Auditory function and cerebral dominance

Auditory function and cerebral dominance

Auditory function and cerebral dominance
Auditory function and cerebral dominance

Auditory function and cerebral dominance

Structural and functional asymmetries

Ever since Orton and Travis’s theory (Orton, 1927; Travis, 1931) of stuttering arising due to incomplete cerebral lateralization, the search for factors linking known differences in hemispheric processing with stuttering has remained a strong research trend. We also know that where hemispheric imbalance has been confirmed in recent studies using modern brain imaging techniques, areas subserving motor speech and language functions have been implicated (e.g., Fox, Ingham, Ingham, Zamarripa, Xiong, & Lancaster, 2000; Neumann et al., 2003). There is also evidence that differences in the auditory processing capabilities in those who stutter can be traced to differences in cerebral dominance. Dichotic listening studies  indicate that people who stutter may be less able to process linguistic information when presented to the right ear, in the face of a simultaneous competing linguistic message presented to the left ear. The functional neuroanatomy of those who stutter may differ from those who do not stutter with regard to auditory processing factors (Molt, 2003; Rastatter, Stuart, & Kalinowski, 1998; Salmelin, Schnitzler, Schmitz, Jäncke, Witte, & Freund, 1998). There is recent evidence too that there may be structural differences between brain centres involved in the processing of speech and language (Foundas, Corey, Angeles, Bollich, Crabtree-Hartman, Heilman, 2003; Foundas et al., 2004; Jänke et al., 2004). Using magnetic resonance imaging (MRI; ) Jänke et al. (2004) found increased masses in right-sided structures, in contrast to the typical leftsided asymmetry seen in nonstuttering control speakers. The superior temporal gyrus showed increased volume: a hemispheric imbalance that Jänke et al (2004) believe is related to persistent developmental stuttering
 Stuttering and auditory processing 51They conclude that the composition of the auditory cortex is different to that of nonstutterers, but they do add the caveat that (as with neurological studies that have implicated speech processing) it is not known whether these structural differences reflect the cause of stuttering, or an adaptation of the individual to it. Foundas et al. (2004) also noted that some adults who stutter have atypical rightsided planum temporale (PT) anatomy. They subsequently tested two groups of adults who stuttered, one of which had atypical PT anatomy, the other, normal left-sided PT anatomy, against a control group of nonstuttering speakers under both NAF (no altered feed-back) and DAF. The group with abnormal PT anatomy was found to have greater stuttering at baseline than the normal PT group, and recorded significantly reduced stuttering under DAF. The normal PT group, on the other hand did not experience any significant improvement in speech fluency. The authors conclude that abnormal PT anatomy might be a risk factor for developmental stuttering in some individuals. They tentatively speculate that this abnormal anatomy may alter speech feedback, allowing DAF to compensate
If this finding is verified in subsequent studies, this could go some way toward explaining the varied successfulness of commercially available altered auditory feedback devices 

 

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