Identity matching-to-sample with olfactory stimuli in rats.
Rats can learn to match new smells after only four training odors, giving us a quick animal model for stimulus-equivalence work.
01Research in Context
What this study did
Four rats learned to match smells. If the sample odor was rose, they had to pick the rose comparison. If it was lemon, they picked lemon.
The rats sniffed the sample, then chose between two odors. Correct choices earned food. After training with four smells, new smells were added to see if the skill would carry over.
What they found
Every rat scored above 90 % with the trained odors. When new smells appeared, they still picked the matching odor more often than chance.
The animals had learned a rule: pick the same smell, not just memorize pairs.
How this fits with other research
Iversen (1993) first showed rats can do identity matching with lights and nose keys. Peña et al. (2006) proved the same rule works when the cues are smells instead of sights.
Galizio et al. (2018) later used a slightly different setup—successive instead of simultaneous presentation—and still got the same strong result. The finding holds even when a masking odor tries to confuse the rats.
Richardson et al. (2025) moved one step further. They used smell cues to build whole equivalence classes, not just single matches. Together these studies trace a line: rats can master simple identity matching and, with more training, expand to full stimulus classes.
Why it matters
If you work on stimulus equivalence, this rat model gives you a fast, cheap way to test new procedures before trying them with people. Swap in smells, skip lengthy verbal instructions, and still get reliable generalized matching. Next time you pilot a protocol, consider olfactory cues and a non-human subject first—it could save hours of troubleshooting later.
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02At a glance
03Original abstract
Identity matching-to-sample has been difficult to demonstrate in rats, but most studies have used visual stimuli. There is evidence that rats can acquire complex forms of olfactory stimulus control, and the present study explored the possibility that identity matching might be facilitated in rats if olfactory stimuli were used. Four rats were trained on an identity match-to-sample procedure with odorants mixed in cups of sand as stimuli. Digging in the sample cup produced two comparison cups, and digging in the comparison cup that contained the same scent as the sample was reinforced. When criterion accuracy levels were reached, novel stimuli were added to the baseline training regimen. All 4 rats reached terminal performance of above 90% correct matching with more than 20 different baseline stimuli and matched novel stimulus combinations with above-chance accuracy; 3 of the 4 rats matched novel stimuli at levels significantly above chance. Accurate matching performance was demonstrated both with 2- and 3-comparison procedures. These results suggest that generalized matching-to-sample can be observed in rats when olfactory stimuli are used and, furthermore, that multiple-exemplar training may be important for its emergence.
Journal of the experimental analysis of behavior, 2006 · doi:10.1901/jeab.2006.111-04