Predictability and novelty in literal language comprehension: an ERP study

Linguists have suggested that one mechanism for the creative extension of meaning in language involves mapping, or constructing correspondences between conceptual domains. For example, the sentence, "The clever boys used a cardboard box as a boat," sets up a novel mapping between the concepts cardboard box and boat, while "His main method of transportation is a boat," relies on a more conventional mapping between method of transportation and boat. To examine the electrophysiological signature of this mapping process, electroencephalogram (EEG) was recorded from the scalp as healthy adults read three sorts of sentences: low-cloze (unpredictable) conventional ("His main method of transportation is a boat,"), low-cloze novel mapp'ing ("The clever boys used a cardboard box as a boat,"), and high-cloze (predictable) conventional ("The only way to get around Venice is to navigate the canals in a boat,"). Event-related brain potentials (ERPs) were time-locked to sentence final words. The novel and conventional conditions were matched for cloze probability (a measure of predictability based on the sentence context), lexical association between the sentence frame and the final word (using latent semantic analysis), and other factors known to influence ERPs to language stimuli. The high-cloze conventional control condition was included to compare the effects of mapping conventionality to those of predictability. The N400 component of the ERPs was affected by predictability but not by conventionality. By contrast, a late positivity was affected both by the predictability of sentence final words, being larger for words in low-cloze contexts that made target words difficult to predict, and by novelty, as words in the novel condition elicited a larger positivity 700-900ms than the same words in the (cloze-matched) conventional condition.