Perception of Small Frequency Differences in Children with Auditory Processing Disorder or Specific Language Impairment

Abstract

Background: Frequency discrimination is often impaired in children developing language atypically. However, findings in the detection of small frequency changes in these children are conflicting. Previous studies on children's auditory perceptual abilities usually involved establishing differential sensitivity thresholds in sample populations who were not tested for auditory deficits. To date, there are no data comparing suprathreshold frequency discrimination ability in children tested for both auditory processing and language skills.

Purpose: : This study examined the perception of small frequency differences (∆ƒ) in children with auditory processing disorder (APD) and/or specific language impairment (SLI). The aim was to determine whether children with APD and children with SLI showed differences in their behavioral responses to frequency changes. Results were expected to identify different degrees of impairment and shed some light on the auditory perceptual overlap between pediatric APD and SLI.

Research design: An experimental group design using a two-alternative forced-choice procedure was used to determine frequency discrimination ability for three magnitudes of ∆ƒ from the 1000-Hz base frequency.

Study sample: Thirty children between 10 years of age and 12 years, 11 months of age: 17 children with APD and/or SLI, and 13 typically developing (TD) peers participated. The clinical groups included four children with APD only, four children with SLI only, and nine children with both APD and SLI.

Data collection and analysis: Behavioral data collected using headphone delivery were analyzed using the sensitivity index d', calculated for three ∆ƒ was 2%, 5%, and 15% of the base frequency or 20, 50, and 150 Hz. Correlations between the dependent variable d' and the independent variables measuring auditory processing and language skills were also obtained. A stepwise regression analysis was then performed.

Results: TD children and children with APD and/or SLI differed in the detection of small-tone ∆ƒ. In addition, APD or SLI status affected behavioral results differently. Comparisons between auditory processing test scores or language test scores and the sensitivity index d' showed different strengths of correlation based on the magnitudes of the ∆ƒ. Auditory processing scores showed stronger correlation to the sensitivity index d' for the small ∆ƒ, while language scores showed stronger correlation to the sensitivity index d' for the large ∆ƒ.

Conclusion: Although children with APD and/or SLI have difficulty with behavioral frequency discrimination, this difficulty may stem from two different levels: a basic auditory level for children with APD and a higher language processing level for children with SLI; the frequency discrimination performance seemed to be affected by the labeling demands of the same versus different frequency discrimination task for the children with SLI.

Figure 1

R² change for the three magnitudes of Δf: small, medium, and large, when either the CELF (in blue) or the SCAN (in red) is added to the regression model.