Symmetry and stimulus class formation in humans: Control by temporal location in a successive matching task
Humans form symmetry relations in matching-to-sample no matter when the sample appears, so equivalence lessons don't need rigid timing.
01Research in Context
What this study did
Beurms et al. (2017) asked adults to do a matching-to-sample task on a computer. The sample picture stayed on, then two choice pictures appeared later. The trick was timing: the team slid the sample to an earlier or later spot in the trial. They wanted to see if the new timing stopped people from forming symmetry relations (A=B then B=A).
What they found
People still passed symmetry tests even when the sample popped up at odd moments. Changing the sample's time slot did change response speed, but the equivalence classes held firm. In short, humans don't need fixed timing to derive 'same-as' relations.
How this fits with other research
Greene et al. (1978) showed that humans need a visible clock to produce the smooth 'scallop' on fixed-interval schedules. Beurms removes the clock and still gets orderly stimulus relations. The two studies together say: timing cues matter for schedule pausing, yet not for equivalence.
Taylor et al. (1993) taught adults equivalence with negative-comparison control; Beurms keeps the same matching format but swaps in temporal-location control. Both report strong emergent relations, proving the procedure is robust across different controlling variables.
Webb et al. (1999) found that pigeons' matching accuracy flips when sample duration is unpredictable. Beurms sees no such flip in humans; symmetry survives unpredictable timing. The species comparison hints that people encode temporal order differently than birds, not that one species is 'better'.
Why it matters
You can relax about clock-like precision when you run equivalence lessons with verbal clients. Slide stimuli around, insert pauses, or let the learner set the pace—symmetry will still emerge. Save the tight timing for schedule-based fluency drills; for equivalence, focus on the relations, not the clock.
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02At a glance
03Original abstract
Symmetry refers to the observation that subjects will derive B-A (e.g., in the presence of B, select A) after being trained on A-B (e.g., in the presence of A, select B). Whereas symmetry is readily shown in humans, it has been difficult to demonstrate in nonhuman animals. This difficulty, at least in pigeons, may result from responding to specific stimulus properties that change when sample and comparison stimuli switch roles between training and testing. In three experiments with humans, we investigated to what extent human responding is influenced by the temporal location of stimuli using a successive matching-to-sample procedure. Our results indicate that temporal location does not spontaneously control responding in humans, although it does in pigeons. Therefore, the number of functional stimuli that humans respond to in this procedure may be half of the number of functional stimuli that the pigeons respond to. In a fourth experiment, we tested this assumption by doubling the number of functional stimuli controlling responding in human participants in an attempt to make the test more comparable to symmetry tests with pigeons. Here, we found that humans responded according to indirect class formation in the same manner as pigeons do. In sum, our results indicate that functional symmetry is readily observed in humans, even in cases where the temporal features of the stimuli prevent functional symmetry in pigeons. We argue that this difference in behavior between the two species does not necessarily reflect a difference in capacity to show functional symmetry between both species, but could also reflect a difference in the functional stimuli each species responds to.
Journal of the Experimental Analysis of Behavior, 2017 · doi:10.1002/jeab.282