Lecture 2 Flashcards
Describe the growth of the tectorial membrane.
Tectorial membrane develops and matures by the end of gestation.
What are the implications for hearing in regards to tectorial membrane development?
Cochlear frequency sensitivity is not present until 30-35 weeks gestation due to development of tectorial membrane.
- Mid-freq region first to develop and connect with the brainstem
- 6 months after birth, high– and low-freq thresholds continue to improve
Low threshold signal detection and cochlear frequency selectivity are not evident until late stages of gestation.
When do we first hear?
Anatomic connections of the cochlea to brain are complete ~10-20 weeks before birth.
- ABR waveforms measured in 15-wk premature neonates
- Startle reflexes documented at 24-25 wks gestational age
How does plasticity play a role in binaural hearing?
Medial and lateral nuclei of superior olive and medial nucleus of the trapezoid body receive input from both cochleas.
Unilateral hearing loss:
- Nuclei receive two inputs originating from the same side
- Changes the brainstem and midbrain response
How is plasticity relevant for early intervention considerations?
Early hearing loss can impact binaural auditory development.
- Possible problems in language development
- Make every attempt to normalize hearing during early postnatal years
What can happen at the level of the cortex if hearing loss is present?
Cortex can be rewired and other modalities are recruited in place of the auditory modality.
- When one modality is absent, related cortical areas are available to process what is missing
How does speech perception develop from birth to 6 months?
Full-term newborns have over 2 months auditory experience.
- Evidence of early encoding of speech info. to memory, particularly suprasegmental info.
- Newborns can distinguish between native and nonnative languages
What evidence is there to demonstrate that infants perceive suprasegmentals?
DeCasper & Spence (1986)
- Looked at newborns’ and fetuses’ memory of mother’s speech
- Mothers read nursery rhyme 3 times/day starting 6 weeks before due date
- Newborns demonstrated preference for familiar nursery rhyme over a new nursery rhyme
- 4 weeks is sufficient for fetuses to encode some properties of a nursery rhyme
Granier-Deferre et al. (2011)
- Fetuses exposed to piano melody at 35-37 weeks showed memory of melody 6 weeks later
Kruger & Garvan (2014)
- 38 week fetuses demonstrated memory of nursery rhyme that was regularly presented from 28-34 weeks gestation
What is segmental information?
Acoustic properties of speech that differentiate phonemes
How do young infants perceive segmental information?
They demonstrate sensitivities to fine-grained changes in segmental info. despite lack of experience with high frequencies (filtering in utero)
How do infants perceive categorical information?
Infants may have some initial auditory sensitivity to particular acoustic-phonetic cues, but are not rigid and can be influenced by linguistic input
- Many consonant contrasts are perceived categorically but vowels are perceived more continuously
What are the effects of language experience on speech discrimination?
Younger infants can discriminate phonemic contrasts that are difficult for adults, but 10-12 month olds could only discriminate contrasts that were linguistically relevant
- This suggests that consonant discrimination is affected by language input
What is the Universalist view of language experience on speech discrimination?
Infants are born able to discriminate any phonemic contrast that could potentially be relevant to any of the world’s languages.
Then, with experience, they lose the ability to discriminate contrasts that are not relevant for their language
What are the limitations of the Universalist view?
Doesn’t take into consideration subphonemic info that is relevant for other aspects of speech perception and language acquisition
- Allophones (context dependent variants of a phoneme)
- E.g., aspirated /p/ in “port” vs unaspirated in “sport”, “night rates” vs “nitrates”
Some contrasts, rather than being discriminable universally during early infancy, require language experience before they can be discriminated
- Swedish [a] and [a] in Swedish-learning 6-12 month olds (Lacenda, 1993)
- 4.5-6 month olds did not discriminate a distinctive Spanish VOT contrast (Lasky et al., 1975)
Recent work suggests that VOT boundaries shift to what is appropriate for the ambient language ~8-10 months of age (Burns et al., 2007, Hoonhorst et al., 2009,Liu & Kager, 2015)
- Other studies have demonstrated that discrimination of some contrasts improves with language experience from infancy through adulthood (Narayan et al., 2010; Sato et al., 2010)
- E.g., /d/ vs./ ð/ in English-learning infants and children
What is recognition memory?
Recognition is a very basic form of learning
- To recognize something, it must be encoded in memory.
- Has been studied more in visual than auditory domain
- Recognition memory improves significantly during 1st year of life and correlates with language and cognitive outcomes (Rose et al., 1991, 1992)
Examples of infant recognition memory for speech
-Preferences for mother’s voice & native language
Work with older infants suggests that infants’ representations of speech sounds become more generalizable with experience and development
