Long-term Memory

Any material that survives the tight capacity and duration limits of short-term memory finally enters long-term memory (LTM), which functions as a vast, essentially permanent storehouse. It can hold information as recent as what a person ate for breakfast yesterday and as distant as memories from early childhood. A striking claim associated with LTM is that once information genuinely enters this store, it is never truly lost — because it gets encoded semantically, that is, in terms of the meaning the information carries, rather than in terms of surface features. On this view, what we experience as 'forgetting' from long-term memory is really retrieval failure: for one reason or another, we simply cannot access information that is, in fact, still stored.

How does information actually travel from one store to the next, and what keeps it in a given store once it is there? Atkinson and Shiffrin answered this with the idea of control processes — active mechanisms that regulate the flow of information between the three memory systems. The first control process is selective attention, which decides which sensory impressions get passed on from the sensory registers into STM; anything not attended to fades away almost immediately. Within STM, a second control process, maintenance rehearsal, keeps information available for as long as it is needed simply through repetition — silently or aloud repeating the material — but as soon as the repetition stops, the information is lost. A third control process, chunking, works to expand the otherwise very limited capacity of STM (roughly seven items, plus or minus two) by combining several smaller units into fewer, larger, meaningful units. For instance, a long string of digits that exceeds STM's normal capacity can be broken into meaningful chunks — such as grouping digits into recognisable years — making the whole string far easier to hold onto. Finally, information moves from STM into the permanence of LTM through elaborative rehearsal, a very different process from maintenance rehearsal: instead of just repeating information, elaborative rehearsal connects the new material to information that already exists in long-term memory, building associations with concepts, meanings, and life experience. The more such associations a person builds around new information, the more likely that information is to become a lasting part of long-term memory. …