Interference (learning)

Interference theory (also known as retrieval interference (Roediger & Karpicke, 2006)) refers to the idea that forgetting occurs because the recall of certain items interferes with the recall of other items. Generally speaking the interference causes slower learning and porer memory

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 time intervals 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 were 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. More emphasis, however, is placed on proactive and retroactive which often happens in our everyday life and dealings.

Proactive interference
Underwood (1957) provided early evidence that things you've learned before encoding a target item can worsen recall of that target item. In a meta-analysis of multiple experiments, he showed that the more lists one had already learned, the more trouble one had in recalling the most recent one. This is proactive interference, where the prior existence of old memories makes it harder to recall newer memories.

Proactive interference can be potently demonstrated with the Brown-Peterson paradigm (Brown, 1958; Peterson & Peterson, 1958). A single Brown-Peterson trial consists of a study list, a retention interval and then a recall period. The study list might consist of a handful of related items (such as a handful of animals or occupations), presented individually every few seconds. For the duration of a short retention interval, subjects are then asked to perform an engaging distractor task such as counting backwards in sevens (to minimize rehearsal). Finally, subjects are asked to recall the items from this study list.

Usually, subjects' back side recollection is nearly perfect for the first trial, but perform increasingly poorly on subsequent trials that use study lists drawn from the same category. This is the proactive interference effect described earlier. In other words, even though the lists from previous trials are now irrelevant, the fact that they were studied at all is somehow making it harder for subjects to recall the most recent list.

Retroactive interference
Retroactive interference occurs when later learning interferes with previous learning; i.e., learning new things somehow overwrites or obscures existing knowledge.

Output interference
Output interference occurs when the act of retrieving 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.