Found:

Oddity discrimination

PHONETICS: In this three-stimulus task the subject is presented with a ‘triangle’ (ABC) of stimuli, two of which are alike, and is asked to locate the ‘odd’ one. This may be any of the three. There are six possible stimulus sequences: (S1, S2, S2) and (S2, S1, S1), for both of which the correct response is ‘A’; (S2, S1, S2) and (S1, S2, S1), for which the answer is ‘B’; (S1, S1, S2) and (S2, S2, S1), for which the answer is ‘C’.

LIT.	Macmillan, N.A., & Creelman, C.D. (1991)