Abstract
Speech production difficulties are apparent in people who stutter (PWS). PWS also have difficulties in speech perception compared to controls. It is unclear whether the speech perception difficulties in PWS are independent of, or related to, their speech production difficulties. To investigate this issue, functional MRI data were collected on 13 PWS and 13 controls whilst the participants performed a speech production task and a speech perception task. PWS performed poorer than controls in the perception task and the poorer performance was associated with a functional activity difference in the left anterior insula (part of the speech motor area) compared to controls. PWS also showed a functional activity difference in this and the surrounding area [left inferior frontal cortex (IFC)/anterior insula] in the production task compared to controls. Conjunction analysis showed that the functional activity differences between PWS and controls in the left IFC/anterior insula coincided across the perception and production tasks. Furthermore, Granger Causality Analysis on the resting-state fMRI data of the participants showed that the causal connection from the left IFC/anterior insula to an area in the left primary auditory cortex (Heschl’s gyrus) differed significantly between PWS and controls. The strength of this connection correlated significantly with performance in the perception task. These results suggest that speech perception difficulties in PWS are associated with anomalous functional activity in the speech motor area, and the altered functional connectivity from this area to the auditory area plays a role in the speech perception difficulties of PWS.
Highlights
Speech and general motor programming deficits have both been reported in people who stutter (PWS) (Fox et al, 1996; Stager et al, 2005; De Nil et al, 2008; Lu et al, 2010a; Smith et al, 2012; Smits-Bandstra and De Nil, 2013; Smits-Bandstra and Gracco, 2015)
The questions this study addressed were as follows: (1) Are there any functional activity differences between PWS and controls in the speech motor areas during speech perception, and if so, are these functional activity differences in the speech motor areas coincident across speech perception and production tasks? (2) After the motor areas that show different functional activity between PWS and controls in speech perception and production tasks were identified, their relationship with speech perception areas was compared between PWS and controls
Independent two-sample t-tests on the behavioral reaction time (RT) data from the speech perception task showed that PWS had significantly longer RTs than controls in vowel judgment (VJ) [t(24) = 3.136, P = 0.004], but not in consonant judgment (CJ) [t(24) = 1.277, P = 0.214] (Figure 1)
Summary
Speech and general motor programming deficits have both been reported in people who stutter (PWS) (Fox et al, 1996; Stager et al, 2005; De Nil et al, 2008; Lu et al, 2010a; Smith et al, 2012; Smits-Bandstra and De Nil, 2013; Smits-Bandstra and Gracco, 2015). CWS do not show significant Mismatch Negativity amplitude in EEG potentials to syllables that have linguistic features that deviate from normal ones (Jansson-Verkasalo et al, 2014) Both adults and children who stutter do not show the expected left lateralized hemodynamic response when two aurally presented nonsense syllables that differ by one phoneme are compared (Sato et al, 2011). It is not known, whether such anomalous neural activity during speech perception for PWS is independent of, or related to, that seen in speech production
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