A venerable theory of forgetting, the largest part of which was generated in the great dustbowl of empirical psychology, circa 1940s by researchers such as Benton J. Underwood. The two pivotal concepts invoked to explain forgetting are retroactive interference, and proactive interference. The term inhibition is also used in place of interference. Perusing the literature, you will likely come upon much use of the word paradigm, and such things as the AB-AC design. The founders of interference theory were unashamedly mechanistic in their approach to human memory, which did lead to some nicely established statistics regarding forgetting effects, but which also led to a tangled web of continually disputed and refined accepted research paradigms and findings.

I'll present the vastly simplified crux of the matter, because trust me explicitly when I say this, you do not want to know the minutae. Insanity is just a paradigm away.

retroactive interference:

        
 Learn A (-------elapsed time------) Recall A
        
 Learn A Learn B (---elapsed time--) Recall A

Take a list of words A (the above diagram). Learn the words to one perfect recitation. Now allow an hour to lapse, and attempt to remember all the words A(in no particular order). You will find that you forget some of them (on average), and that's normal because we forget things. If you had learned *another* list of words B during the retention period of the initial list, and then proceeded blithely with your attempt to recall the first list A as per usual, you would find that the number of words recalled would be on average lower! The second list B was providing a retroactive interference effect and causing an increase in forgetting; 'that coming after - interfering with that which came before'.

This was for some time presumed to be the strong form of interference, due predominantly to the type of tasks that researchers used ; paired-associate tasks with relatively short retention intervals.

proactive interference:

         
 Learn A (-------elapsed time------) Recall A
         
 Learn A Learn B (---elapsed time--) Recall B

Ok, grab tight hold of a list of words A again, and learn those suckers. Do the crazy recall A thing as we established earlier. Did you expect not to forget some again? Now, if you had learned an additional list B soon after the first list A , and then after an hour or so tried to recall *only* this second additional list B, your recall would have been poorer. The first list A was providing a proactive interference effect, and increasing forgetting for the second list B. 'that coming before - interfering with that which came after'.

Although this type of interference was originally presumed to be the sickly younger sibling of retroactive, Underwood later established that it is far more likely to have an effect on forgetting in our everyday lives. After all, there is generally a lot more that you have learned before, than within, any retention interval. With enough interfering lists, this type of interference causes catastrophic forgetting.

Does this all mean anything?

As applied to actual life, most effects studied in the context of a tightly controlled experimental setting just get washed out in the noise of complexity. However, it is likely that interference effects will play a part in your day to day forgetting. If you are trying to not forget things (ie school, university, work) that you have learned over a relatively brief period, cramming in other words, you may be able to reduce these effects.

Most mnemonics rely upon elaborative association of the things to be remembered. This is an example of providing cues for retrieval, and very explicit ones at that. However, just about everything you experience is a cue for retrieval from episodic memory (the memory tied to times/events basically). The desk at which you study, the music which you are listening to, the time of day at which you learned something, your mood, are all potential cues.

Interference effects are lessened if you can reduce the sharing of cues by seperate lists/subjects/ things to remember. The distinctiveness of cues is enhanced when they refer to fewer distinct things to be remembered. So, try to split your learning episodes up into seperate 'learning spaces'. Studying everything at once, particularly if the things studied share enough similarity to be confused with one another, can increase interference effects. You may remember the wrong thing, or your recall in general may be lowered by a failure to discriminate between competing responses. If you can give yourself some distinctive cues regarding *when* you learned something, or *what* you were doing, your recall may be improved.

No hard and fast rules here, and in the case of semantic memory, when you can't actually remember when you learned a thing (try remembering when you learned the word "plant"), we are in a very different section of the story. Research is still struggling with the semantic versus episodic thing.

"everything suffers from retroactive interference effects"

the reader's exercise is to explain why this is true or false.

"everything suffers from proactive interference effects"

the reader's exercise is to explain why this is true or false.