Dichotic Digits Test Performance Across the Ages: Results From Two Large Epidemiologic Cohort Studies
Authors: Fischer Mary E. , Cruickshanks Karen J. , Nondahl David M. , Klein Barbara E. K. , Klein Ronald , Pankow James S. , Tweed Ted S. , Dalton Dayna S. , Paulsen Adam J. 
Published: December 2016

Objectives:
The Dichotic Digits test (DDT) has been widely used to assess central auditory processing but there is limited information on observed DDT performance in a general population. The purpose of the study was to determine factors related to DDT performance in a large cohort spanning the adult age range.

Design:
The study was cross-sectional and subjects were participants in the Epidemiology of Hearing Loss Study (EHLS), a population-based investigation of age-related hearing loss, or the Beaver Dam Offspring Study (BOSS), a study of aging in the adult offspring of the EHLS members. Subjects seen during the 4th EHLS (2008 to 2010) or the 2nd BOSS (2010 to 2013) examination were included (N = 3655 participants [1391 EHLS, 2264 BOSS]; mean age = 61.1 years, range = 21 to 100 years). The free and right ear-directed recall DDTs were administered using 25 sets of triple-digit pairs with a 70 dB HL presentation level. Pure-tone audiometric testing was conducted and the pure-tone threshold average (PTA) at 0.5, 1, 2, and 4 kHz was categorized using the worse ear: no loss = PTA ≤ 25 dB HL; mild loss = 25 < PTA ≤ 40 dB HL; moderate or marked loss = PTA > 40 dB HL. Cognitive impairment was defined as a Mini-Mental State Examination score < 24 (maximum = 30) or a self- or proxy-reported history of dementia or Alzheimer’s disease. Demographic information was self-reported. General linear models were fit and multiple linear regression was performed.

Results:
The mean total free recall DDT score was 76.7% (range = 21.3 to 100%). Less than 10% of the participants had a total free recall score below 60% correct. The mean right ear-directed recall score was 98.4% with 69% of the participants scoring 100% and another 15.5% scoring 98.7% (1 incorrect digit). In multivariable modeling of the total free recall scores, the predicted mean free recall score was 1 percentage point lower for every 5-year increase in age, 2.3 percentage points lower in males than females, 8.7 percentage points lower in participants with less than a high school degree than in those with college degrees, 6.8 percentage points lower in participants with a moderate or marked hearing loss compared with no hearing loss, and 8.3 percentage points lower in participants with cognitive impairment compared with those without cognitive impairment. These 5 factors were independently and significantly related to performance and accounted for 22.7% of the total variability in free recall scores.

Conclusions:
Substantial variation in the total free recall DDT scores but very little variation in the right ear-directed recall DDT scores was observed. Age, sex, education, hearing loss severity, and cognitive impairment were found to be significantly related to DDT scores but explained less than 25% of the total variability in total free recall scores. The right ear-directed recall DDT by itself may not be of benefit in assessing central auditory processing in a general population because of its limited variability but further evaluation of factors potentially related to free recall DDT variability may prove useful.