Interference theory

Interference theory refers to the idea that forgetting occurs because the recall of certain items interferes with the recall of other items. In nature, the interfering items are said to originate from an overstimulating environment.

In the late 1950s two groups of researchers published very similar methods that demonstrated the interference theory, a husband and wife team, Peterson and Peterson and another researcher, Brown.

In one study done by Peterson and Peterson participants were asked to recall trigrams (string of three letters) at different second intervals, ( 3. 6. 9 etc..) after the presentation of the last letter in the trigram. To make the trigrams impossible to pronounce the investigator used only consonants ( e.g. BWV).. The participants were asked to count backwards to allow no time for rehearsal and for the numbers to interfere with the recall of trigrams. Each of the participants was tested eight times at each of the six delay intervals which totaled to 48 trials. The percentage of recalls decays over time due to interference of the numbers they had to count backwards. From this study Peterson and Peterson concluded that short term memory exists for a few seconds if the participant does not make an active effort to retain the information."

This theory along with the decay theory have been proposed as reasons for why people forget. Evidence for this theory comes from paired associate learning, as well as from Jenkins and Dallenbach's (1924) experiment where they researched forgetting in two students over the period of eight hours.

Types
According to the theory there are three kinds of interference: proactive interference, retroactive interference and output interference.But more emphasis is placed on proactive and retroactive which often happens in our everyday life and dealings.

Proactive interference
Proactive interference occurs when previous learning interferes with new learning. For example, if you knew how to speak French and then tried to learn to speak Spanish, your knowledge of French would hamper your ability to learn Spanish. You might accidentally use French words when attempting to speak in Spanish.

Retroactive interference
Retroactive interference is new learning disrupting your previous learning. Similar to the example above, if you knew French, and then later learned to speak Spanish, your knowledge of Spanish could hamper your ability to remember French. You might recall Spanish words when trying to speak French. The Brown-Peterson task mentioned above is another example of retroactive interference.

Output interference
Output interference occurs when the "activity of retrieving, ITSELF", interferes with the retrieval of the actual information needed in the first place. Primarily, this is caused by the limited capacity of the short-term memory.

however, the above which is proactive and retroactive has been widely been researched and proved to be the main types of interference in psychology.