The blocking effect, canonical in the study of associative
learning, is often explained as a failure of the blocked cue to
become associated with the outcome. However, this
perspective fails to explain recent findings that suggest
learning about a blocked cue is superior to a different type of
redundant cue. We report an experiment designed to test the
proposal that blocking is not a failure of association, but a
performance effect arising from a comparator process
(Denniston, Savastano, & Miller, 2001). Participants received
A+ AX+ BY+ CY- training containing a blocked cue X and
another redundant cue Y, before rating outcome expectancies
for individual cues. These ratings were inconsistent with the
association-failure view. After subsequent A- Y+ training,
participants rated cues again. Ratings in the second test were
inconsistent with the comparator theory. Our data suggest that
neither perspective is likely to provide a complete account of
causal learning
