Development of an adaptive low-pass filtered speech test for the identification of auditory processing disorders

One type of test commonly used to examine auditory processing disorders (APD) is the low-pass filtered speech test (LPFST), of which there are various versions. In LPFSTs, a monaural, low-redundancy speech sample is distorted by using filtering to modify its frequency content. Due to the richness of the neural pathways in the auditory system and the redundancy of acoustic information in spoken language, a normal listener is able to recognize speech even when parts of the signal are missing, whereas this ability is often impaired in listeners with APD. One limitation of the various versions of the LPFST is that they are carried out using a constant level of low-pass filtering (e.g. a fixed 1kHz corner frequency) which makes them prone to ceiling and floor effects. The purpose of this study was to counter these effects by modifying the LPFST using a computer-based adaptive procedure, and to evaluate the performance of normal-hearing participants of varying ages on the test.

In this preliminary study, 33 adults and 30 children (aged 8-11 years) with no known history of listening difficulties were tested. The University of Canterbury Adaptive Speech Test (UCAST) platform was used to administer a four-alternative forced-choice adaptive test that altered a low-pass filter (LPF) to track the corner frequency at which participants correctly identified a certain percentage of the word stimuli.

Findings on the University of Canterbury Adaptive Speech Test-Filtered Words (UCAST-FW) indicated a significant maturational effect. Adult participants performed significantly better on the UCAST-FW in comparison to the child participants. The UCAST-FW test was reliable over repeated administrations.

An adaptive low-pass filtered speech test such as the UCAST-FW is sensitive to maturational changes in auditory processing ability.