p547fig15.15 Expected non-occurences do not prevent the processing of sensory events and their expectations.  Rather, they prevent mismatches of those expectations from triggering orienting reactions.<BR>||  Expected non-occurrence of goal.  Some rewards are reliable but delayed in time.  Does <I>not</i> lead to orienting reactions: <I>How?</i>  Both expected and unexpected nonoccurrences are diue to mismatch of a sensory event with learned expectations.   Expected non-occurrences do not inhibit sensory matching: eg a pigeon can see an earlier-than-usual food pellet.  Hypothesis: Expected non-occurrences inhibit the process whereby sensory mismatch activates orienting reactions.   Mismatch not-> orient.