Tests for control by exclusion and negative stimulus relations of arbitrary matching to sample in a "symmetry-emergent" chimpanzee.
Exclusion and S+/S- control can operate together in the same symmetry-ready learner.
01Research in Context
What this study did
A lab chimp that already showed symmetry got new matching-to-sample tests. The trainer used unknown pictures as wrong choices so the ape could only win by picking the new one. This is called exclusion.
Other trials mixed in the usual S+ (correct) and S- (wrong) pictures. The team wanted to see if one chimp could use both tricks at the same time.
What they found
The chimp picked the new picture when the old ones were all wrong. It also kept choosing S+ and avoiding S- when those were shown. Both kinds of stimulus control lived side-by-side.
The animal’s choices followed symmetry-consistent relations, so the same brain that can match can also rule out.
How this fits with other research
Goldman et al. (1979) got goldfish to about 75 % correct with plain matching-to-sample. The chimp went further by also using exclusion, showing a leap in flexible stimulus control.
Mintz et al. (1966) added visual cues inside pigeons’ ratios to cut errors. Gettinger (1993) shows you can instead probe exclusion and S+/S- together to map control without extra cues.
Tracey et al. (1974) saw kids make post-reinforcement errors under fixed schedules. The chimp data say if you test exclusion you may spot true stimulus control hiding behind those error bursts.
Why it matters
If a learner can both pick the known right answer and cross out the impossible one, you have two separate roads to correct responding. Next time a client keeps erring, run a quick exclusion probe: present one brand-new foil with old S- items. A jump to the novel choice tells you the child is using exclusion, not broken stimulus control. Use that path to build stronger equivalence classes and cleaner discrimination.
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02At a glance
03Original abstract
In the present experiments, controlling relations in arbitrary matching-to-sample performance were tested in a 9-year-old female chimpanzee who showed statistically significant emergence of symmetry in previous two-choice conditional discrimination experiments. In Experiment 1, a novel (undefined) sample stimulus was followed by a pair of trained (defined) and undefined comparison stimuli to assess the control by exclusion in arbitrary matching. The chimpanzee selected the undefined shape comparison, excluding the defined one, in color-sample-to-shape-comparison probe trials, although stimulus preferences were relatively stronger than control by exclusion in shape-sample trials. An additional test for control by relations of the sample to the positive comparison (S+ control) showed that her behavior was also under the control of relations of the sample to the positive comparison. In Experiment 2, a defined sample was followed by a pair of negatively defined and undefined comparisons to test control by the relations of the sample to the negative comparison. (S- control). The subject selected undefined comparisons in both color-shape and shape-color test trials. These results clearly indicate that the conditional discrimination behavior of this "symmetry-emergent" chimpanzee was under both S+ and S- control. Furthermore, her performance was also under control by exclusion in color-shape arbitrary matching, unlike other chimpanzees who showed no evidence of symmetry but only S+ control of arbitrary matching.
Journal of the experimental analysis of behavior, 1993 · doi:10.1901/jeab.1993.59-215