Volume 120, Issue 2, August 2006
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
120(2006); http://dx.doi.org/10.1121/1.2211407View Description Hide Description
This study investigated noise-induced changes in suppression growth (SG) of distortion product otoacoustic emissions (DPOAEs). Detailed measurements of SG were obtained in rabbits as a function of frequencies at four primary-tone levels. SG measures were produced by using suppressor tones (STs) presented at two fixed distances from . The magnitude of suppression was calculated for each ST level and depicted as contour plots showing the amount of suppression as a function of the frequency. At each , SG indices included slope, suppression threshold, and an estimate of the tip-to-tail value. All suppression measures were obtained before and after producing a cochlear dysfunction using a monaural exposure to a , SPL octave-band noise centered at . The noise exposure produced varying amounts of cochlear damage as revealed by changes in DP-grams and auditory brainstem responses. However, average measures of SG slopes, suppression thresholds, and tip-to-tail values failed to mirror the mean DP-gram loss patterns. When suppression-based parameters were correlated with the amount of DPOAE loss, small but significant correlations were observed for some measures. Overall, the findings suggest that measures derived from DPOAE SG are limited in their ability to detect noise-induced cochlear damage.
Use of stimulus-frequency otoacoustic emission latency and level to investigate cochlear mechanics in human earsa)120(2006); http://dx.doi.org/10.1121/1.2214147View Description Hide Description
Stimulus frequency otoacoustic emission (SFOAE) sound pressure level (SPL) and latency were measured at probe frequencies from 500 to and probe levels from 40 to SPL in 16 normal-hearing adult ears. The main goal was to use SFOAE latency estimates to better understand possible source mechanisms such as linear coherent reflection, nonlinear distortion, and reverse transmission via the cochlear fluid, and how those sources might change as a function of stimulus level. Another goal was to use SFOAE latencies to noninvasively estimate cochlear tuning. SFOAEs were dominated by the reflection source at low stimulus levels, consistent with previous research, but neither nonlinear distortion nor fluid compression become the dominant source even at the highest stimulus level. At each stimulus level, the SFOAE latency was an approximately constant number of periods from 1000 to , consistent with cochlear scaling symmetry. SFOAE latency decreased with increasing stimulus level in an approximately frequency-independent manner. Tuning estimates were constant above , consistent with simultaneous masking data, but in contrast to previous estimates from SFOAEs.
Effects of hearing loss and spectral shaping on identification and neural response patterns of stop-consonant stimuli120(2006); http://dx.doi.org/10.1121/1.2204588View Description Hide Description
In order to determine the effects of hearing loss and spectral shaping on a dynamic spectral speech cue, behavioral identification and neural response patterns of stop-consonant stimuli varying along the /b-d-g/ place-of-articulation continuum were measured from 11 young adults (mean age=27 years) and 10 older adults (mean age=55.2 years) with normal hearing, and compared to those from 10 older adults (mean age=61.3 years) with mild-to-moderate hearing impairment. Psychometric functions and N1-P2 cortical evoked responses were obtained using consonant-vowel (CV) stimuli with frequency-independent (unshaped) amplification as well as with frequency-dependent (shaped) amplification that enhanced relative to the rest of the stimulus. Results indicated that behavioral identification and neural response patterns of stop-consonant CVs were affected primarily by aging and secondarily by age-related hearing loss. Further, enhancing the audibility of the transition cue with spectrally shaped amplification partially reduced the effects of age-related hearing loss on categorization ability but not neural response patterns of stop-consonant CVs. These findings suggest that aging affects excitatory and inhibitory processes and may contribute to the perceptual differences of dynamic spectral cues seen in older versus young adults. Additionally, age and age-related hearing loss may have separate influences on neural function.
120(2006); http://dx.doi.org/10.1121/1.2217567View Description Hide Description
This study was designed to characterize the effect of background noise on the identification of syllables using behavioral and electrophysiological measures. Twenty normal-hearing adults performed an identification task in a two-alternative forced-choice paradigm. Stimuli consisted of naturally produced syllables /da/ and /ga/ embedded in white noise. The noise was initiated before the onset of the speech stimuli in order to separate the auditory event related potentials (AERP) response to noise onset from that to the speech. Syllables were presented in quiet and in five SNRs: , , 0, , and . Results show that (1) performance accuracy, , and reaction time were affected by the noise, more so for reaction time; (2) both N1 and P3 latency were prolonged as noise levels increased, more so for P3; (3) /ga/ was better identified than /da/, in all noise conditions; and (4) P3 latency was longer for /da/ than for /ga/ for SNR 0 through , while N1 latency was longer for /ga/ than for /da/ in most listening conditions. In conclusion, the unique stimuli structure utilized in this study demonstrated the effects of noise on speech recognition at both the physical and the perceptual processing levels.