Auditory Discrimination Using Frequency-Modulated Amplification with Long-Term Amplitude Compression.
Bernard David Shea · Scholarworks (University of Massachusetts Amherst) · 1994
This dissertation considers the effects of long-term amplitude compression used in narrow-band frequency modulated (FM) assistive listening devices on the auditory discrimination of severely and profoundly hearing-impaired individuals. Compression has been used in narrow-band FM transmitters for hearing-impaired children in educational programs for over twenty years. It restricts the peak deviation of the FM signal to within allowable limits. Narrow-band FM equipment can vary in peak limitation approaches via compression, i.e., using a form of compression limiting or using long-term compression (automatic volume control). Numerous investigations have studied the benefits of FM system use, but none have tested the benefits or deleterious effects of these compression forms on the auditory discrimination of hearing-impaired individuals. Despite the marked limitations associated with severe or profound sensorineural hearing impairment in children, spoken language development is possible. Research and experience have suggested that the auditory system represents the best sensory input channel for these children. With appropriate amplification and educational intervention they can achieve dramatic improvements in speech perception, speech production, language development, and educational achievement (Boothroyd, 1985; Hudgins, 1953, 1954; Ling & Milne, 1981; Wedenberg, 1954). Most hearing-impaired children in educational programs across the United States receive the amplified teacher's speech signal via narrow-band frequency modulated (FM) transmission, yet a controlled investigation of the input compression used in these systems has never been conducted. This dissertation reviews and discusses narrow-band frequency modulated (FM) radio wave systems and the use of audio compression. The experiment tested 32 students with severe to profound sensorineural hearing loss under two narrow-band FM transmitter conditions. The FM transmitter conditions were varied on the basis of long-term compression activation points, i.e., 75 dB versus 90 dB. The students' perception of one supra-segmental and eight segmental contrasts were examined using a three-interval, forced-choice paradigm. This procedure measured the students' access to phonologically significant cues. Analyses of the speech perception scores across the two conditions suggested that the use of long-term amplitude compression is advantageous for this population.