Estimation of mental lexicon size with word familiarity database

A familiarity database was developed for about 80,000 Japanese words of which familiarity scores were rated by 32 Japanese adults using a 7-point scale in auditory, visual, and audio-visual modalities. Auditory, visual, and audio-visual stimulus words were selected from the database according to their word familiarity for size estimation of the mental lexicon. Sixty Japanese adults participated in a two-alternative forcedchoice task (Know–Don't know) for the stimulus words. The size of the mental lexicon was estimated as the number of words of which familiarity is above a particular word corresponding to 50% point on the fitted logistic curve to “know”-response probability of the stimulus words. The estimated size was about 68,000 for auditory words, and about 66,000 both for visual and audio-visual words when homophones and homographs were included. The results suggest that very small difference in the mental lexicon size among modalities.