Interaction of right- and left-edge prosodic boundaries in syntactic parsing

This electrophysiological study investigated how right- and left-edge prosodic boundary tones interact in the processing of syntactic structure. Swedish sentences of the type ‘Peter hit Larry(NP2) and Jason(NP3) fell/hard…’ were used. A verb (‘fell’) requires a clause boundary between NP2 and NP3, whereas an adverb (‘hard’) implies continuation of the first clause, which incorporates NP3 as a coordinated object. The effects of right-edge prosody associated with NP2 and left-edge prosody associated with NP3 were tested. Results suggest interaction between prosodic right- and left-edge boundary cues both at the earliest stages of processing the left-edge boundary tone on NP3 and at the immediately following word category distinction. Right-edge boundary tones on NP2 yielded an early positive deflection (P200) and a later positivity (CPS). Left-edge tones on NP3 showed a P200 effect only if preceded by a right-edge boundary on NP2. In the absence of a prosodic right-edge boundary, left-edge tones instead yielded an early negativity (N100), suggesting that they were unexpected. At the following word category distinction point, adverbs, showing continuation of the first clause, produced an anterior negativity when preceded by both right- and left-edge prosodic boundaries. The negativity is thought to reflect detection of a syntactically incorrect word category. Syntactically un-preferred constructions with an adverb following NP3 received generally lower acceptability ratings and gave rise to a P600 effect in all conditions. Syntactically preferred constructions with verbs following NP3 showed a similar P600 only when not preceded by either right- or left-edge boundary tones.

Research highlights
► Right- and left-edge prosodic boundaries interact at various levels of sentence processing.
► Right-edge prosody influences early stages of auditory processing of left-edge boundary tones.
► Contiguous right- and left-edge boundaries have cumulative effects on parsing.
► Left-edge boundaries following right-edge boundaries activate a main clause structure.
► Adverbs contradicting an activated main clause structure yield anterior negativity.