Phrase-level prosody plays a crucial role in language processing and language development, as shown by studies on spoken language comprehension (Millotte et al. 2007), artificial grammar learning (Langus et al. 2012) and prosodic bootstrapping (Hohle 2009). Intonational phrase boundaries (IPB) mostly coincide with major syntactic boundaries. The Closure Positive Shift (CPS) indexes the perception of IPB, but it is still unclear whether this effect is triggered by prosodic information only (Pannekamp et al., 2005) or relies on syntactic knowledge (Mannel et al., 2013). This study investigated the CPS in IPB perception in European Portuguese, a language where pitch movements combined with boundary lengthening are mostly confined to IP-edges, namely the IP-final stressed syllable and the boundary syllable. Delexicalized sentences were used to address the debate of whether the CPS is, or not, purely prosody-driven. Results showed a CPS in response to IPB in delexicalized utterances with no syntactic information (ANOVA midline: F(1,23)=15.48, p<.001, eta-squared=0.52). Moreover, the CPS response was stronger and later when lexical stress and IPB overlapped, than when lexical stress preceded IPB. These findings indicate that brain responses to IPBs are purely prosody-driven, and are modulated by the distribution of nuclear prominence and prosodic boundary cues.

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