This is a nice example of the dissociation ofand .
Explicit memory involves the facts you know, the things you know you know, and knowledge you have that you can explicitly articulate. Like knowing what a dog is, knowing who the president is, knowing the capital of the Ottoman Empire in 1888 (Constantinople, not Istanbul), or knowing the ingredients in an aviation cocktail (gin, luxardo, creme de violette, lemon juice).
By contrast, implicit memory is stuff you know that you can't express explicitly. A lot of the earlier examples of implicit memory were motor-related, things like riding a bike or playing guitar. More recently, people have suggested that aspects of language and music are grounded in implicit memory (e.g.,) as well.
There is a lot of evidence that there are two different systems, neurally and cognitively. Neurally, explicit memory is generally associated with the; implicit memory is associated with the . Aside from copious brain-imaging evidence, there is also evidence for degenerative diseases: Alzheimer's primarily starts in the ventricles by the hippocampus and is well known to greatly impact people's memories: what they've done and who people are. In contrast, Alzheimer's patients do a remarkable job of remembering songs (implicit memory) and skills, like riding a bike. In contrast, Parkinson's patients lose their motor abilities, especially complicated skills. In contrast, they are otherwise very sharp, in terms of maintaining memories of their lives and knowledge. Parkinson's is a disease of the basal ganglia. (See the above linked paper for references).
Cognitively there's a nice little study that demonstrates the difference between the two memory systems. Thetest is sort of like a game of Guitar Hero (e.g., ) - you have to mirror or follow sequences of key presses, positions on a screen or something similar. To the person doing the experiment, the sequences are random, and indeed most of it is. But here's the secret: embedded within are repeated sequences appearing over and over.
So, you get faster when you're repeating sequences you've already done before without any actual knowledge of what is really going on. Indeed, after the test, participants have no recollection of what the repeated sequences were or even learning anything at all. Implicit memory magic!
Typing is a near-perfect example of implicit memory.
Of course, the two interact—you can explicitly examine what is involved in any implicit activity and with typing, many have. A big area of research is understanding how to get the two to interact to improve learning ( ). But the key is that you don't need any explicit knowledge to be able to successfully learn things that are implicitly learnable.
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