Thursday, March 27, 2014

n-gram vs. engram

Engrams are a hypothetical means by which memory traces are stored as biophysical or biochemical changes in the brain (and other neural tissue) in response to external stimuli.

They are also sometimes thought of as a neural network or fragment of memory, sometimes using a hologram analogy to describe its action in light of results showing that memory appears not to be localized in the brain. The existence of engrams is posited by some scientific theories to explain the persistence of memory and how memories are stored in the brain. The existence of neurologically defined engrams is not significantly disputed, though their exact mechanism and location has been a focus of persistent research for many decades.

In the fields of computational linguistics and probability, an n-gram is a contiguous sequence of n items from a given sequence of text or speech. The items in question can be phonemes, syllables, letters, words or base pairs according to the application. n-grams are collected from a text or speech corpus.

An n-gram of size 1 is referred to as a "unigram"; size 2 is a "bigram" (or, less commonly, a "digram"); size 3 is a "trigram". Larger sizes are sometimes referred to by the value of n, e.g., "four-gram", "five-gram", and so on.

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