Matching- and nonmatching-to-sample concept learning in rats using olfactory stimuli

Abstract

Previous research has shown that rats can learn matching-to-sample relations with olfactory stimuli; however, the specific characteristics of this relational control are unclear. In Experiment 1, 6 rats were trained to either match or nonmatch to sample in a modified operant chamber using common household spices as olfactory stimuli. After matching or nonmatching training with 10 exemplars, the contingencies were reversed with five new stimuli such that subjects trained on matching were shifted to nonmatching and vice versa. Following these reversed contingencies, the effects of the original training persisted for many trials with new exemplars. In Experiment 2, 9 rats were trained with matching procedures in an arena that provided for 18 different spatial locations for comparison stimuli. Five subjects were trained with differential reinforcement outcomes and 4 with only one type of reinforcer. Differential outcomes and multiple exemplars facilitated learning, and there was strong evidence for generalization to new stimuli for most rats that acquired several conditional discriminations. Performances with novel samples were generally above chance, but rarely reached the high levels obtained during baseline with well-trained stimulus relations. However, taken together, the data from the two experiments extend previous work, show that rats can learn both match and nonmatch relations with different experimental protocols, and demonstrate generalization to novel sample stimuli.

Keywords: abstract concepts; identity; matching-to-sample; oddity; rats; reversal learning.

Fig 1

Percent correct responding for subjects in Experiment 1 initially trained on MTS, then reversed to NMTS. Bracketed percentages in panels 2 and 3 for each subject represent outcomes on the initial trials in which each novel stimulus served as a sample during that phase.

Fig 2

Percent correct responding for subjects in Experiment 1 initially trained on NMTS, then reversed to MTS. Bracketed percentages in panels 2 and 3 for each subject represent outcomes on the initial trials in which each novel stimulus served as a sample during that phase.

Fig 3

Odor arena apparatus showing 18 hole positions designed to hold comparison stimulus cups.

Fig 4

Session-by-session accuracies across all training sets for subjects F3 and H7 (both trained with differential outcomes, DO). Panel labels depict phases of the study with different stimulus sets and horizontal line shows criterion level performance.

Fig 5

Session-by-session accuracies across all training sets for subjects G13 (DO) and F6 (sucrose only). Panel labels depict phases of the study with different stimulus sets and horizontal line shows criterion level performance.

Fig 6

Session-by-session accuracies across all training sets for subjects G8 and J6 (DO). Panel labels depict phases of the study with different stimulus sets and horizontal line shows criterion level performance.

Fig 7

Percent correct on novel-sample trials (open symbols, left vertical axis) and number of sessions to criterion (closed symbols, right vertical axis) are plotted as a function of the number of exemplars as training progressed in Experiment 2. The top panel shows subjects with approximately 40 total sessions (F3 and H7), the middle panel shows the same function for subjects with approximately 60 total sessions (G13 and F6), and the lower panel for subjects with approximately 100 total sessions (G8 and J6).

Fig 8

Mean percent correct is plotted for the criterion baseline sessions (two phases for F6, F3, H7 and three phases for G13 and G8) alongside the criterion probe and novel combination accuracies (i.e., generalized matching performance).