Otitis media is the most common medical condition in early childhood and, certainly, the most frequent presenting concern in the pediatric audiology clinic. Approximately 90 percent of infants have at least one episode of middle ear disease within the first two years of life, and around one in three experience chronic or recurrent problems.
Most affected children show impaired sound detection because of reduced middle ear conduction efficiency, and many experience fluctuating acuity with changes in the composition, quantity, and location of the effusion. These hearing deficits represent a significant perceptual barrier, particularly in noisy or group situations, and often result in behavioral and communication difficulties.
Middle ear function typically returns to normal once the effusion has cleared, allowing sound detection to normalize, too. This doesn't necessarily mean, however, that functional hearing, especially speech perception, is also restored.
BINAURAL PROCESSING CUES
There is evidence that children with a history of otitis media may show figure–ground deficits for a number of years after the middle ear disorder has resolved ( Pediatrics 2003;112: 265-277 http://pediatrics.aappublications.org/content/112/2/265.abstract; Audiol Neurotol 2009;14:121-129 http://www.ncbi.nlm.nih.gov/pubmed/18852485).
The mechanisms underlying this processing deficit are not entirely clear, but it has been suggested that impaired or fluctuating hearing in early childhood may specifically affect the ability to combine inputs from the two ears.
For instance, disrupted perception of binaural timing cues has been shown in masking level difference (MLD) tasks, which measure the listener's ability to integrate interaural phase differences ( Audiology 1991;30:91-101 http://www.ncbi.nlm.nih.gov/pubmed/1877902).
The integration of subtle interaural timing, level, and spectral differences allows perception of the three-dimensional auditory environment and precise determination of sound direction.
In addition, sound localization cues may be used to improve speech perception in background noise when the target of interest and the competition arise from different locations. Children deficient in this skill, known as spatial listening, can struggle to understand speech even in relatively low levels of environmental noise.
A study by Tomlin et al that used the Listening in Spatialized Noise–Sentences (LiSN–S) test in a group of children with a history of otitis media found significant binaural speech perception deficits, even in participants assessed more than five years after the period of middle ear disease (Ear Hear; in press).
Furthermore, these authors found correlations with the age of onset and the duration of childhood otitis media, suggesting that there may be critical periods in the development of spatial processing when un-degraded auditory input is particularly important.
There is evidence that some forms of childhood binaural processing deficits may resolve in adolescence, after an extended period of consistent auditory input. However, this finding should not undermine the importance of early intervention, as hearing deficits in the early school years can result in communication, social, and academic problems, with the potential for lifelong impact.
Recent studies have shown that targeted remediation can improve the way the central auditory pathways process complex auditory signals, both in “normal” listeners ( Cereb Cortex 2012;22:1180-1190 http://cercor.oxfordjournals.org/content/22/5/1180.long) and in populations with auditory processing deficits ( Proc Natl Acad Sci U S A 2013;110:4357-4362 http://www.pnas.org/content/110/11/4357.long).
Song and colleagues, for example, demonstrated not only that figure–ground perception could be enhanced in a cohort of young adults, but also that the biological mechanisms underpinning this perception (measured in this case using speech-evoked auditory brainstem response) were malleable with short-term training ( Cereb Cortex 2012;22:1180-1190 http://cercor.oxfordjournals.org/content/22/5/1180.long).
In addition, spatial processing deficits were reversible in a series of experiments carried out by Cameron, Dillon, and colleagues ( J Am Acad Audiol 2011;22: 678-696 http://www.ncbi.nlm.nih.gov/pubmed/22212767; Audiol Res 2012;2:e15,86-93 http://www.audiologyresearch.org/index.php/audio/article/view/68).
A recent study by this group explored the use of the LiSN & Learn training program in a cohort of school-age Australian aboriginal children.
