Letter constraints within words in printed English

Summary

Due to the manner in which the English language is used, words exhibit strong internal constraints on letters, but some additional constraint may be imposed by the context in which words appear. In order to estimate the internal constraints of words and the overall effect of context, an experiment was carried out using 225 human subjects who predicted letters in each of the first four positions within words, both with and without context prior to the words. It was found that as more letters at the beginning of words are given, prediction of the following letters increases monotonically, but the increase is not smooth. Prediction of the third letter of words given the first two letters is only a little better than prediction of the second letter given only the first. This effect may be explained by the probable combinations of vowels and consonants at the beginning of words. Letters in the first two positions show no improvement due to long context but prediction of later letters is increased by such context so that prediction rises smoothly from the initial letter to the fourth letter. Also, the type of word in which the letters are to be predicted affects the prediction, function words showing more constraint on letters than content words. The difference between function and content words does not take effect, however, until the first two letters of the word are given. Using the prediction data from words preceded by long context, extrapolations of constraint out to the tenth letter were obtained. From the values of constraint at the first ten letter positions it was possible to estimate the maximum unilateral sequential constraint in English. A value of about 48% was obtained which compares with previous estimates of 50%. A further evaluation of the overall effect of context indicates that about 81% of the constraint in English is contained within the words themselves, and the other 19% is due to any additional context.