Dugdale, N., & Lowe, C. F. (2000).
Testing for symmetry in the conditional discriminations of language-trained chimpanzees.
Journal of the Experimental Analysis of Behavior,
73, 5-22.
If subjects are taught to match Stimulus A to B and then, without
further training, match B to A, they have passed a test of
symmetry. It has been suggested that nonhumans' lack of success
on symmetry tests might be overcome by giving them a history of
symmetry exemplar training, that is, by directly teaching a large
number of conditional relations (e.g., AB, CD, EF, ...) and also
directly training the "reverse" of these relations
(e.g., BA, DC, FE, . . .). The chimpanzee subjects of the present
study, Sherman, Austin, and Lana, had already received extensive
symmetry exemplar training as a result of attempts to teach a
selection-based language system of lexigrams. The present study
systematically subjected 2 of these chimps (Sherman and Lana),
for the first time, to standard symmetry tests in controlled
conditions. Both chimps failed the tests, even when their correct
responses on test trials were reinforced. The findings do not
support the exemplar training hypothesis, and cast doubt upon
whether the chimps can pass tests of stimulus equivalence.
Key words: symmetry, stimulus equivalence, verbal behavior,
language, conditional discrimination, key press, chimpanzees