Neural Correlations of Processing Lexically and Grammatically Degraded Linguistic Stimuli in a Familiar Narrative Context

Abstract

Functional activation for language processing in left hemisphere language regions has been shown to be correlated with intelligibility of the speech signal, with more intelligible stimuli yielding greater activation. We created stimuli in which intelligibility was reduced in two distinct ways. First, we created lexically degraded stimuli in which lexical items were spectrally rotated. Second, we created grammatically degraded stimuli in which function words and morphemes were spectrally rotated and scrambled in order. We hypothesized that contrasting these conditions would reveal brain areas differentially involved in processing lexical or grammatical information when matched for intelligibility. We used functional MRI to investigate differences in the neural response to normal and degraded stimuli. Stimuli were presented such that normal segments alternated with degraded ones in the context of a familiar narrative. Our results showed no statistically significant differences in activation between lexically and grammatically degraded stimuli. Surprisingly, we also found only a small difference in the anterior middle temporal gyrus between either kind of degraded stimuli and normal stimuli. A possible explanation is that the context of a familiar narrative may increase attention and intelligibility, reducing degradation effects.