Symmetry in the pigeon with sample and comparison stimuli in different locations. II.
Keep stimulus locations identical across training and equivalence probes or you risk losing emergent relations.
01Research in Context
What this study did
The team worked with pigeons in a lab. They first taught each bird to peck the correct key when colors appeared in fixed spots.
Next they tested symmetry: if red-on-left means green-on-right, will the bird now pick red when green is on the right?
Crucially, they ran these probe trials twice—once with colors in the original places, once with the same colors shifted to new screen spots.
What they found
Symmetry showed up only when the colors stayed in their trained locations. Move a color two inches left and the relation vanished for most birds.
The birds acted as if “where” was part of “what” they had learned.
How this fits with other research
Saunders et al. (1988) saw no symmetry at all in pigeons. The new study says symmetry can emerge, but it is glued to place.
Haemmerlie (1983) found pigeons easily transfer matching to brand-new key spots. Melissa et al. now show the opposite: symmetry breaks when spots change. The tasks differ—memory for place versus emergent relations—so the clash is only skin-deep.
Ribes-Iñesta (1999) strengthened equivalence by reinforcing special observing responses. Together the papers warn us: in pigeons, tiny shifts in space or reinforcement can wipe out or build stimulus classes.
Why it matters
For BCBAs the lesson is clear: keep the physical layout of stimuli identical across training and test sessions. If you move pictures, words, or icons to a new corner of the screen or table, you may lose the untaught relations you worked hard to create. Check location before you blame the learner for “not generalizing.”
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02At a glance
03Original abstract
Pigeons were trained on arbitrary (hue-form) and identity (hue-hue and form-form) successive matching with center-key samples and left-key comparisons. Later, they were tested on form-hue (symmetry) probe trials that were structured either in the different-locations fashion as the baseline trials (viz., center-key samples and left-key comparisons) or with a constant location by using center-key samples and center-key comparisons. Three of four pigeons showed symmetry when the probe-trial samples and comparisons appeared in center- and left-key spatial locations, respectively, but none did when both appeared in one (center-key) location. Subsequently, pigeons previously tested with center-key samples and left-key comparisons were tested with those form-hue stimuli shown in the same (center-key) location, and vice versa for the other pigeons. None of the former pigeons showed symmetry on the second test even if they had on the first test. By contrast, two of three pigeons that had not shown symmetry with single-location samples and comparisons did so when those stimuli appeared in different (center- vs. left-key) locations. Taken together, these results show that symmetrical relations between the same, nominal matching stimuli depend on where those stimuli appear in testing vis-à-vis in training and, more generally, confirm that spatial location is part of the functional matching stimuli.
Journal of the experimental analysis of behavior, 2015 · doi:10.1002/jeab.162