Prevalence and Remediation of Spatial Processing Disorder (SPD) in Indigenous Children in Regional Australia
Cameron S, Dillon H, Glyde H, Kanthan S, Kania A
Int J Audiol
This article describes findings from a pilot project in a remote, rural environment that aimed to identify and then treat spatial processing deficits. The authors did not specifically explore the middle ear histories of the participants but hypothesized that, since aboriginal children show the highest rate of middle ear disease of any population in the world ( Contemp Nurse 2003-2004;16[1-2]:145-150 http://www.contemporarynurse.com/archives/vol/16/issue/1-2/article/2049/middle-ear-problems-in-aboriginal-school-children), the authors would find a high prevalence of spatial deficits.
A total of 144 children age 6 to 12 were recruited and underwent initial audiometric evaluation. Of these children, 13 were excluded from the main study because of a significant hearing deficit (seven children) or intellectual disability (six children). The remaining participants underwent an evaluation of spatial listening ability using the LiSN-S test.
The Listening in Spatialized Noise–Sentences test measures the subject's capacity to segregate a target speech signal from competing speech noise. Test stimuli are presented via headphones, but a three-dimensional auditory environment is created by synthesizing the signals with head-related transfer functions ( J Am Acad Audiol 2008;19:377-391 http://www.ncbi.nlm.nih.gov/pubmed/19253811).
Speech reception threshold (the signal-to-noise ratio required to identify half of the words in target sentences [SRT]) is established in four conditions that vary in terms of the virtual location of the noise source (0° versus 90° azimuth) and the vocal quality of the speaker (same or different talker used to produce the target and background signals).
Age-related norms are available. An individual is considered to have a spatial processing disorder if the ability to use interaural spatial cues to localize the target speech—and, hence, obtain a release from the masking—is greater than 1.96 standard deviations below the mean.
Ten participants in this study (6.9% of the sample) were diagnosed in this way. This prevalence is considerably higher than expected for the general population and fits with the authors’ prediction that binaural processing deficits would be more common in young indigenous children.
Again, the authors did not report the middle-ear histories of the participants, but four of the children with spatial processing disorder had mild conductive hearing loss on the day of assessment, and the remaining children are likely to have experienced chronic middle ear disease at some point in the past.
Nine of the 10 children identified as having spatial processing disorder then undertook targeted auditory training using LiSN & Learn ( J Am Acad Audiol 2011;22:678-696 http://www.ncbi.nlm.nih.gov/pubmed/22212767).
This software-based program replicates a virtual reality auditory environment under headphones, as per the LiSN-S test, and requires that the subject identify words from a target sentence and select a matching image from a closed set displayed on a computer screen. Stimuli are presented in background noise using configurations that maximize reliance on spatial processing.
Previous work by Cameron et al demonstrated that LiSN & Learn can reverse spatial processing disorder ( J Am Acad Audiol 2011;22:678-696 http://www.ncbi.nlm.nih.gov/pubmed/22212767; Audiol Res 2012;2:e15,86-93 http://www.audiologyresearch.org/index.php/audio/article/view/68).
Under controlled circumstances, all reported cases have improved to normal levels on the post-training LiSN-S test, and decreases in speech reception threshold of around 10 dB have been typical.
Furthermore, real-life listening improvements, as reflected by child, parent, and teacher reports, have suggested that the beneficial effects are generalized beyond the training environment.
Unfortunately, one of the major findings of the current study was that implementation of auditory training in the field is more challenging than in the lab or clinic.
Even though the children were provided with rewards for participation, and the program was run in the school environment with teacher support, no child completed the entire program, and most children only finished around two-thirds of the training.
LiSN & Learn does employ a game format, but the tasks clearly failed to maintain the attention of the study population for the full 12-plus hours of focused listening over a 10-week period that was necessary to complete the program.
The findings suggest that either the training protocol needs to be modified (i.e., abbreviated), or activities with a sharper hook are required to capture and hold the interest of the current generation of computer game-savvy youngsters.
Not surprisingly, the children described in this study failed to show the spatial listening improvements described in previous LiSN & Learn experiments. Overall, there was no significant difference between pre- and post-training LiSN-S scores, although the participants’ teachers did report improvements in classroom listening over the course of training.
Interestingly, there was a correlation between the duration of participation and spatial listening improvement, indicating that those kids who stuck with the program for longer obtained the most benefit.
References on Tap
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