Proactive Interference - Keppel and Underwood (1962)

Proactive interference occurs when old information stored in long-term memory, interferes with the learning of new information.

This usually occurs when the new information is similar to the old information. An everyday example of proactive interference is when you get a new mobile phone number, as your memory for your old number disrupts your attempts to remember your new number.

Keppel and Underwood (1962) examined the effect of proactive interference on long-term memory, in an experiment that resembles Peterson and Peterson (1959).

Participants were presented with meaningless three-letter consonant trigrams (for example, THG) at different intervals (3, 6, 9 second, etc). To prevent rehearsal the participants had to count backwards in threes before recalling.

Keppel and Underwood found that participants typically remembered the trigrams that were presented first, irrespective of the interval length.

They concluded that the results suggest proactive interference occurred, as memory for the earlier consonants, which had transferred to long-term memory, was interfering with the memory for new consonants, due to the similarity of the information presented.