Sensorimotor Contributions to Stuttering

Question 1

Stuttering Onset

Answer 1

• 60% cases have onset b/t 2-3.5 years (coincides w/ advancements in artic phono, morpho, syntax)
• 5-7 new words learned/day
• Neuroanatomical deficits (involve LEFT IFG)

Question 2

Language Complexity and Stuttering Onset Theory

Answer 2

• planning/speech production may rely on atypical neural pathways (inefficient for this precise/demanding task)
• demands grow greater for child to make longer complex utterances

Question 3

Spatiotemporal index (STI)

Answer 3

Measure of variability in articulatory movement when a sentence is said over and over

Question 4

Wave articulograph/MRI Data (2010)

Answer 4

WAVE sensors (coloured dots) overlaid on top of MRI photo of body

Question 5

STI and linguistic complexity

Answer 5

-stability decreases and linguistic complexity increased in PWS
-adults who stutter have speech motor system that is vulnerable to breakdown when language demands are high.
**More variability overall (in kids too but they are generally more variable)
UTTERANCE LENGTH alone made this differentiation

Question 6

Articulation

Answer 6

-2.5x more likely for CWS to have artic disorder than controls (some found no difference).. a lot of variability in children

Question 7

Speech Sound Production

Speech Motor Control System

Answer 7

• integration of auditory, somatosensory & motor information
• neural representations sotred in temporal, parietal and frontal lobes
• cerebellum, BG, brainstem support this

Question 8

The DIVA Model

Answer 8

Auditory feedback most important
Feedforward control system to artic muscles (cerebellus, primary motor cortex) via subcortical nuclei
Feedback control system:
Somatosensory & Auditory feedback via subcortical nuclei
-Each box corresponds to a set of neurons
-arrows: synaptic projections

Question 9

The Speech Sound Map

Answer 9

Neuroanatomic correlates:
-left ventral premotor cortex and the posterior inferior frontal gyrus
Function:
-LINK b/t sensory representation of speech sound and motor program for that sound
-neurons in this region are active during both production and perception of motor actions

Question 10

Learning To Speak

4 phases

Answer 10

• babbling
• imitation
• shaping
• rhythmic

Question 11

Babbling

Answer 11

• Establishing forward mapping

- random, reduplicated combo of motor somatosentory & auditory info

Question 12

Imitation

Answer 12

Try and reproduce limited set of sound sequences by audio-visual-to-artic mapping
-sensory info mapped to motor info

Question 13

Regions vs. points in imitation

Answer 13

• regions: allow for unified explanation of many speech production phenomena
• if discrete points, hard to move from one sound to another (brain would need representations for every variety of sound

Question 14

Imitation Steps

Answer 14

1. Model tries to make sound, activates speech sound map neurons corresponding to that sound
2. readout of feedforward commands results
3. 1st attempt for new sound, no tuned feedforward exists, auditory errors will occur, auditory feedback will shape attempt
4. Auditory error must be transformed into corrective commands in motoric/articulatory space
5. Each attempt to produce sound = updating of system, more accurate feedforward commands
6. Eventually feedforward commands sufficient to produce sound w/ little input from feedback loops

Question 15

Sensorimotor Control & Stuttering

2 hypotheses

Answer 15

1. Unstable or insufficiently activated internal representation of transformations that occur when central motor commands converted into speech
2. Motor control strategy that relies too much on afferent signals associated w/ time lags b/c feedforward system is unreliable

Question 16

Feedforward Control Deficits

Answer 16

Stuttering from diminished motor skills that need transition from feedback to feedforward control
-Over-reliance on feedback control ^ frequency of production errors

Question 17

Theory of Creating Stuttering Moment

Answer 17

• Feedforward - stable system from memory w/ detailed instructions on how to move articulators
• Feedback control - indirect and slow (detects/corrects production errors)

Hypothesis: Over reliance on feedback control = error accumulation, then a motor reset where system attempts to repair error by restarting current syllable

Evidence: people who stutter have errors in both fluent & disfluent speech, more errorful in general

Question 18

Over-Reliance on Auditory Feedback Summary

Answer 18

• Explains why sound/syllable repetitions likely occur on/after consonants (rapid formant transitions)
• Explains why repetitions are usually word-initial (auditory feedback not available, must rely on impaired feedforward commands)
• May explain childhood onset (improvement of impaired feedforward through learning/maturation, large changes in rate and complexity at age 2-5)

Question 19

Faulty auditory-to-motor mapping

Answer 19

• People who stutter may not be able to compensate for auditory or sensory error in speech as efficiently as fluent speakers b/d of deficient mappings
• Perturbation experiment
• When auditory perturbation, PWS less compensation (47% weaker), start later