Conditional discrimination and equivalence relations: A theoretical analysis of control by negative stimuli.
Negative stimuli can fake good equivalence scores, so probe who is really in charge of the pick.
01Research in Context
What this study did
Miranda-Linné et al. (1992) wrote a theory paper. They asked how the wrong picture might guide choices during equivalence tests.
They used math-style proofs. The goal was to warn testers about hidden stimulus control.
What they found
The model showed that the non-matched picture can steer the pick. If it does, symmetry and transitivity scores look fine even when the learner never truly linked the two correct pictures.
The paper lists safeguards. Add extra trials. Watch which picture the learner actually looks at.
How this fits with other research
Perez et al. (2020) ran the test. They blocked the view of the correct picture on some trials. Errors on transitivity and equivalence jumped, just as F et al. predicted. This lab study extends the 1992 warning into real data.
Blough (1980) had already said accuracy alone can fool you. F et al. zoomed in on one reason why: control by the negative stimulus.
Mace et al. (1990) showed that transitivity scores can stay high after baseline contingencies flip. F et al. give a possible explanation: those scores may ride on reject control, not true class formation.
Why it matters
Before you say a client has formed an equivalence class, check what is controlling the choice. Add a few trials where the negative picture is new. If the learner still picks the old correct one, you have cleaner proof. This quick probe keeps your teaching data honest and saves you from building a program on shaky stimulus control.
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02At a glance
03Original abstract
A detailed analysis is presented of the ways in which control by the negative stimulus in two-comparison conditional discriminations may be expected to affect the outcome of tests for the properties of equivalence relations. Control by the negative stimulus should produce the following results: (a) no observable effect on symmetry tests; (b) reflexivity test results should look like "oddity" rather than "identity"; and (c) transitivity tests that involve an odd number of nodes should yield results that are 100% opposite to tests that involve an even number of nodes. The analysis also considers the effects of variation in the type of comparison-stimulus control between and within baseline conditional discriminations. Methods are suggested for experimentally regulating the type of control, and for verifying the predictions that the analysis generates. If suggested experiments continue to support the analysis, investigators who use two-comparison conditional discriminations to study equivalence relations will either have to control explicitly whether the positive or the negative comparison governs their subjects' choices, or they will have to abandon two comparisons and use three or more comparisons instead.
Journal of the experimental analysis of behavior, 1992 · doi:10.1901/jeab.1992.58-183