Neural basis of the Word Frequency Effect and Its Relation to Lexical Processing

A number of experimental results have shown that in terms of cognitive processing common words – words that occur frequently differ from uncommon words. People perceive common words more accurately and more quickly when listening (Savin, 1963) and also name them more quickly (Oldfield and Wingfield, 1965) while speaking. Also, people produce the common words in more reduced and shortened forms than uncommon words (Whalen, 1991; Gahl, 2008). These results indicate a certain processing difference between the common (or frequent) words and the uncommon (or infrequent) words. This phenomenon has been extensively studied in the psycholinguistic literature, in particular for speech production, as one way of probing the cognitive architecture. Current models in single word production generally agree that the production process consists of multiple cognitive actions (Dell, 1986; Levelt et al. 1999). Broadly speaking, they include conceptulization, retrieval of syntactic and semantic information from the mental lexicon, retrieval of phonological form, assembly of sounds into syllables (syllabification), and finally implementation of speech motor plan in terms of commands to specific muscles to execute the articulation. It is possible that any one, or all, of these activities could be affected by word frequency. Indeed several studies have pointed to an effect of word frequency at different stages of speech production (see e.g. the contrasting accounts of Jescheniak & Levelt, 1994; Gahl, 2008, details on Section 2). However, studies seeking neural evidence of the processing difference by word frequency have so far yielded inconsistent results that cannot be uniformly accounted for. The present study aims to fill this gap by finding a more reliable neural basis of the effect of word frequency using high density intracranial recordings during word reading. In addition, this study analyzes both oneand two-syllable words in order to observe a possible processing difference caused by the number of syllables. Since several studies suggest that word frequency affects processing of words differently depending on the number of syllables (Balota& Chumbley, 1985; Jescheniak& Levelt, 1994), it might be relevant to