Chapter 7 Flashcards
Cerebral Dominance Theory
Proposed stuttering was caused by a lack of cerebral dominance
Left and right hemispheres compete for control of speech movements
Asynchrony (mistiming) of neural impulses from both sides of the brain disrupts speech fluency
Differences in brain structure
Wernicke’s area smaller in LH for PWS More gyri in Sylvian (LH) region in PWS Higher white matter volume in RH Reduced white matter integrity in LH Deficiencies in LH gray matter volume **Most research done w/ adults!
Recent research with kids…
Reduced white matter integrity in LH
Persistent and Recovered CWS: lower gray matter volume in LH speech areas
But…only CWS who persisted showed lower white matter integrity in LH
No differences in RH activity and no asymmetry between hemispheres.
Neuro-physiological differences
Overactivation of motor areas Especially in RH Lower activity in auditory areas Auditory suppression bilaterally Anomalous RH activity and lateralization Decreased connectivity of white matter Lower activity in basal ganglia and cerebellum More activation in anterior cingulated cortex
Auditory Perceptual Theory
Proposed stuttering was caused by defective auditory feedback
The speaker expects to hear sound earlier than their auditory system feeds it back
The speaker waits (prolongs) or repeats trying to correct the delay
Role of audition
Speech control relevant to audition Deaf individuals The Lombard effect Delayed Auditory Feedback Frequency Altered Feedback Dichotic listening studies
*Deaf individuals are less likely to stutter
Lombard effect: talking with a lot of background effect- less stuttering in noisy situation where they have to talk more loudly
Right ear preference: because of crossover of the language dominant center from the left hemisphere
Less of a right ear preference for people who stutter
Studies that look at language processing in the brain:
PWS as they are listening to language tasks
How the brain responded to intentional errors in speech
Semantic and syntactic processing seemed to be less differentiated in PWS than people who don’t
PWS seem to have atypical structure and function in language areas of the brain. And atypical behavior in PWS in response to just hearing language.
*Motor learning studies: Purdue
Repeat the same sentence over and over- normally not a lot of variability
Look at stability of articulators between space and time (spatial temporal output)
People who stutter are more variable in terms of stability of repeated movements, especially if the sentence is more complex
Adults should not be variable, should be consistent but that is not the case with PWS
Even differences in hand writing in PWS; may be a motor issue in general
More variability of motor movements spoken and tasks with the hands, may be more than just speech
Motor coordination can be de-stabilized in PWS especially with more complex language
Sensory/Motor Dysfunction
Most obvious part of stuttering
Slower response times (vocal or manual)
Abnormal movement patterns in jaw, tongue, and larynx (even in fluent speech)
E.g., timing, muscle activation sequencing force of movements, abnormal breathing patterns, slower rate
Brainstem Reflexes: Disorder of Movement Theory
Proposed stutterers have reduced tolerance for a range of oral movements
If the range is exceeded, brainstem reflex management is upset
Afferent and efferent signals of speech muscles conflict so stuttering occurs
DIVA (Directions into Velocities of Articulators) Model
Stuttering is due to a disorder of sensorimotor speech control
PWS have unreliable feedforward systems so they rely excessively on controlling speech via feedback
Fluency is disrupted by the attempts to adjust speech movements after commands have been issued
Conclusions??
Is stuttering an impairment in the vocal organism itself (peripheral nervous system)?
Or, it is a problem of vocal planning and initiation (central nervous system)?
**Think about the ameliorating conditions
RH overactivity may be compensatory
*Act, sing, accent, DAF, etc and don’t stutter (problem in motor system itself? Can’t be)
CNS- planning and programming to change motor output
Internal trigger for the speech task is off, this explains why an external trigger might help (DAF)
RH over activity is compensatory because of structural and functional deficits in the LH
Putting it all together…
Genetic and neurological research combined with sensory-motor dysfunctions in PWS point to a UNSTABLE/UNRELIABLE neuromotor system for speech
But, don’t be depressed
Plasticity of the brain is possible
Many children develop a workaround (Chang et al. 2008)
Following treatment, stronger left hemisphere activity
Also, gray matter volume can increase with practice of certain behaviors
*Plasticity possible for adults and children, any new thing you do or practice changes the brain.
You can change the size and volume of gray matter in the brain and increase connections of white matter by practicing new things
SLPs change people’s brains
Less right hemisphere activation and more left hemisphere activation after therapy, more and stronger connections in the left hemisphere after treatment
