Handout 8: Models and Theories of Speech Production Flashcards
what are the 5 problems involved in constructing a model of speech production?
- Degrees of freedom problem
- Unit of speech problem
- Serial order problem
- Context-sensitivity problem
- Role of feedback problem
describe the degrees of freedom problem
- 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
how many degrees of freedom are estimated in the speech production sys?
about 70 muscular degrees
what two models have been proposed to reduce the total number of degrees of freedom to a smaller # of controlled variables?
coordinative structures
motor programs/internal models/ or schema
coordinative strutures suggests that
groups of muscles are linked together into functional groups to perform a specific taak
motor programs/internal models/schema suggests that
the commands to the muscles and articulators for a particular sound or feature are stored/run like a computer program
what is the unit of speech prob?
asks what is the basic element that is controlled in speech
what are the two categories of basic elements of speech suggested by research, example of each?
prearticulatory representation units (ex. syllables, phonemes, allophones), and motor realization units (ex. spacial articulatory targets, motor/muscle commands)
what does research suggest in terms of the unit of speech prob
evidence points to a phoneme or syllable sized unit of speech organization
what is the serial order prob?
asks: how are the basic units sequenced or assembled
- speech is a seq of elements and order is important for meaning
what are spoonerisms? what do they provide evidence for?
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
describe the context sensitivity prob
the production of a sound varies w context in which it is produced - there can be variability in sound production despite consistent sound perception
describe coarticulation
a feature of one sound spreads into the articulation of an adjacent or earlier sound
how is coarticulation accounted for in models?
look ahead mechanism –> scans planned seq and determines which features are free to vary - more efficient
describe suprasegmental/prosodic effects and give examples
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
describe the role of feedback problem
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?
what are the 4 stages of feedback in motor control
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
servomechanism + how its related to speech prod
uses feedback to regulate a sys
ex. thermostat
proposed a servomechanism of speech prod to explain stuttering in 1970s
where does most of the evidence come from for the possible role of sensory feedback in speech prod?
sensory perturbation effects (aka blocking feedback)
how does delayed auditory feedback effect speech
- delays at 50-150msec can cause slow speech
- delays at 200-400msec can cause dysfluencies (can be overcome with practice)
how does masking noise effect speech
louder speech - lombard effect
how does filtered speech feedback effect speech
- small changes; higher pitch and decreased nasal resonance
- speakers attempting to restore high frequency info
how does altered intensity or pitch shifts feedback effect speech
speakers attempt to restore altered intensity or pitch
how is speech effected in those that are adventitiously deafened speakers
- 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)
so how does auditory feedback effect speech?
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.
how does perturbation effect oral sensory feedback in speech production
- bite blocks (or pipe speech) & pseudo palates are compensated for almost immediately and do not seriously distort speech
how does oral anaesthesia effect speech production
relatively minor effects on speech
how does trigeminal sesnory neuropathy effect speech production
- permanent loss of oral sensory info
- associated with significant speech distortions
so how does oral sensory feedback effect speech production?
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.
so how is auditory and oral sensory feedback used then in speech production?
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.
describe what a feedforward mechanism is
- 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
how may a feedforward mechanism work in speech
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
some speech disorders are proposed to develop a deficit in ______ processes (eg. Parkinson’s disease, stuttering) and become more dependent on _____ processes
feedforward, feedback
what do motor programs or open loop control models propose?
- 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
describe schema theory
- 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
Describe DIVA
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.
