sample and novel stimulus obje cts and one that did not. There were no significant differences in the rate at which rats mastered the DNMS task with these two procedures, and the performance of rats that were trained according to the former procedure was unaffected when they were switched to the latter procedu re. Moreover, rats required considerably fewer trials to master the DN MS task than the rats in Experiment I required to master the odor disc rimination. These findings demonstrate that, under certain circumstanc es, rats can discriminate the relative recency with which two objects are handled by an experimenter, but that this ability contributes litt le to their performance of conventional object-based DNMS tasks.