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Cognitive and neural correlates of word production

Final Activity Report Summary - WORD PRODUCTION (Cognitive and neural correlates of word production)

We spend most of our time talking, whether it is to ourselves or to others. Speakers can typically find the right word at the right time quickly and easily, despite the large size of their mental lexicons.

Characterising the brain mechanisms that support this remarkable word finding ability is of primary concern for language sciences and represented the primary goal of the present project on word production. Different methods were used in our project, such as neuroimaging techniques, analyses of behavioural responses and testing of patients with language impairment resulting from focal brain lesions. This choice was motivated by the understanding that each method was particularly suited to the investigation of specific aspects of cognitive processing and that a plurality of approaches was needed so as to understand cognitive processing as a whole.

We also used magnetoencephalography (MEG) for one of the studies of our project, which was a technique based on the recording of the magnetic fields generated by brain electrical activity and allowed for measurements of brain activation with excellent temporal resolution and good spatial localisation. A new type of analysis was applied to the MEG recording of the brain activity that was observed when native English speakers named pictures out loud. This analysis allowed for the identification of the brain areas involved in the access to word meaning, the retrieval of word sounds and the articulatory processes determining the proper shaping of the vocal tract. The experiment was completed and data analysis, which required the development of new software, was in progress by the time of the project completion. We expected the data to provide one of the most refined descriptions of the brain regions involved in word naming, their roles in this task and the temporal dynamics of their activation.

Many of the words that speakers produce have a complex structure, being formed by different constituents, i.e. morphemes, as in the case of the words dogs, which consists of dog plus s, or doghouse, being composed by dog and house. How are complex words represented in our brains? What mechanisms enable speakers to produce complex words? Which brain structures support the production of complex words? These questions were addressed in our project by examining compounds, i.e. words like doghouse, which were formed by the combination of two words, in that case dog and house. The response latencies we recorded when English speakers looked passively at compound words indicated that compound words were assembled ‘on the fly’ every time speakers produced them, instead of being stored in memory as whole words. Data converging on this conclusion were obtained from patient RC, who was affected by acquired language impairment as a consequence of brain damage. Patient RC failed to repeat long words such as dinosaur. However, RC’s repetition was flawless when the long words were compounds, as in the case of the words bodyguard and wallpaper. RC’s results could be explained under the hypothesis that compound words were produced by assembling their components. In fact, the problem experienced by RC with a long word such as dinosaur would not affect the shorter words body and guard, if these words were assembled to produce the compound word bodyguard. More generally, the findings that were obtained by our studies on compounds revealed that the language system relied upon compositional processes to produce words with complex structures, even when these words were familiar and had been extensively encountered in the past.