Adults with cochlear implants can use prosody to determine the clausal structure of spoken sentences

Abstract

Speech prosody, including pitch contour, word stress, pauses, and vowel lengthening, can aid the detection of the clausal structure of a multi-clause sentence and this, in turn, can help listeners determine the meaning. However, for cochlear implant (CI) users, the reduced acoustic richness of the signal raises the question of whether CI users may have difficulty using sentence prosody to detect syntactic clause boundaries within sentences or whether this ability is rescued by the redundancy of the prosodic features that normally co-occur at clause boundaries. Twenty-two CI users, ranging in age from 19 to 77 years old, recalled three types of sentences: sentences in which the prosodic pattern was appropriate to the location of a clause boundary within the sentence (congruent prosody), sentences with reduced prosodic information, or sentences in which the location of the clause boundary and the prosodic marking of a clause boundary were placed in conflict. The results showed the presence of congruent prosody to be associated with superior sentence recall and a reduced processing effort as indexed by the pupil dilation. The individual differences in a standard test of word recognition (consonant-nucleus-consonant score) were related to the recall accuracy as well as the processing effort. The outcomes are discussed in terms of the redundancy of the prosodic features, which normally accompany a clause boundary and processing effort.

FIG. 1.

The percentage of content words reported correctly (left) and the percentage of complete sentences correctly recalled (right) for sentences heard with congruent, reduced, and conflicting prosody. The error bars are one standard error.

FIG. 2.

The categories of incorrect recalls in the conflicting prosody condition. The first two bars show the percentage of responses that formed grammatically coherent sentences, which had a major clause boundary at the lexico-syntactically defined position in the original sentence (syntax), or at the point that had been suggested by the prosodic marking (prosody). The remaining two categories were grammatical responses that did not have a clause boundary at either point and sentence fragments that did not form a meaningful utterance. The error bars are one standard error.

FIG. 3.

(Color online) (A) shows the time course of adjusted pupil dilations while listening to sentences with conflicting, reduced, and congruent prosody, and for the first 2 s of the 4-s silent interval between the end of a sentence and the signal to begin the sentence recall. Pupil sizes are shown relative to the pre-sentence baselines, further scaled as a percentage of the individuals' pupillary dynamic range (see the text). The vertical line at the zero-point on the abscissa is aligned with the sentence endings. (B) shows the mean adjusted pupil sizes over a 1-s time window beginning 400 ms after a sentence ending for each of the three prosody conditions [shaded area in (A)]. (C) shows these data, excluding the participants with CNC scores below 45% correct. The error bars are one standard error.

FIG. 4.

The mean adjusted pupil size in the period prior to the recall signal in each of the three prosody conditions plotted as a function of the individual participants' CNC-30 score. The formulas for the best fit linear regressions and Pearson correlations are shown in each case for the participants with CNC-30 scores greater than 45% (shaded areas).