Abstract
Developmental stuttering is a speech disorder in fluency characterized by repetitions, prolongations, and silent blocks, especially in the initial parts of utterances. Although their symptoms are motor related, people who stutter show abnormal patterns of cerebral hemispheric dominance in both anterior and posterior language areas. It is unknown whether the abnormal functional lateralization in the posterior language area starts during childhood or emerges as a consequence of many years of stuttering. In order to address this issue, we measured the lateralization of hemodynamic responses in the auditory cortex during auditory speech processing in adults and children who stutter, including preschoolers, with near-infrared spectroscopy. We used the analysis–resynthesis technique to prepare two types of stimuli: (i) a phonemic contrast embedded in Japanese spoken words (/itta/ vs. /itte/) and (ii) a prosodic contrast (/itta/ vs. /itta?/). In the baseline blocks, only /itta/ tokens were presented. In phonemic contrast blocks, /itta/ and /itte/ tokens were presented pseudo-randomly, and /itta/ and /itta?/ tokens in prosodic contrast blocks. In adults and children who do not stutter, there was a clear left-hemispheric advantage for the phonemic contrast compared to the prosodic contrast. Adults and children who stutter, however, showed no significant difference between the two stimulus conditions. A subject-by-subject analysis revealed that not a single subject who stutters showed a left advantage in the phonemic contrast over the prosodic contrast condition. These results indicate that the functional lateralization for auditory speech processing is in disarray among those who stutter, even at preschool age. These results shed light on the neural pathophysiology of developmental stuttering.
Highlights
Developmental stuttering is a disorder of speech fluency characterized by involuntary repetitions, prolongations, and silent blocks, especially in the initial parts of utterances
A subject-by-subject analysis revealed that not a single subject who stutters showed a left advantage in the phonemic contrast over the prosodic contrast condition.These results indicate that the functional lateralization for auditory speech processing is in disarray among those who stutter, even at preschool age
Results of two-way analysis of variance (ANOVA), with condition and side as within-subject factors in each adult group showed that the people who stutter (PWS) exhibited no significant interaction or main effects for the two factors [F(1,9) = 0.30, p > 0.10; F(1,9) = 0.02, p > 0.10; F(1,9) = 3.33, p > 0.10, interaction, condition, side respectively], whereas the control (Ctrl) group exhibited a significant interaction [F(1,9) = 12.07, p < 0.01] but no effects for condition [F(1,9) = 0.32, p > 0.10] or side [F(1,9) = 0.05, p > 0.10], suggesting that the activations in the left and the right differed between the conditions only in the control group (Figure 3A)
Summary
Developmental stuttering is a disorder of speech fluency characterized by involuntary repetitions, prolongations, and silent blocks, especially in the initial parts of utterances. It typically starts between 2 and 6 years of age, occurring in 4–5% of all preschool children (Bloodstein, 1995; Yairi and Ambrose, 1999). There is evidence, that linguistic demands and changes in auditory inputs affect stuttering frequency. It has been reported that the phonological complexity affects the speech motor dynamics in adults who stutter (Smith et al, 2010). Better fluency can be induced with changes in the auditory input, such as delayed or frequencyaltered auditory feedback of speech, choral reading (in unison with other speakers), masking by white noise, and external rhythmic cues (e.g., metronome)
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