Using prosody to resolve temporary syntactic ambiguities in speech production: acoustic data on brain-damaged speakers

Abstract

Left hemisphere brain lesions resulting in aphasia frequently produce impairments in speech production, including the ability to appropriately transmit linguistic distinctions through sentence prosody. The present investigation gathered preliminary data on how focal brain lesions influence one important aspect of prosody that has been largely ignored in the literature - the production of sentence-level syntactic distinctions that rely on prosodic alterations to disambiguate alternate meanings of a sentence. Utterances characterizing three distinct types of syntactic ambiguities (scope, prepositional phrase attachment, and noun phrase/sentential complement attachment) were elicited from individuals with unilateral left hemisphere damage (LHD), right hemisphere damage (RHD), and adults without brain pathology (NC). A written vignette preceding each ambiguous sentence target biased how the utterance was interpreted and produced. Recorded productions were analysed acoustically to examine parameters of duration (word length, pause) and fundamental frequency (F₀) for key constituents specific to each of the ambiguity conditions. Results of the duration analyses demonstrated a preservation of many of the temporal cues to syntactic boundaries in both LHD and RHD patients. The two interpretations of sentences containing 'scope' and 'prepositional phrase attachment' ambiguities were differentiated by all speakers (including LHD and RHD patients) through the production of at least one critical temporal parameter that was consistent across the three groups. Temporal markers of sentences containing 'noun phrase/sentential complement attachment' ambiguities were not found to be encoded consistently within any speaker group and may be less amenable to experimental manipulation in this manner. Results of F0 analyses were far less revealing in characterizing different syntactic assignments of the stimuli, and coupled with other findings in the literature, may carry less weight than temporal parameters in this process. Together, results indicate that the ability to disambiguate sentences using prosodic variables is relatively spared subsequent to both LHD and RHD, although it is noteworthy that LHD patients did exhibit deficits regulating other temporal properties of the utterances, consistent with left hemisphere control of speech timing.

• Speech Production Prosody Syntactic Ambiguity Brain Damage Acoustic Analysis