Six subjects decided whether pairs of adjectives had same or different meanings. Stimuli were 48 first words paired with two synonyms, one antonym, and one unrelated word. Pairs were presented visually, with a delay, interstimulus interval, or ISI, of 0-700 msec between onset of the first word and presentation of the second word. Reaction times, RTs, for "same" and "different" responses were measured from onset of the second word with each of eight delays. The maximum decrease in RT from that with a zero delay was taken as a measure of encoding time, ET, for the first word. This ET was interpreted as the time taken to identify a word and to retrieve from memory meaning information sufficient for successful comparison. The RT X ISI functions obtained were consistent with serial processing. Further support for serial processing was provided by the independence of the effects of first-and second-word length on RT and ET. The average ET was 183 msec, a value in agreement with earlier gross estimates. Words in antonym pairs yielded longer ETs than the same words in synonym or unrelated pairs, apparently reflecting the need for greater information retrieval. The sensitivity of the method as a measurement technique was demonstrated by detection of small but significant effects for word length and frequency.

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