Interference is when two pieces of informationdisrupt each other
Forgetting occurs in LTM because we can't get access to memories even though they are available
Types of interference
Proactiveinterference (PI)
PI occurs when oldermemory disrupts a newer one
For example, a teacher learns manynames in the past and can'tremembernames of her currentclass
Retroactiveinterference (RI)
RI happens when a newermemory disrupts an older one
For example, a teacher learns many newnames this year and can'tremember the names of her previousstudents
Interference is worse when memories are similar
This may be because:
In proactive interference previouslystoredinformation makes newinformation more difficult to store
In retroactive interference, newinformationoverwritespreviousmemories which are similar
McGeoch and McDonald (1931) Effects of similarity: Procedure
Ppts were asked to learn a list of words to 100%accuracy (recall perfectly)
Then they were given a newlist to learn. The newmaterial varied in the degree to which it was similar to the old:
Group 1: synonyms - words had samemeanings as the originals
Group 2: antonyms - words had oppositemeanings to originals
Group 3: unrelated - words unrelated to the original ones
Group 4: consonant syllables
Group 5: three-digit numbers
Group 6: no new list - ppts just rested (controlcondition)
McGeoch and McDonald (1931) Effects of similarity: Findings and Conclusion
Performance depended on the nature of the second list. The most similarmaterial (synonyms) produced the worstrecall
This shows that interference is strongest when the memories are similar
One strength is some support for interference in real-worldsituations
Baddley and Hitch (1977) asked rugbyplayers to recall the names of teams they had playedagainst during a rugbyseason
Players did not play the same number of games (injuries). Those who playedmost (more interference) had poorestrecall
This shows that interference operates in some everydaysituations, increasing the validity of the theory
Counterpoint for support for interference in real-world situations:
Interference in everydaysituations is unsual because the necessaryconditions are relativelyrare e.g. similarity of memories/learning does not occuroften
Therefore most everydayforgetting may be betterexplained by other theories (e.g. retrievalfailure due to lack of cues)
One limitation is that interferenceeffects may be overcome using cues
Tulving and Psotka (1971) gave ppts lists of wordsorganized into categories (not toldwhat they were)
Recall of firstlist was 70% but fell with each newlist (proactive interference). When given a cuedrecall test (names of categories) recall rose again to 70%
This shows that interference causes just a temporaryloss of access to material still in LTM - notpredicted by theory
Another strength is support from drug studies
Materiallearnedjustbefore taking diazepamrecalledbetter than a placebo group oneweek later - this is retrogradefacilitation (Coenen and Van Luijtelaar 1997)
The drug stoppednewinformation reaching brainareas that processmemories, so it could notretroactivelyinterfere with storedinformation (Wixted)
This shows that the forgetting is due to interference - reducing the interferencereduced the forgetting
Evaluation extra: Validity issues
Lab studies of interference have tightcontrol of confoundingvariables (e.g. time), thus clear link between interference and forgetting
However, most research is unlikeeverydayforgetting. In everydaylife we often learnsomething and recall it muchlater (e.g. revising for exams)
This means that because research is mostly lab-based it may overestimate the importance of interference as a cause of forgetting