Reflexivity without identity matching training: A first demonstration.

Until now, the equivalence property of reflexivity-matching physically identical stimuli to themselves after training on a set of arbitrary matching relations-has not been demonstrated in any animal, human or nonhuman. Previous reports of reflexivity have either implicitly or explicitly involved reinforced training on other identity matching relations. Here we demonstrate reflexivity without prior identity matching training. Pigeons received concurrent successive matching training on three arbitrary matching tasks: AB (hue-form), BC (form-hue), and AC (hue-hue with different hues in the A and C sets). Afterwards, pigeons were tested for BB (form-form) reflexivity. Consistent with the predictions of Urcuioli's () theory, pigeons preferentially responded to B comparison stimuli that matched the preceding B sample stimuli in testing (i.e., BB reflexivity). A separate experiment showed that a slightly different set of arbitrary matching baseline relations yielded a theoretically predicted "anti-reflexivity" (or emergent oddity) effect in two of five pigeons. Finally, training on just two arbitrary successive matching tasks (AB and BC) did not yield any differential BB responding in testing for five of eight pigeons, with two others showing reflexivity and one showing antireflexivity. These data complement previous findings of symmetry and transitivity (the two other properties of equivalence) in pigeons.