Page 42 - Spring 2019
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Hearing in the Glassruurn
subtle F0 differences between target and masker speech. also less able to use spatial cues to overcome the masking
These data highlight the importance of auditory experience associated with speech.
and mammtional effeds in learning how "3 segregate urge‘ In addition to sound source segregation, auditory scene analy-
fmm masker speech" sis depends on the ability to allocate and focus attention on
In addition to relying on acoustic voice differences between the target. Findings from studies using behavioral shadowing
talkers when listening in complex auditory environments, procedures provide indirect evidence that selective auditory
adults with normal hearing take advantage of the differ- attention remains immature well into the school-age years
ences in signals arriving at the two ears. These differences (e.g., Doyle, 1973; Wightman and Kistler, 2005). In a typical
provide critical information regarding the location of sound shadowing task, listeners are asked to repeat speech presented
sources in space, which, in turn, facilitates segregation of to one ear while ignoring speech or other sounds presented to
target and masker speech (e.g., Bregman, 1990; Freyman et the opposite ear. Children perform more poorly than adults
al., 2001). The binaural benefit associated with separating on these tasks, with age-related improvements observed into
the target and masker on the horizontal plane is often called the adolescent years (e.g., Doyle, 1973; Wightman and Kistler,
spatial release from masking (SRM). In the laboratory, SRM 2005). Moreover, children’s incorrect responses tend to be in-
is typically estimated by computing the difference in speech trusions from speech presented to the ear they are supposed
recognition performance between two conditions: the co- to disregard. For example, Wightman and Kistler (2005) asked
located condition, in which the target and masker stimuli are children (4-16 years) and adults (20-30 years) to attend to tar-
presented from the same location in space, and the spatial get speech presented to the right ear while disregarding mask-
separation condition, in which the target and masker stimuli er speech presented to both the right and left ears. Most of the
are perceived as originating from different locations on the incorrect responses made by adults and children older than 13
horizontal plane. For adults with normal hearing, SRM is years of age were due confusions with the masker speech that
substantially larger for speech recognition in a masker com- was presented to the same ear as the target speech. In contrast,
posed of one or two streams of speech than in a noise masker incorrect responses made by the youngest children (4-5 years)
(reviewed by Bronkhorst, 2000). tested were often the result of confusions with the masker
Several studies have evaluated SRM in young children and speed? resented "3 me °PP_ome ear as ‘he ‘afget speech‘ This
demonstrate a robust benefit of spatially separating the tar- r_esuh 15 mterpfifled as fhowmg that young dlfldren do not re-

. _ liably focus their attention on the target even in the absence of
get and masker speech (e.g., Litovsky, 2005, Yuen and Yuan, _ _
2014). Results are mixed, however, regarding the time course energetic masking‘
of development for SRM. Although Litovsky (2005) observed Although behavioral data suggest that selective auditory at-
adult-like SRM in 3-year-old children, other studies have re- tention remains immature throughout most of childhood,
ported a smaller SRM for children compared with adults, a a key li.rnitation of existing behavioral paradigms is that we
child/adult difference that remains until adolescence (e.g., cannot be certain to what a child is or is not attending. Poor
Yuen and Yuan, 2014; Corbin et al., 2017). In a recent study, performance on a shadowing task might reflect a failure of
Corbin et al. (2017) assessed sentence recognition for chil- selective attention to the target but is also consistent with an
dren (8-10 years) and adults (18-30 years) tested in a noise inability to segregate the two streams of speech (reviewed by
masker and in a two-talker masker. Target sentences were Sussman, 2017). This issue is further complicated by the bi-
always presented from a speaker directly in front of the lis- directional relationship between segregation and attention;
tener, and the masker was either presented from the front attention influences the formation of auditory streams (e.g.,
(co-located) or from 90° to the side (separated). Although a Shamma et al., 2011). Researchers have begun to disentangle
comparable SRM was observed between children and adults the independent effects of selective auditory attention by
in the noise masker, the SRM was smaller for children than measuring auditory event-related brain potentials (ERPs)
adults in the two-talker masker. In other words, children to both attended and unattended sounds (e.g., Sussman and
benefitted from binaural difference cues less than adults in Steinschneider, 2009; Karns et al., 2015). The pattern of re-
the speech masker. This is important from a functional per- sults observed across studies indicates that adult-like ERPs
spective because it means that not only are children more associated with selective auditory attention do not emerge
detri.rnentally affected by background speech, but they are until sometime after 10 years of age, consistent with the time
4|: 1 AI:uuI:l:I Tbday 1 Spring 2019

















































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