Most associative theories have assumed that stimulus competition occur
s only between conditioned stimuli (CSs) that are trained in compound.
The present research investigated the possibility of competition betw
een two CSs that were individually paired to the same unconditioned st
imulus (US). We used human subjects in an anticipatory suppression ana
logue to Pavlovian conditioning. Experiment 1 showed that X+ training
followed by A+ training resulted in impaired responding to X. This did
not occur when hf training preceded X+ training. Experiment 2 replica
ted the basic effect and showed that it did not occur when the Phase 2
training consisted of A- instead of A+ nor when the A+ pairings occur
red in a second context. Experiment 3 showed that A+ pairings occurrin
g in a second context could still produce the effect when X was tested
in the context in which the Af pairings had occurred, but not when X
was tested in a context different from that used for A+ training. Coll
ectively, these results suggest that individually trained CSs may comp
ete with each other when one of those CSs is more strongly activated b
y the test context than the other one.