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.

Generalized identity in a successive matching‐to‐sample procedure in rats: Effects of number of exemplars and a masking stimulus

“…However, both these two rats and O2 approached full transfer (probe performance equivalent to baseline) after four exemplars. Overall, these results replicated the high levels of transfer obtained by Prichard et al () and Bruce et al () after training with four exemplars. Transfer of any kind after so few training exemplars is noteworthy as it is in marked contrast to the much larger number generally required to produce even partial transfer in pigeons and monkeys (e.g., Katz & Wright, ).…”

“…Rats generally perform poorly in MTS tasks using visual stimuli (Iverson, 1993(Iverson, , 1997 as control by stimulus location can interfere with relational learning. This seems to be less of a problem when olfactory stimuli are used, as same-different concept learning has been demonstrated in previous studies from our laboratory (e.g., Bruce et al, 2018;Prichard et al, 2015). Alternatively, it may be that fewer exemplars are needed to obtain transfer using successive procedures (e.g., Cook et al, 2003;Urcuioli, 2011).…”

“…Cook, Kelly and Katz (2003) found transfer of samedifferent responding to novel stimuli in pigeons after training with only two exemplars, and above chance generalized identity matching was also observed by Urcuioli (2011) in pigeons after training with only two stimuli. Both of these studies used successive (go, nogo) discrimination procedures, as did the present study and Bruce et al (2018) and Prichard et al (2015) with rats. These findings raise the question of whether some features of the successive procedure might accelerate the development of relational responding.…”

“…One potential cue that might be particularly salient in the present study is control by stimulus change. In the present study (as well as Bruce et al, 2018, andPrichard et al, 2015), the sample odor was presented for 5 s followed by a 1-s interstimulus interval (ISI). On matching trials the ISI was followed by a 5-s presentation of the same odor, but given that there may be a lingering trace of the sample odor, this may have functionally served as an 11-s (or longer) presentation of a single odor which is terminated by a reinforced response.…”

“…After high levels of accuracy were reached with the four trained odors, accuracy on probe tests with four novel odors matched baseline performances. In a more recent study, these surprising results were replicated and extended to a successive NMTS procedure (Bruce et al, ). The present experiments represent an effort to follow up these previous studies with olfactory stimuli in rats.…”