Word tones cueing morphosyntactic structure: Neuroanatomical substrates and activation time-course assessed by EEG and fMRI

Abstract

Previous studies distinguish between right hemisphere-dominant processing of prosodic/tonal information and left-hemispheric modulation of grammatical information as well as lexical tones. Swedish word accents offer a prime testing ground to better understand this division. Although similar to lexical tones, word accents are determined by words' morphosyntactic structure, which enables listeners to use the tone at the beginning of a word to predict its grammatical ending. We recorded electrophysiological and hemodynamic brain responses to words where stem tones matched or mismatched inflectional suffixes. Tones produced brain potential effects after 136 ms, correlating with subject variability in average BOLD in left primary auditory cortex, superior temporal gyrus, and inferior frontal gyrus. Invalidly cued suffixes activated the left inferior parietal lobe, arguably reflecting increased processing cost of their meaning. Thus, interaction of word accent tones with grammatical morphology yielded a rapid neural response correlating in subject variability with activations in predominantly left-hemispheric brain areas.

Stem Tones Pre-activate Suffixes in the Brain

“…For Swedish, it has been suggested that tones on word stems (“word accents”) are used as cues to pre-activate upcoming suffixes (Roll et al. 2015). Suffixes that are invalidly cued by an incorrect tone have been seen to increase response times and lead to a P600 reprocessing effect in event-related potential (ERP) studies (Roll et al.…”

“…2013; Roll 2015; Roll et al. 2015). However, it is unclear whether this tone-morphology interaction is based on a direct association between tones and suffixes in the brain, independent of their association with lexical word stems, or whether the tone-suffix association is dependent on and tied to whole word forms.…”

“…2010, 2013, 2015; Roll 2015). In previous studies, this effect has been viewed as a positively charged effect for accent 2.…”

“…Data from Roll et al. (2015), however, has led to a re-evaluation of this view. There it was found that accent 1 stems gave rise to increased neural activity, as evidenced by a greater BOLD (blood-oxygen-level dependent) effect as well as greater gRMS (global root mean squares) amplitudes for accent 1 compared to accent 2 1.…”

“…In the fMRI investigation reported on in Roll et al. (2015), activation for accent 1 was found in BA47 in the inferior frontal gyrus (IFG), an area known to be involved in morphological processing. This effect—as well as an effect in primary and secondary auditory cortex—correlated with a gRMS peak at 136 ms after tone onset.…”