Diagnosis of Auditory Processing Disorder in Children using an Adaptive Filtered Speech Test

Auditory Processing Disorder (APD) is an auditory-specific perceptual deficit in the processing of auditory stimuli that occurs in spite of normal peripheral hearing thresholds and normal intellectual capacity American Speech-Language-Hearing Association (ASHA, 2005). The diagnostic process of APD typically involves a test battery consisting of sub-tests designed to examine the integrity of various auditory processes of the central auditory nervous system (CANS). One category of these sub-tests is the low-pass filtered speech test (FST), whereby a speech signal is distorted by using filtering to modify its frequency content. One limitation of the various versions of the FST currently available is that they are administered using a constant level of low-pass filtering (e.g. a fixed 1 kHz corner frequency) which makes them prone to ceiling and floor effects (Farrer & Keith, 1981). As a consequence, the efficacy and accuracy of these tests is significantly compromised (Martin & Clark, 1977). The purpose of the present study was to counter these effects by utilising the University of Canterbury Adaptive Filtered Speech Test (UCAST) which uses a computer-based adaptive procedure intended to improve the efficiency and sensitivity of the test over its constant-level counterparts. A comprehensive APD test battery was carried out on 18 children aged 7-13 suspected of APD and on an aged-matched control group of 10 children. Fifteen of the APD suspected children were diagnosed with APD based on their performance on a traditional APD test battery, comprising the Compressed and Reverberated Words Test (CRWT), the Double Digits test (DDT), the Frequency Pattern test (FPT) and the Random Gap Detection test (RGDT). In addition, the UCAST was administered to examine whether the low-pass filter limit at which children score 62.5% of words correct i) differed significantly between children who either passed or failed the APD test battery; ii) correlated with their score on the traditional APD battery (TAPDB); and iii) correlated with their score on a commercially available low-pass filtered speech test, the Filtered Words Subtest of SCAN-C (Keith, 2000b). Results demonstrated a significant difference between the UCAST low-pass filter limit at which APD and control children scored 62.5% words correct (two-way repeated measures ANOVA, p 0.05). These findings provide evidence that an adaptive filtered speech test may discriminate between children with and without APD with greater sensitivity and specificity than its constant-level counterparts