VALUE TRANSFER IN CONCURRENT-SCHEDULE DISCRIMINATIONS BY PIGEONS

When pigeons are trained on a discrete-trial simultaneous discriminati on, some of the value associated with the positive stimulus appears to transfer to the negative stimulus (Zentall & Sherburne, 1994). Pigeon s preferred a negative stimulus that had been discriminated from an al ways-positive stimulus (S+) over a negative stimulus that had been dis criminated from a sometimes-positive stimulus (S+/-). A very different finding (suggestive of transitivity of preference or contrast) was re ported by Belke (1992). On concurrent probe tests of stimuli associate d with equal variable interval (VI) schedules but originally trained i n alternative concurrent pairs (one with a richer schedule, the other with a poorer schedule-VI 20 sec vs. VI 40 sec and VI 40 sec vs. VI 80 sec), the stimulus originally paired with the poorer schedule was pre ferred. But Belke's results may have been obtained because the pigeons had been trained to peck the VI 40 sec paired with the poorer schedul e and they had been trained not to peck the VI 40 sec paired with the richer schedule. In the present experiment, we avoided this bias by tr aining pigeons on two concurrent schedules in which the tested stimuli both had been associated with the poorer schedule of the pair [A(VI 2 0 sec) vs. B(VI 80 sec) and C(VI 40 sec) vs. D(VI 80 sec)]. Evidence f or value transfer was demonstrated when on probe trials pigeons prefer red B over D.