Personal music systems and hearing.

OBJECTIVES: To measure the output sound pressure levels of personal music systems and evaluate their effect on hearing. METHODS: Output sound pressure levels at preferred volume settings and listening environment were measured using a manikin. Effects of personal music system use on hearing were evaluated using pure tone audiometry (in conventional and extended high frequency ranges), transient evoked otoacoustic emissions, syllable identification in noise, intensity discrimination, frequency discrimination and temporal modulation transfer function. RESULTS: Results showed, alarmingly, that large proportions of young adults are using personal music systems at levels higher than the safety limits set by regulatory bodies. Individuals who listened to personal music systems at levels higher than 80 dB LAeq exhibited poorer extended high frequency thresholds, reduced transient evoked otoacoustic emission amplitudes, poorer frequency discrimination, reduced modulation detection thresholds at 32 Hz modulation frequency, and reduced syllable identification in noise at -5 dB signal-to-noise ratio. Listening levels were significantly correlated with extended high frequency thresholds and transient evoked otoacoustic emission amplitudes. CONCLUSION: These results suggest that listening to music through personal music systems at higher volume levels may be hazardous to hearing.

Speech perception in individuals with auditory dys-synchrony: effect of lengthening of voice onset time and burst duration of speech segments.

OBJECTIVE: The purpose of this study was to evaluate the effect of lengthening of voice onset time and burst duration of selected speech stimuli on perception by individuals with auditory dys-synchrony. This is the second of a series of articles reporting the effect of signal enhancing strategies on speech perception by such individuals. METHODS: Two experiments were conducted: (1) assessment of the 'just-noticeable difference' for voice onset time and burst duration of speech sounds; and (2) assessment of speech identification scores when speech sounds were modified by lengthening the voice onset time and the burst duration in units of one just-noticeable difference, both in isolation and in combination with each other plus transition duration modification. RESULTS: Lengthening of voice onset time as well as burst duration improved perception of voicing. However, the effect of voice onset time modification was greater than that of burst duration modification. Although combined lengthening of voice onset time, burst duration and transition duration resulted in improved speech perception, the improvement was less than that due to lengthening of transition duration alone. CONCLUSION: These results suggest that innovative speech processing strategies that enhance temporal cues may benefit individuals with auditory dys-synchrony.

Speech perception in individuals with auditory dys-synchrony.

OBJECTIVE: This study aimed to evaluate the effect of lengthening the transition duration of selected speech segments upon the perception of those segments in individuals with auditory dys-synchrony. METHODS: Thirty individuals with auditory dys-synchrony participated in the study, along with 30 age-matched normal hearing listeners. Eight consonant-vowel syllables were used as auditory stimuli. Two experiments were conducted. Experiment one measured the 'just noticeable difference' time: the smallest prolongation of the speech sound transition duration which was noticeable by the subject. In experiment two, speech sounds were modified by lengthening the transition duration by multiples of the just noticeable difference time, and subjects' speech identification scores for the modified speech sounds were assessed. RESULTS: Subjects with auditory dys-synchrony demonstrated poor processing of temporal auditory information. Lengthening of speech sound transition duration improved these subjects' perception of both the placement and voicing features of the speech syllables used. CONCLUSION: These results suggest that innovative speech processing strategies which enhance temporal cues may benefit individuals with auditory dys-synchrony.