Auditory signal processing in a hearing-impaired subject with residual ultra-audiometric hearing

A number of hearing-impaired individuals with near-normal thresholds for frequencies above 8,000 Hz who are characterized by good speech articulation have recently been identified. It is unclear whether this unusually good articulation is linked to the ability of such persons to process speech signals containing energy that falls within the range of their residual, high-frequency hearing (for example, certain consonants). This paper reports a detailed study of the signal-processing capabilities of one patient with a long-standing, severe to profound hearing loss in the standard audiometric range, and normal left-ear thresholds in the region of 13,000 Hz. Measures obtained include difference limens for frequency and intensity, gap detection, rate matching, temporal integration, and tone-on-tone masking profiles (psychoacoustical tuning curves). In addition, measures of speech production and perception were made when the patient was using an experimental hearing aid designed to transpose speech range frequencies into the region of her residual high-frequency hearing. Results indicate the patient can efficiently process signals which fall within the band of her best hearing, and suggest her ultra-audiometric hearing may be useful in speech communication.