Emergent, untrained stimulus relations in many-to-one matching-to-sample discriminations in rats.
Rats show emergent stimulus relations, proving equivalence learning is a core animal process.
01Research in Context
What this study did
Nakagawa (2005) taught rats to match pictures using many-to-one rules. If three shapes all meant 'same,' the rat learned to pick one lever.
Some rats then saw new sets that kept the rule. Others saw sets that broke it. The team watched who learned the next task faster.
What they found
Rats with steady rules flew through new matches. Their errors dropped fast even though the pictures were brand-new.
Rats with mixed rules stumbled. The stable group showed untrained stimulus relations—evidence of equivalence in rodents.
How this fits with other research
Brown et al. (1994) first proved pigeons can do the same trick. Esho moved the idea to rats, showing the effect is not bird-specific.
Paranczak et al. (2024) later got big, clear equivalence networks in kids after only minutes of training. The rat work gives that clinical leap its lab roots.
Reichow et al. (2011) found kids need arbitrary, unrelated pictures for clean transitive ties. Rats, like children, learn the links best when the items do not look alike.
Why it matters
Equivalence is not just a human language trick; even rats build untrained stimulus classes. For you, this means the process is basic and robust. When you set up conditional-discrimination programs for learners with autism, keep the stimulus classes consistent early on. Stable many-to-one relations now can speed up new, untaught relations later—just like the rats who mastered fresh sets in fewer trials.
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02At a glance
03Original abstract
The present experiment investigated whether rats formed emergent, untrained stimulus relations in many-to-one matching-to-sample discriminations. In Phase 1, rats were trained to match two samples (triangle and horizontal stripes) to a common comparison (horizontal stripes) and two additional samples (circle or vertical stripes) to another comparison (vertical stripes). Then, in Phase 2, the rats were trained to match the one sample (triangle) to a new comparison (black) and the other sample (circle) to another comparison (white). In the Phase 3 test, half the rats (consistent group) were given two new tasks in which the sample-correct comparison relation was consistent with any emergent stimulus relations that previously may have been learned. The remaining 6 rats (inconsistent group) were given two new tasks in which the sample-correct comparison relation was not consistent with any previously learned emergent stimulus relations. Rats in the consistent group showed more accurate performance at the start of Phase 3, and faster learning to criterion in this phase, as compared with rats in the inconsistent group. This finding suggests that rats may form emergent, untrained stimulus relations between the discriminative stimuli in many-to-one matching-to-sample discriminations.
Journal of the experimental analysis of behavior, 2005 · doi:10.1901/jeab.2005.41-04