Decoding the dictionary: Study suggests lexicon evolved to fit in the brain

Troy, N.Y. – The latest edition of the Oxford English Dictionary boasts 22,000 pages of definitions. While that may seem far from succinct, new research suggests the reference manual is meticulously organized to be as concise as possible — a format that mirrors the way our brains make sense of and categorize the countless words in our vast vocabulary.

“Dictionaries have often been thought of as a frustratingly tangled web of words where the definition of word A refers users to word B, which is defined using word C, which ends up referring users back to word A,” said Mark Changizi, assistant professor of cognitive science at Rensselaer Polytechnic Institute. “But this research suggests that all words are grounded in a small set of atomic words — and it’s likely that the dictionary’s large-scale organization has been driven over time by the way humans mentally systematize words and their meanings.”

Dictionaries are built like an inverted pyramid. The most complex words (e.g., “albacore” and “antelope”) sit at the top and are defined by words that are more basic, and thus lower on the pyramid. Eventually all words are linked to a small number of words — called “atomic words,” (such as “act” and “group”) — that are so fundamental they cannot be defined by simpler terms. The number of levels of definition it takes to get from a word to an atomic word is called the “hierarchical level” of the word.

Changizi’s research, which was published online this week and will appear in the June print edition of the Journal of Cognitive Systems Research, indicates that the dictionaries we use every day utilize approximately the optimal number of hierarchical levels — and provide a visual roadmap of how the lexicon itself has culturally evolved over tens of thousands of years to help lower the overall “brain space” required to encode it, according to Changizi.

Many other human inventions — such as writing and other human visual signs — have been designed either explicitly or via cultural selection over time so as to minimize their demands on the brain, Changizi said.

By conducting a series of calculations based on the estimation that the most complex words in the dictionary total around 100,000 different terms, and that the number of atomic words range from 10 to 60, Changizi was able to devise three signature features present in the most efficient dictionaries — as well as in their human counterpart, the brain.