Through adopting language-dependent modifications, caregivers and professionals should have a more adequate tool to monitor children's auditory access to the full range of Mandarin speech sounds.

In contrast with previous research focusing on cochlear implants, this study examined the speech performance of hearing aid users with conductive (n = 11), mixed (n = 10), and sensorineural hearing loss (n = 7) and compared it with the speech of hearing control. Speech intelligibility was evaluated by computing the vowel space area defined by the Mandarin Chinese corner vowels /a, u, i/. The acoustic differences between the vowels were assessed using the Euclidean distance. The results revealed that both the conductive and mixed hearing loss groups exhibited a reduced vowel working space, but no significant difference was found between the sensorineural hearing loss and normal hearing groups. An analysis using the Euclidean distance further showed that the compression of vowel space area in conductive hearing loss can be attributed to the substantial lowering of the second formant of /i/. The differences in vowel production between groups are discussed in terms of the occlusion effect and the signal transmission media of various hearing devices.

The results confirm the validity of the Chinese Sound Test, indicating that the testing sounds can be reliably used to assess the perception of frequency-specific information. Crucially, these data also demonstrate that the Chinese Sound Test is a useful tool to identify red flags of poor auditory access in daily environment to monitor device malfunctions and possible hearing fluctuations.

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