What a lot of different memory types there are in the literature! This is made more confusing because so little is known about memory. So we have: sensory, working, short-term, long-term, explicit, implicit, declarative, procedural, semantic, episodic without mentioning obscure types like flashbulb memories. It is also not always clear where authors believe things are happening: amygdala, cerebellum, various parts of the cerebral cortex, hippocampus. Divisions seems to be made on the basis of: what is being stored, how it is being stored, how long it is stable, how large the store, where the store, how it is recalled, what it is used for, and whether it appears consciously.
When I think about it there seems much less division between types when they meld into one another. For example the phrase short-term memory sometimes seems to mean working memory and at other times seems to mean a memory that is identical to a long-term memory except that it has not gone through a final chemical ‘fixing’ operation. Sometime implicit is used for a type of learning that is never conscious – the information gathering and its processing is not conscious and neither is its retrieval and use. At other times the process of consciously practicing some skill until it is performed unconsciously is called implicit. But in this case the memory was transformed from explicit to implicit. It seems to me that semantic memories start out as episodic ones. One day when I was fairly young I had an episodic memory of a particular teacher on a particular day teaching the 7 times table. That memory is long gone as was the other memories of my early use of 7 in multiplication, but these disappeared memories were the source of some semantic memory of the arithmetic facts. And although procedural memories are so often unconscious, many (but not all) can be made conscious serial routines quite easily by just mentally ‘walking’ through them. It seems reasonable to assume that there are actually very few physical types of memory and the apparent differences are due to how/why the physically memory is formed and how/why it is used. It may be that there are actually only a very few memory stores and perhaps only one mechanism of storage (strengthened synapses).
In the literature, there is a background of attempts to force biological memory into a computer model. There is mention of encoding, indexing, bits of information in memory, registers, RAM. Although the words are useful at times, they do beg the question of exactly what is really happening.
A recent paper puts an interesting notion in the mix. Beaudry et al treat ‘focus of attention’ as a form of memory. This seemed unusual at first but then made great sense. Attention is sometimes considered on its own, or as part of working memory, or as part of consciousness. Something is connected in these three entities. What if the content being stored and accessed is physically the same but the ‘when’ and ‘why’ is different? What if there is no big difference between consciousness and memory? Just because memory is something very particular and separate in the computer, there is no reason, per se, why it needs to be separate from perception, cognition or consciousness in the brain. So I am quite grateful that this paper started me thinking along these lines.
According to some current theories, the focus of attention (FOA), part of working memory, represents items in a privileged state that is more accessible than items stored in other memory systems. One line of evidence supporting the distinction between the FOA and other memory systems is the finding that items in the FOA are immune to proactive interference (when something learned earlier impairs the ability to remember something learned more recently). The FOA, then, is held to be unique: it is the only memory system that is not susceptible to proactive interference. We review the literature used to support this claim, and although there are many studies in which proactive interference was not observed, we found more studies in which it was observed. We conclude that the FOA is not immune to proactive interference: items in the FOA are susceptible to proactive interference just like items in every other memory system. And, just as in all other memory systems, it is how the items are represented and processed that plays a critical role in determining whether proactive interference will be observed.
O. Beaudry, I. Neath, A.M. Surprenant, & G. Tahan (2014). The focus of attention is similar to other memory systems rather than uniquely different. frontiers in Human Neuroscience, 8 : doi:10.3389/fnhum.014.00056