Page 40 - Spring 2019
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Hearing in the Glassruurn
is mature by term birth, if not earlier (e.g., Abdala, 2001).
Neural transmission through the auditory brainstem appears
to be slowed during early infancy, but peripheral encoding
of the basic properties of sound approaches the resolution
observed for adults by about six months of age (reviewed by
. . I Eggermont and Moore, 2012; Vick, 2018).
A competing noise masker can interfere with the peripheral
/ encoding of target speech if the neural excitation produced
by the masker overlaps with the neural representation of the
“M target speech. This type of masking can be more severe in
children and adults with sensorineural hearing loss than in
Figure 1. This curtann illustrates the cacktuil puny piaelein in the time with Mimi l1WiI*8- sensorineural hearing 1055 is 0f-
classraam. In this example, acaustic wavefamis are prnduced by ten due to the loss of outer hair cells in the cochlea (reviewed
three samees: (1 ) mlise is prndueeii by u camputer prajeetar in the by Moore, 2007). As mentioned above, outer hair cell loss
ClflSSi‘Wm: (2) 5P9ecli is Pmdnced ii)’ the iellcheri and (3) SW55’! is degrades the peripheral encoding of the frequency, inten-
piaauceaay twn classmates wha ate ulsa talking. The fumiamental Sim mdtempoml features ofspmih Which, inmm impacts
pmlllem is that the acaustic wave/arms prnduced by all three saimd . . .
saurces caineine in the aii befare arrivingut the students’ ems. TafnI- masked ‘Peed’ re°°3“‘t‘°“; indeed‘ m“it‘Pi? researchers
law the teachers vaice, students must “heat am‘ and attend ta their haVe demonstrated an association between estimates 0r Pe-
teacher while disregarding the saunas pmduced by all nther sauiees. ripheral encoding and Performance on Sveech-in-noise tasks
  for adults with sensorineural hearing loss (e.g., Dubno et al.,
_ _ _ 1984; Frisina and Frisina, 1997).
lmmatunty at any stage of processing can impact the extent
to which students in the classroom hear and understand the Additional eVidence that cornPeting noise interferes with
target voice. For example, spectral resolution refers to the the PercePtual encoding of sPeech cornes from the results or
ability to resoive thg ii-idividuai frgqugncy components of 3 studies evaluating consonant identification in noise by adults
complex sound. Degraded spectral resolution is one conse- (e-Sn Miller and NicelY— i955? Pllatak Et al., 2003)- Consonant
quence of congenital hearing loss, specifically sensorineural identification is cornPrornised in a systematic Way across
hearing loss caused by damage to the outer hair cells in the individuals With norrnal hear ing when cornPetinS noise is
cochlea. This degraded peripheral encoding may reduce au- Presentv Presurnaoly because Patterns orexcitation Produced
dibility of the target speech, making it impossible for adults is)’ the target consonants and masking noise oVerlaP on the
or children with sensorineural hearing loss to perform audi- hasilaf Ineffllsffiflfi (Mil-lift l947)- in the classroorn ei‘arnPle
tory scene analysis. Perhaps less obvious, immature central shown in Figure 1: 0Vei'laP in excitation Patterns between
auditory processing could result in the same functional out- sPeech Produced oY the teacher and noise Produced oY the
col-mg in 3 child with normal hearing For examP1g_ gig Pg)‘. projector can result in an impoverished neural representa-
ceptual consequence of a failure to selectively attend to the tion or the teachers sPoken rnessagei although this dePends
spegch stream Producgd by the tgachgr, while ignoring C1355. on the relative levels of the two sources and distance to the
mates’ spegch, is rgducgd spegch in-idei-5:31-,ding_ evgn when listener. The term energetic masking is often used to describe
the peripheral encoding of the teacher’s speech provides all the PercePtual consequences otthis Phenornenon (reviewed
the cues required for recognition. by Brungartv 2005)‘
Despite mature peripheral encoding, school-age chil-
Maturation of Peripheral Encoding dren have more difliculty understanding speech in noise
Accurate peripheral encoding of speech is clearly a prerequi- compared with adults. For example, 5- to 7-year-old chil-
site for speech recognition. However, sensory representation dren require a 3-6 dB more favorable signal-to-noise ratio
of the frequency, temporal, and intensity properties of sound (SNR) than adults to achieve comparable speech detection,
does not appear to limit auditory scene analysis during the word identification, or sentence recognition performance
school-age years. The cochlea begins to function in utero, be- in a speech-shaped noise masker (e.g., Corbin et al., 2016).
fore the onset of visual functioning (Gottlieb, 1991). Physio- Speech-in-noise recognition gradually improves until 9-10
logical responses to sound provide evidence that the cochlea years of age, after which mature performance is generally ob-
as 1 AI:uulI:l:l Tbday 1 Spring 2019

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