Examining Constraints on Speech Growth in Children with Cochlear Implants J' Bruce Tomblin The Unive

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Examining Constraints on Speech Growth in
Children with Cochlear Implants J. Bruce
TomblinThe University of Iowa
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Research Opportunities with Pediatric Cochlear
Implantation

• Most of the research on implants has been
  concerned with evaluating the effectiveness of
  this clinical intervention with regard to
• Improved auditory function
• Spoken communication development and function
• Improved quality of life

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Research Opportunities with Pediatric Cochlear
Implantation

• The CI population also provides opportunities to
  test theoretical issues
• Speech and language development using an
  alternate neural representation of the acoustic
  signal.
• Effects of differential timing of onset of
  auditory-linguistic experience relative to
  biological and cognitive development.

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Viewpoints on Developmental Constraints

• Constrained Periods
• a time in development in which the organism is
  particularly responsive to experience
• Critical Period
• A period with sharp onset and offset
• Response to experience limited to period and is
  irreversible.
• Sensitive Period
• A period with gradual onset and incomplete offset

Critical Period
open
close
Bruer, 2001
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Critical Periods and Language

• Lenneberg (1967) brain lateralization at puberty
  closes down the brain's ability to acquire
  language. (critical period)
• Pinker (1994) acquisition of a normal language
  is guaranteed for children up to the age of six,
  is steadily compromised from then until shortly
  after puberty, and is rare thereafter (sensitive
  period)
• Note that in both cases the interest is in the
  nature of the closing point.

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Mechanisms for CP/SP

• Maturational Processes
• Biologically driven events that cause the brain
  to become open or closed to experience.
• Timing is closely linked to physical maturation
  and thus to chronological age.
• Experience Dependent Processes
• The brain becomes more or less responsive to
  experience as a function of prior learning.
• Entrenchment results in biases toward some
  learning and against other learning accented
  speech in L2 adults.

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Rationale

• Speech development in the hearing child is
  typically mastered by 5 or 6 and those who fail
  to reach mastery by 8 or 9 years are unlikely to
  do so without help (Shriberg, Gruber,
  Kwiatkowski 1994).
• To what extent is this constraint on speech
  development determined by maturational or
  experience?
• Children receiving CIs in childhood will be
  delayed in speech development.
• Is speech sound development constrained by the
  childs chronological age?
• Does speech growth extend beyond the
  developmental period of 6 to 9 years of age?
• Is the attainment of a plateau in speech
  associated with chronological age or hearing age?
• Is speech sound development constrained by the
  childs length of hearing?

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Participants

• 41 Prelingually Deaf Children with 4 or more
  years of implant experience
• Average First Observation
• CA 3.28 (1.1) years
• Hearing Age 0.32 (0.53)
• Average Last Observation
• CA 9.72 (2.83)
• Hearing Age 6.76 (2.66) years
• Mean Age of Implantation
• 2.97 Years (SD 1.2) range 1.7-6.46

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Methods

• Speech elicited via a story retell
• Analysis
• Utterance is phonemically glossed using childs
  signed and spoken utterances in conjunction with
  story context.
• Childs spoken utterance transcribed phonetically
• Phoneme accuracy assigned according to
  correspondence between phonetic transcript and
  gloss standard.
• Percent phonemes correct determined by ratio of
  number of accurate phonemes/number of phonemes in
  gloss.

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Development of Phoneme Accuracy
Chronological Age
N41
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Characterizing Growth
Maximal Level of Performance
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Growth Heterogeneity

• Individuals who reach a plateau
• N 13 AOI 29 mo.
• Individuals who do not plateau
• N 28 AOI 38 mo.

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Group without Plateau

• Does growth continue past middle childhood (6-9
  years)?

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9 years of age
N29
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Children Followed Beyond 10 Years of Age
N13
13.3
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(No Transcript)
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Growth in Group without Plateau

• Growth does appear to persist after 9 years of
  age.
• In the 13 children followed into early
  adolescence there is little evidence of a clear
  closing of speech growth.
• Growth appears more closely related to amount of
  hearing experience than chronological age, thus a
  simple maturational account does not fit.
• No support for a critical period. Perhaps room
  for a sensitive period that is influenced by
  experience rather than maturation.

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Group with a Plateau

• Does the point of plateau appear to be linked to
  chronological age or length of hearing?

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Growth in Children who Reach Plateau
Average (90)
N13
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Variation in Point of Asymptote as a Function of
CA or Hearing Age
96.2
66.5
Coefficient of Variation
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Features of Growth in Children who Do Reach
Plateau

• These children had more rapid rates of growth
  than the non-plateau children.
• Is this a sign of a sensitive period?
• Is this evidence that fast learners will reach
  plateau faster?
• The age at plateau was within the age range of
  normal hearing children.
• The level of performance at plateau was below
  that of normals, but near ceiling.
• The point where plateau was reached was more
  consistently related to CA than Hearing Age.
• These results leave room for a type of
  maturational influence on speech development.

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Conclusions

• A strict critical period determined by
  maturational processes linked to chronological
  age does not operate for speech sound
  development.
• Growth in speech is linked to the amount of
  hearing and does not appear to be constrained by
  chronological age.
• Growth rates in older children may be slower,
  than younger children which may represent a
  sensitive period, however this may simply be a
  product of selection where only the slow learners
  remain in the non-plateau group.