Sea lions and equivalence: expanding classes by exclusion.
Use exclusion trials to add new stimuli to existing equivalence classes in minutes, not hours.
01Research in Context
What this study did
Kastak et al. (2002) worked with two sea lions. Each animal already had ten pictures that all meant the same thing.
The team showed a new picture next to an old one. The sea lions had to pick the new item by ruling out the known one. This is called exclusion.
After only a few trials, the new picture joined the old group. Later tests proved the animal truly treated it as a class member.
What they found
Exclusion trials quickly grew the set. One session was enough to add a fresh stimulus to a ten-member class.
Follow-up probes showed the new item worked exactly like the original ten. The sea lions picked it in every test without extra teaching.
How this fits with other research
Rojahn et al. (1994) and Roche et al. (1997) showed that once a class forms, any feeling tied to one member spreads to the rest. Reichmuth adds a shortcut: you can slip brand-new stimuli into that same web using simple rejection trials.
Shimizu (2006) stretched equivalence further by letting mouse movements join classes. Together with Reichmuth, the line is clear: classes can grow by adding new stimuli or even new response forms.
Minster et al. (2011) later argued that links form through stimulus correlation, not reinforcement. Their data do not fight Reichmuth’s; they simply offer a different why behind the same growing network.
Why it matters
You can save hours by using exclusion to enlarge stimulus sets. After a learner masters a few pictures, words, or sounds, pair a novel item with a known one and let rejection do the teaching. Check with transfer probes, then move on. This keeps sessions short and curricula lean.
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02At a glance
03Original abstract
Experiments have shown that human and nonhuman subjects are capable of performing new arbitrary stimulus-stimulus relations without error. When subjects that are experienced with matching-to-sample procedures are presented with a novel sample, a novel comparison, and a familiar comparison, most respond by correctly selecting the novel comparison in the presence of the new sample. This exclusion paradigm was expanded with two California sea lions that had previously formed two 10-member equivalence classes in a matching-to-sample procedure. Rather than being presented with a novel sample on a given trial, the sea lions were presented with a randomly selected familiar member of one class as the sample. One of the comparisons was a randomly selected familiar member of the alternative class, and the other was a novel stimulus. When required to choose which comparison matched the sample, the subjects reliably rejected the familiar comparison, and instead selected the unfamiliar one. Next, the sea lions were presented with transfer problems that could not be solved by exclusion; they immediately grouped the new stimuli into the appropriate classes. These findings show that exclusion procedures can rapidly generate new stimulus relations that can be used to expand stimulus classes.
Journal of the experimental analysis of behavior, 2002 · doi:10.1901/jeab.2002.78-449