Control by sample location in pigeons' matching to sample.
Sample location can steal stimulus control and stop symmetry before it starts.
01Research in Context
What this study did
Researchers taught pigeons a three-key matching-to-sample task.
The sample picture could appear on the center key or on one of the side keys.
They wanted to see if birds would still pick the correct comparison no matter where the sample showed up.
What they found
Accuracy crashed when the sample moved to a side key.
Even after extra training with mixed locations, birds kept making below-chance errors.
The birds were not looking at the picture; they were pecking the place.
How this fits with other research
Two years later the same lab fixed the problem. Mueller et al. (2000) trained pigeons with the sample popping up in many spots from the start.
Those birds transferred perfect matching to brand-new locations, proving control by the picture, not the place.
Lionello-DeNolf (2021) review counts this 1998 study as a classic case where location control blocks symmetry in nonhumans.
Perez et al. (2020) saw a similar crash when they blocked the view of the correct comparison—both tweaks show that tiny layout choices can hijack stimulus control.
Why it matters
For your learners, rotate where the sample sits every few trials.
If you always park the SD on the left, you may be teaching "left-side" responding instead of the actual concept.
Check by shifting the card to a new spot and probe without prompting.
If accuracy drops, you just caught location control early and can retrain before it blocks equivalence.
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02At a glance
03Original abstract
Three experiments assessed the impact of sample location in pigeons' matching to sample. Experiments 1 and 2 demonstrated that after line or hue identity matching was acquired to high levels of accuracy with center-key samples, varying sample location across the three keys disrupted performances. The drop in accuracy occurred following both zero-delay and simultaneous training and was mostly confined to trials in which the sample appeared on a side key. Experiment 3 attempted to diminish control by location by training birds to match samples that could appear in any location prior to center-key sample training and moving-sample testing with another set of stimuli. In testing, all birds performed accurately on center-sample trials and on side-key sample trials in which the matching choice appeared on the center key. Accuracy was below chance, however, on side-key sample trials in which the matching choice appeared on the other side key. One implication of the persistent control by sample location in the three-key paradigm is that it precludes the possibility of symmetry because symmetry tests require a change in the locations at which samples and comparisons appear.
Journal of the experimental analysis of behavior, 1998 · doi:10.1901/jeab.1998.70-235