Spatial processing disorder (SPD) is a type of APD caused by deficits related to spatial processing skills. More specifically, this deficit would involve a phenomenon known as spatial release from masking (SRM) (Cameron & Dillon, 2008). In simple words, SRM is the improvement of speech intelligibility when the target speech and the background noise are spatially separated (Litovsky, 2005; Best et al., 2012; Misurelli and Litovsky, 2015).
E.g., if you are in a noisy pub (or your child is in a noisy classroom), you can hear multiple sound sources probably coming from different directions. To successfully segregate and differentiate them, you should be able to use 'spatial cues' that will improve your “speech in noise skill” in those situations. This expected improvement is known as the SRM, and it can be measured clinically. Individuals with SPD present a “small” SRM, as they are not able to use those "spatial cues" effectively. As a consequence, they can struggle to understand the target speech even when it is spatially separated from the background noise. This type of deficit is clinically assessed by comparing performance in two different scenarios: the first one, in which target speech and background noise are at the same location, and the second, when they are separated. The result should reflect how the individual benefits from spatial cues; the higher the difference between performance in both scenarios, the better.
Research has shown that in some children with listening difficulties, SRM is atypically small, especially in children with a history of otitis media with effusion (Tomlin and Rance, 2014; Graydon et al., 2017). The explanation is related to the auditory deprivation experienced by those children during a critical developmental period. More specifically, the fluctuating nature of their hearing loss leads to inconsistent auditory signals arriving at the brain and hence affecting the development of listening skills, such as spatial processing skills (Graydon et al, 2017). As the main SPD symptom, those children would experience difficulty understanding and focusing on a specific auditory stimulus in the presence of background noise.
The assessment of spatial processing skills should be part of any auditory processing evaluation so the SPD can be differentiated from a general APD, and adequately treated. LiSN-S is one of the clinical tests to assess spatial processing skills.
In the following paper, myself and colleagues investigated the performance of British children on the LiSN-S, to facilitate the use of this test in the UK. Click on the link to have access to the journal.
Murphy CFB, Hashim E, Dillon H, Bamiou DE.
Int J Audiol. 2019 Nov;58(11):754-760.
References:
Cameron, S., and H. Dillon. 2008. The Listening in Spatialized Noise-Sentences Test (LISN-S): Comparison to the Prototype LISN and Results from Children with Either a Suspected (Central) Auditory Processing Disorder or a Confirmed Language Disorder. Journal of the American Academy of Audiology 19(5): 377–391.
Litovsky, R. J. 2005. Speech Intelligibility and Spatial Release from Masking in Young Children. The Journal of the Acoustical Society of America 117(5): 3091–3099.
Best, V., N. Marrone, C. R. Mason, and G. Jr. Kidd. 2012. The Influence of Non-Spatial Factors on Measures of Spatial Release From Masking. Journal of the Acoustical Society of America 131(4): 3103–3110.
Misurelli, S. M., and R. Y. Litovsky. 2015. “Spatial Release from Masking in Children with Bilateral Cochlear Implant and with Normal Hearing: Effect of Target-Interferer Similarity.” Journal of the Acoustical Society of America 138(1): 319–331.
Tomlin, D., and G. Rance. 2014. “Long-Term Hearing Deficits after Childhood Middle Ear Disease.” Ear and Hearing 35(6): e233–42.
Graydon, K., G. Rance, R. Dowell, and B. Van Dun. 2017. “Consequences of Early Conductive Hearing Loss on Long-Term Binaural Processing.” Ear and Hearing 38(5): 621–627.