Discrimination of highly similar stimuli as members of different equivalence classes
Show similar comparison stimuli side-by-side, not one after another, or learners may never link them into an equivalence class.
01Research in Context
What this study did
Ayres‐Pereira et al. (2025) asked 24 college students to learn three-member equivalence classes.
The pictures were almost twins: same shape, color, and size with only a tiny line different.
Each person got the same AB/AC conditional-discrimination lessons, but the way the choices appeared changed across phases: side-by-side, one-by-one, or sample-only.
What they found
When the near-identical comparisons sat next to each other, every adult formed the classes.
In every other layout—sequential or sample-only—zero adults passed the final tests.
A simple switch in display timing made the difference between 100 % and 0 % success.
How this fits with other research
Weissman-Fogel et al. (2015) and Fields et al. (2012) already showed that adding a meaningful photo or pre-training extra relations can push success from about 17 % to 60 %.
The new study keeps the stimuli abstract and meaningless, yet hits 100 %—proof that display arrangement can beat the meaningful-stimulus boost.
Guerrero et al. (2021) used easy auditory–visual pairs first, then moved to hard visual-only words; their tactic and the present one both front-load salience, just through different routes.
Collier et al. (1986) warned that where a stimulus sits can become part of the cue; here we see that when it appears matters just as much.
Why it matters
If you teach conditional discriminations with look-alike icons, flashcards, or PECS symbols, line up the choices at the same time.
Skip slow serial presentation or sample-only drills—they can block equivalence before it starts.
One quick layout tweak may save weeks of extra teaching.
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02At a glance
03Original abstract
Learning to discriminate between physically similar stimuli as members of different classes can be relevant in certain situations. This study investigated effective methods of displaying two pairs of quasi‐identical stimuli, as samples and/or comparisons, during the training of baseline conditional discriminations. The goal was to enable participants to form three 3‐member equivalence classes and discriminate similar stimuli as members of distinct equivalence classes. Eighteen adults underwent arbitrary relations (AB/AC) training. A multiple‐probe design assessed maintenance and emergence of stimulus relations. Participants were randomly assigned to one of six training conditions across three experiments. Conditions 1, 2, and 5 presented quasi‐identical stimuli successively as samples during training. Condition 3 presented quasi‐identical stimuli successively as comparisons, whereas Condition 4 presented quasi‐identical stimuli simultaneously as comparisons. Condition 6 presented each pair of quasi‐identical stimuli simultaneously as a sample and a comparison. Condition 4 uniquely resulted in successful equivalence class formation for all participants. Conditions 3 and 6 failed to form equivalence classes, whereas Conditions 1, 2, and 5 did not yield baseline learning. These findings highlight the relevance of presenting quasi‐identical stimuli as simultaneous comparisons (Condition 4) to foster equivalence class formation. Understanding optimal training conditions has implications for discussions on the acquisition of simple discriminations required in training simultaneous conditional discriminations.
Journal of the Experimental Analysis of Behavior, 2025 · doi:10.1002/jeab.4230