Handout 8: Models and Theories of Speech Production

Question 1

what are the 5 problems involved in constructing a model of speech production?

Answer 1

1. Degrees of freedom problem
2. Unit of speech problem
3. Serial order problem
4. Context-sensitivity problem
5. Role of feedback problem

Question 2

describe the degrees of freedom problem

Answer 2

• many movements the respiratory, phonatory, articulatory systems do to produce speech
• each diff muscle contraction constitutes a degree of freedom
• total # of possible degrees of freedom is enormus
• speech motor sys much somehow control them all

Question 3

how many degrees of freedom are estimated in the speech production sys?

Answer 3

about 70 muscular degrees

Question 4

what two models have been proposed to reduce the total number of degrees of freedom to a smaller # of controlled variables?

Answer 4

coordinative structures

motor programs/internal models/ or schema

Question 5

coordinative strutures suggests that

Answer 5

groups of muscles are linked together into functional groups to perform a specific taak

Question 6

motor programs/internal models/schema suggests that

Answer 6

the commands to the muscles and articulators for a particular sound or feature are stored/run like a computer program

Question 7

what is the unit of speech prob?

Answer 7

asks what is the basic element that is controlled in speech

Question 8

what are the two categories of basic elements of speech suggested by research, example of each?

Answer 8

prearticulatory representation units (ex. syllables, phonemes, allophones), and motor realization units (ex. spacial articulatory targets, motor/muscle commands)

Question 9

what does research suggest in terms of the unit of speech prob

Answer 9

evidence points to a phoneme or syllable sized unit of speech organization

Question 10

what is the serial order prob?

Answer 10

asks: how are the basic units sequenced or assembled
- speech is a seq of elements and order is important for meaning

Question 11

what are spoonerisms? what do they provide evidence for?

Answer 11

mistakes in serial order of phonemes and words in everyday speech

types of errors also occur in post stroke speech disorders

provides evidence of a seq mechanism and the potential importance of the phoneme or syllable as the basic element of speech

Question 12

describe the context sensitivity prob

Answer 12

the production of a sound varies w context in which it is produced - there can be variability in sound production despite consistent sound perception

Question 13

describe coarticulation

Answer 13

a feature of one sound spreads into the articulation of an adjacent or earlier sound

Question 14

how is coarticulation accounted for in models?

Answer 14

look ahead mechanism –> scans planned seq and determines which features are free to vary - more efficient

Question 15

describe suprasegmental/prosodic effects and give examples

Answer 15

the first dimension in each of these 4 contrasts is associated with larger articulatory movements and ‘articulatory undershoot’ often associated with second dimension

• loud vs. soft speech

    - stressed vs. unstressed syllables 
  
    - slow vs. fast speech 
  
    - clear vs. casual speech

Question 16

describe the role of feedback problem

Answer 16

Feedback refers to the transfer of part of the output of a system back to the input to regulate and correct any errors in the output.

 How important is feedback in speech production? Is it essential?

Question 17

what are the 4 stages of feedback in motor control

Answer 17

first stage: error detected by comparing intended and actual movement

second stage: neural command generated to correct

third stage: transmission of correction to muscle

fourth stage: muscle contraction

Question 18

servomechanism + how its related to speech prod

Answer 18

uses feedback to regulate a sys
ex. thermostat

proposed a servomechanism of speech prod to explain stuttering in 1970s

Question 19

where does most of the evidence come from for the possible role of sensory feedback in speech prod?

Answer 19

sensory perturbation effects (aka blocking feedback)

Question 20

how does delayed auditory feedback effect speech

Answer 20

• delays at 50-150msec can cause slow speech

   - delays at 200-400msec can cause dysfluencies (can be overcome with practice)

Question 21

how does masking noise effect speech

Answer 21

louder speech - lombard effect

Question 22

how does filtered speech feedback effect speech

Answer 22

• small changes; higher pitch and decreased nasal resonance

   - speakers attempting to restore high frequency info

Question 23

how does altered intensity or pitch shifts feedback effect speech

Answer 23

speakers attempt to restore altered intensity or pitch

Question 24

how is speech effected in those that are adventitiously deafened speakers

Answer 24

• little immediate effect on intelligibility

   - speech deteriorates gradually but significantly over several months or years (leads to eventual consonant & vowel distortions, prosodic abnormalities, interarticulatory timing errors)

Question 25

so how does auditory feedback effect speech?

Answer 25

Moment-to-moment auditory feedback does not appear to be required for intelligible speech. However auditory feedback does appear to be important for the long-term maintenance of coordinated and intelligible speech.

Question 26

how does perturbation effect oral sensory feedback in speech production

Answer 26

• bite blocks (or pipe speech) & pseudo palates are compensated for almost immediately and do not seriously distort speech

Question 27

how does oral anaesthesia effect speech production

Answer 27

relatively minor effects on speech

Question 28

how does trigeminal sesnory neuropathy effect speech production

Answer 28

• permanent loss of oral sensory info
  • associated with significant speech distortions

Question 29

so how does oral sensory feedback effect speech production?

Answer 29

Similar to auditory feedback, speech does not appear to depend critically on continuous oral sensory feedback but prolonged sensory loss can lead to significant speech disturbances.

Question 30

so how is auditory and oral sensory feedback used then in speech production?

Answer 30

Sensory feedback may be used to maintain a set of internal standards for speech movements. These internal standards may only require periodic updates. OR, the speech system may only use feedback to detect and respond to disruptions or perturbations in the system.

Question 31

describe what a feedforward mechanism is

Answer 31

• some models of speech suggest that information about speech motor commands are monitored directly or via a parallel internal circuit
  • thus, errors in motor signals can be rapidly detected and corrected

Question 32

how may a feedforward mechanism work in speech

Answer 32

some models propose that feedforward processes may be primary once speech is developed; feedback may be needed to establish feedforward processes and to deal with short-term perturbations of feedback

Question 33

some speech disorders are proposed to develop a deficit in ______ processes (eg. Parkinson’s disease, stuttering) and become more dependent on _____ processes

Answer 33

feedforward, feedback

Question 34

what do motor programs or open loop control models propose?

Answer 34

• a plan or a prescription for a movement or action
  • in its extreme form a motor program makes no use of peripheral feedback
  • less extreme models combine motor programs and feedback mechanisms

Question 35

describe schema theory

Answer 35

• schema utilize current sensory information and also previously learned

      relationships among movement outcomes, control signals, and initial conditions 
  
    - the schema are used to prepare and execute a motor program

Question 36

Describe DIVA

Answer 36

Directions into velocities of articulators

a feedforward control system, involving premotor and primary motor cortex and the cerebellum, works in concert with auditory and somatosensory feedback control systems that involve both sensory and motor cortical areas

The basic unit is proposed to be articulatory velocity and position maps for speech sounds.