proactive interference. The subjects who read additional passages, whether
presented before or after the critical passage, recalled less about the critical
passage than subjects who read only the critical passage. The more additional
passages the subjects read, the poorer was their recall of the critical passage.
Another way in which interference is demonstrated is in experiments that
measure how fast people can decide whether a fact about a concept was on a
previously memorized list of facts. Interference in this paradigm takes the form
of an increased response latency to facts whose concepts are found in lots of
other facts on the list. In one such experiment, subjects memorized sentences
that described a professional in some location (e.g., ‘‘The lawyer was in the
park’’ ). The number of facts about any one professional or about any one loca-
tion varied. Subjects might memorize two facts about a lawyer (e.g., ‘‘The law-
yer was in the park,’’ ‘‘The lawyer was at the beach’’ ) and one fact about a
doctor (e.g., ‘‘The doctor was in the park’’) and might memorize two facts that
involved parks and one fact that involved beaches. The typical result (illus-
trated in figure 14.6 for ‘‘true’’ responses) is that the more facts associated with
a character or with a location, the longer it takes to decide if the fact is true or
false (Anderson, 1974, 1976). Sometimes this finding is known as thefan effect.
The more facts that ‘‘fan off ’’ a concept, the longer it takes to verify whether any
given fact about the concept was previously memorized.
Explaining Interference
The record-keeping theory has an easy explanation for interference. People
search memory records by first finding in memory a target element, such as
a character’s profession. People then scan through the set of facts associated
with the target element until the desired fact is found, or until the search is
exhausted. The more associations to be searched, or the longer or more effort it
takes to find the desired fact, the more likely the fact will not be found. It is as if
Figure 14.6
The more facts about a professional or location, the longer the response time to verify the fact.
Based on Anderson, 1974.
346 R. Kim Guenther