Are "Dichotic" Deficits Uniquely Dichotic? Investigating Dichotic Performance with the Dichotic Digits Difference Test (DDdT) in a Large Clinical Population of Children Referred for an Auditory Processing Assessment

Background: Previous studies in a large population of typically developing (TD) children and a small clinical group showed high correlations between the dichotic and diotic conditions of the Dichotic Digits difference Test (DDdT), as well as between DDdT performance and measures of memory and attention. Purpose: The purpose of the study was to investigate the performance on the DDdT in a large clinical sample. Research Design: Correlational analysis between the DDdT diotic condition and the dichotic free recall (FR) right-ear, left-ear, and total (ear-averaged) conditions, as well as between DDdT and memory performance. Study Sample: One hundred one children (6 years 3 months to 15 years 0 month, mean 9 years 6 months) were referred for assessment to the Australian Hearing Central Auditory Processing Disorder (CAPD) service. Results were compared with data from 112 TD children collected from previously published studies. Data Collection and Analysis: Z-scores were used to account for the effect of age on performance. Mean differences between clinical and TD children were investigated using analysis of variance (ANOVA). Pearson product-moment correlations determined the strength of relationships between DDdT conditions and the number memory forward (NMF) and reversed (NMR) subtests of the Test of Auditory Processing Skills-Third Edition. Results: Performance by the clinical group on the DDdT dichotic FR (RE, LE, and total) conditions was significantly correlated with the diotic condition (r = 0.7; 0.7, 0.8; p < 0.001). Significant correlations were found between the DDdT diotic and dichotic FR conditions and the NMF (r = 0.5-0.6, p < 0.001) and NMR (r = 0.2-0.5, p < 0.025-0.001). ANOVA revealed no significant difference between the TD and clinical groups (p = 1.0000) in respect to the advantage they got from dichotic listening (calculated as dichotic FR total minus diotic score). Multiple regression revealed that diotic performance and short-term memory accounted for 68% of the variation in dichotic performance. Random measurement error accounted for a further 16%. Conclusions: Factors other than dichotic performance strongly impact a child's ability to perform a dichotic digit listening task. This result has widespread implications in respect to the interpretation of CAPD test results.