This or not that: select and reject control of relational responding in rats using a blank comparison procedure with odor stimuli.

The blank comparison (BLC) task was developed to assess stimulus relations in discrimination learning; that is, are subjects learning to "select" the correct stimulus (S+) or "reject" the incorrect stimulus (S-) or both? This task has been used to study exclusion learning, mostly in humans and monkeys, and the present study extends the procedure to rats. The BLC task uses an ambiguous stimulus (BLC+/-) that replaces S+ (in the presence of S-) and replaces S- (in the presence of S+). In the current experiment, four rats were trained to remove session-novel scented lids from sand-filled cups in a two-choice, simultaneous presentation procedure called the Odor Span Task (OST) before being trained on the BLC procedure using odors as the discriminative stimuli.

Functional equivalence classes in rats: Repeated olfactory discrimination reversals and delayed stimulus probes.

The simultaneous matching-to-sample procedures that are widely used to study stimulus equivalence in human participants have generally been unsuccessful in animals. However, functional equivalence classes have been demonstrated in pigeons and sea lions using a concurrent repeated reversal discrimination procedure. In this procedure, responding to one set of stimuli is reinforced but responding to a different set is not and the set associated with reinforcement is changed with multiple reversals during the experiment.

Generalized, cross-modal, and incrementing non-matching-to-sample in rats.

Same/different concept learning has been demonstrated in previous research in rats using matching- and non-matching-to-sample procedures with olfactory stimuli. In Experiment 1, rats were trained on the non-matching-to-sample procedure with either three-dimensional (3D plastic objects; n = 3) or olfactory (household spices, n = 5) stimuli, then tested for transfer to novel stimuli of the same, and then the alternate, modality. While all three rats trained with olfactory stimuli showed generalized non-matching to novel odors, only one rat learned the 3D relation and showed generalized transfer to novel objects.

Incrementing non-matching- but not matching-to-sample is rapidly learned in an automated version of the odor span task.

The odor span task (OST) is frequently used to assess memory capacity in rodents. Odor stimuli are presented in a large arena and choices of session-novel odors produce food reward. The procedure can be described as an incrementing non-matching-to-sample contingency because on each trial one new stimulus is presented along with one or more previously presented (non-reinforced) comparison odors.

Repeated reversals of concurrent olfactory discriminations in rats: A search for functional equivalence.

Equivalence class formation has been difficult to demonstrate in nonhumans, but one method that has been successful is a simple discrimination procedure in which contingencies associated with two sets of arbitrary discriminative stimuli are repeatedly reversed. Pigeons and sea lions shift responding after encountering the newly-reversed contingency with only a few set members, showing evidence of functional equivalence. We used this strategy to determine whether similar findings would occur in rats using olfactory stimuli.