The merger and development of equivalence classes by unreinforced conditional selection of comparison stimuli.
Equivalence classes can knit together even when you stop reinforcing every correct match.
01Research in Context
What this study did
Saunders et al. (1988) asked a simple question. Can separate stimulus classes merge without giving reinforcers for every correct pick?
They ran three small lab experiments. Adults learned conditional discriminations with abstract shapes. Later they saw new trials where a shape from one class appeared with a shape from another class. No praise, no tokens, no food followed the choice.
The task was just to pick the comparison that "went with" the sample. The team watched to see if classes would still knit together.
What they found
Classes merged even though correct selections never earned reinforcement. Participants consistently matched cross-class pairs after only unreinforced probes.
The effect repeated across all three experiments. Once the basic conditional relations were in place, the absence of rewards did not stop equivalence from expanding.
How this fits with other research
Johnson et al. (2014) extends the same merger idea but adds a twist. They linked classes by making shared reinforcers the "node." Some adults merged instantly, others needed brief unreinforced probes, and one never merged. The 2014 study shows that reinforcers can speed things up, yet the 1988 finding still stands: merger can occur with zero ongoing rewards.
Fields et al. (1991) picked up where the 1988 paper left off. After classes merged, participants generalized to brand-new stimuli that looked like any member of the class. Together the two studies form a chain: unreinforced merger first, then broad generalization second.
Marin et al. (2024) sounds like a contradiction. They warn that lab-perfect equivalence may not survive noisy real-world settings. The clash is only skin-deep. Saunders et al. (1988) proved merger is possible under tight controls; Marin urges us to test whether those fragile classes hold when distractions pile up.
Why it matters
You can grow stimulus classes without delivering a reinforcer every time. This frees you from constant token delivery during equivalence probes. Try inserting short, unreinforced matching trials after your baseline training. If the learner keeps picking correctly, you have evidence the network is expanding on its own. Use that moment to introduce new, functionally related materials instead of more tangible rewards.
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02At a glance
03Original abstract
Three experiments assessed the likelihood that subjects with histories of equivalence class development would respond conditionally on new discriminations in the absence of differential consequences for responses. In the first two experiments, two groups of subjects with different experimental histories, but whose performances showed four equivalence classes, responded on trials without explicit reinforcement involving samples from two of the classes and comparisons from the other two classes, in a two-choice matching-to-sample format. Subjects consistently selected a particular comparison in the presence of a particular sample. Subsequent tests showed the emergence of equivalence relations between stimuli from classes linked by the unreinforced conditional selections. Subsequently, in Experiment II, the subjects' responses in the conditional selection trials were reinforced if the selection was reversed from that made previously. Although reversed selection was maintained, 2 of the 3 subjects continued to perform on equivalence relation trials according to their original unreinforced selections. In the third experiment, these 2 subjects responded on a series of conditional discriminations involving three new pairs of sample stimuli and one new pair of comparison stimuli. No explicit reinforcement followed responses on any trial in this experiment. Subsequent tests for equivalence between sample stimuli revealed the development of two equivalence classes.
Journal of the experimental analysis of behavior, 1988 · doi:10.1901/jeab.1988.50-145