Successive odor matching- and non-matching-to-sample in rats: A reversal design

Abstract

There is a growing body of research on matching- and non-matching-to-sample (MTS, NMTS) relations with rats using olfactory stimuli; however, the specific characteristics of this relational control are unclear. In the current study we examine MTS and NMTS in rats with an automated olfactometer using a successive (go, no-go) procedure. Ten rats were trained to either match- or non-match-to-sample with common scents (apple, cinnamon, etc.) as olfactory stimuli. After matching or non-matching training with four odorants, rats were tested for transfer twice with four new odorants on each test. Most rats trained on MTS showed immediate transfer to new stimuli, and most rats trained on NMTS showed full transfer by the second set of new odors. After meeting criterion on the second transfer test, the contingencies were reversed with four new odor stimuli such that subjects trained on matching were shifted to non-matching and vice versa. Following these reversed contingencies, the effects of the original training persisted for many trials with new odorants. These data extend previous studies on same-different concept formation in rats, showing strong generalization requiring few exemplars. The critical role of olfactory stimuli is discussed.

Keywords: Abstract concepts; Identity; Matching-to-sample; Olfaction; Rats; Same-different.

Figure 1

Mean discrimination ratios for the MTS and NMTS groups during the first 10 sessions of initial training, the first three sessions of transfer phases 1 and 2, and the first 10 sessions of the reversal phase for all 10 rats. Error bars indicate standard deviations.

Figure 2

Mean discrimination is presented for the final session of the initial baseline training and the first exposure to novel stimuli during the transfer and reversal phases.

Figure 3

Response rates on positive and negative trial types for subjects trained initially on MTS. The left panel shows baseline performance on the set of odors initially trained (open circles) compared to performance on the first day of transfer phase 1 (filled circles) with performance on the first exposure to the novel trial types depicted (filled triangles) separately. The center panel shows performance on the second set of odors after criterion was met (open circles) compared to performance on the first day of transfer day 2 (filled circles), with performance on the first exposure to the novel trial types depicted (filled triangles) separately. The right panel shows the effects of reversal with the last day of performance on the MTS trained contingencies (open circles) compared to performance on the first day of the reversed contingencies with a set of four novel scents (filled circles), with performance on the first exposure to the novel trial types depicted (filled triangles) separately.

Figure 4

Response rates on positive and negative trial types for subjects trained initially on NMTS. The left panel shows baseline performance on the set of odors initially trained (open circles) compared to performance on the first day of transfer phase 1 (filled circles) with performance on the first exposure to the novel trial types depicted (filled triangles) separately. The center panel shows performance on the second set of odors after criterion was met (open circles) compared to performance on the first day of transfer day 2 (filled circles), with performance on the first exposure to the novel trial types depicted (filled triangles) separately. The right panel shows the effects of reversal with the last day of performance on the NMTS contingencies (open circles) compared to performance on the first day of the reversed contingencies with a set of four novel scents (filled circles), with performance on the first exposure to the novel trial types depicted (filled triangles) separately.