LM405 - When Two Ears Are Not Better Than One: Dichotic Deficits in Children

Abstract:
Poor dichotic test results have long been linked to listening, learning, language and reading problems despite normal hearing acuity and dissatisfaction with binaural amplification in persons with hearing loss. New methods to evaluate dichotic performance have revealed a high prevalence of severe deficits among children clinically assessed for APD, the general school-age population, and adjudicated adolescents. Two distinct deficit patterns can be identified and remediated with an auditory training protocol. Evidence supports an alternative clinical approach, using dichotic testing to triage auditory processing disorders in all patients and to screen all schoolchildren for unidentified dichotic listening weaknesses.

Summary:
Audiologists see many individuals with normal hearing acuity or with binaural amplification devices for hearing loss who demonstrate difficulties in listening, language, learning, and reading that may stem from a dichotic listening deficit. Efficient, evidence-based methods in the audiology clinic to identify a dichotic deficit and provide treatment to remediate it could have a positive impact on communication-based outcomes in patients of all ages. Most audiologists should consider a dichotic listening assessment as part of standard, routine clinical care.

Dichotic tests are used to identify a deficit in binaural integration, the ability to accurately process information arriving at the two ear simultaneously. Amblyaudia is characterized by normal performance in the dominant ear and poorer than normal performance in the non-dominant ear that yields a larger than normal asymmetry. Dichotic dysaudia is characterized by poor performance in both ears with a normal asymmetry between them.

Because scores from dichotic tests are skewed from a maximum of 100% in a one-tail distribution, the use of standard deviation values to characterize deficits has underestimated their prevalence. Percentile ranks, developed through non-parametric statistical bootstrapping methods, have produced new values to interpret scores from two dichotic tests (Moncrieff, 2024). Cut-off values representing the 5^th, 10^th and 25^th percentiles of performance are available from age 5 to 79 for the Randomized Dichotic Digits Test (RDDT) (Strouse & Wilson, 1999; Moncrieff & Wilson, 2009) and from age 5 to 18 for the Dichotic Words Test (DWT) (Moncrieff, 2015).

A dichotic deficit is identified only when a listener’s ear scores produce a matched performance pattern from these two tests. The severity of the deficit can also be characterized by ranking score values that fall below the 5^th, 10^th and 25^th percentiles for a person the same age. Because it takes only 10-15 minutes to identify a deficit and rank its severity with these tests and reimbursement is available for the time spent, most clinicians can incorporate dichotic assessment into their practices. Conventional reports estimated a very low prevalence of auditory processing disorders in children, but significantly higher rates of severe dichotic deficits with scores below the 5th percentile have been demonstrated with this alternative method of assessment. Evidence of severe deficits in children with normal hearing acuity tested in an audiology clinic, at school, or at a juvenile detention center and in children with cochlear implants and/or hearing aids in an option school will be discussed.

Old and new theories regarding the neurophysiologic mechanisms involved in dichotic listening that reveal risk factors for a severe deficit will be compared and evidence from electrophysiologic responses will be discussed. Details of other behavioral deficits that may co-occur, together with underlying theories related to contribution from bottom-up versus top-down processes will also be discussed.

Brief Summary of Clinical Takeaways:
The clinical takeaway from this session is that audiologists can efficiently identify dichotic listening deficits in all patients ages 5 and older and use information about dichotic skills to more effectively manage clinical care, communication outcomes, and patient satisfaction.