An MEG study of picture naming

The purpose of this study was to relate a psycholinguistic processing model of picture naming to the dynamics of cortical activation during picture na ming. The activation was recorded from eight Dutch subjects with a whole-he ad neuromagnetometer. The processing model, based on extensive naming laten cy studies, is a stage model. In preparing a picture's name, the speaker pe rforms a chain of specific operations. They are, in this order, computing t he visual percept, activating an appropriate lexical concept, selecting the target word from the mental lexicon, phonological encoding, phonetic encod ing, and initiation of articulation. The time windows for each of these ope rations are reasonably well known and could be related to the peak activity of dipole sources in the individual magnetic response patterns. The analys es showed a clear progression over these time windows from early occipital activation, via parietal and temporal to frontal activation. The major spec ific findings were that (1) a region in the left posterior temporal lobe, a greeing with the location of Wernicke's area, showed prominent activation s tarting about 200 msec after picture onset and peaking at about 350 msec, ( i.e., within the stage of phonological encoding), and (2) a consistent acti vation was found in the right parietal cortex, peaking at about 230 msec af ter picture onset, thus preceding and partly overlapping with the left temp oral response. An interpretation in terms of the management of visual atten tion is proposed.