Volume 128, Issue 2, August 2010
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
128(2010); http://dx.doi.org/10.1121/1.3458855View Description Hide Description
The relationship between the bone conduction (BC) part and the air conduction (AC) part of one’s own voice has previously not been well determined. This relation is important for hearing impaired subjects as a hearing aid affects these two parts differently and thereby changes the perception of one’s own voice. A large ear-muff that minimized the occlusion effect while still attenuating AC sound was designed. During vocalization and wearing the ear muff the ear-canal sound pressure could be related to the BC component of a person’s own voice while the AC component was derived from the sound pressure at the entrance of an open ear-canal. The BC relative to AC sensitivity of one’s own voice was defined as the ratio between these two components related to the ear-canal sound pressure at hearing thresholds for BC and AC stimulation. The results of ten phonemes showed that the BC part of one’s own voice dominated at frequencies between 1 and 2 kHz for most of the phonemes. The different phonemes gave slightly different results caused by differences during vocalization. However, similarities were seen for phonemes with comparable vocalization.
Subjective quantification of earplug occlusion effect using external acoustical excitation of the mouth cavity128(2010); http://dx.doi.org/10.1121/1.3458843View Description Hide Description
Occlusion of the ear canal by hearing aids or hearing protectors often results in an occlusion effect, which creates a discomfort to wearers in that it changes their perception of their own voice. As no account was found in the literature on the quantification of this subjective voice occlusion effect, an experimental method is proposed based on the use of an artificial sound source emitting within the subject’s mouth to replace his own voice. A block diagram is constructed to identify the different internal sound path components involved in the perception of one’s own voice and is used to show that the subjective voice occlusion effect is the weighted energy summation of two components. The first component, the voice air and body conduction occlusion effect for which data is obtained from the experiments reported in the present paper, constitute the lower limit of the subjective voice occlusion effect. The second component, the voice body conduction occlusion effect for which data is available in the literature, constitutes the upper limit. From these limits, order of magnitudes for subjective voice occlusion effect intervals are estimated to be below 2000 Hz and above 2000 Hz.
On- and off-frequency compression estimated using a new version of the additivity of forward masking technique128(2010); http://dx.doi.org/10.1121/1.3455844View Description Hide Description
On- and off-frequency compression at the 4000- and 8000-Hz cochlear places were estimated using a new version of the additivity of forward masking (AFM) technique, that measures the effects of combining two non-overlapping forward maskers. Instead of measuring signal thresholds to estimate compression of the signal as in the original AFM technique, the decrease in masker threshold in the combined-masker condition compared to the individual-masker conditions is used to estimate compression of the masker at the signal place. By varying masker frequency it is possible to estimate off-frequency compression. The maskers were 500-Hz-wide bands of noise, and the signal was a brief pure tone. Compression at different levels was estimated using different overall signal levels, or different masker-signal intervals. It was shown that the new AFM technique and the original AFM technique produce consistent results. Considerable compression was observed for maskers well below the signal frequency, suggesting that the assumption of off-frequency linearity used in other techniques may not be valid. Reducing the duration of the first masker from 200 to 20 ms reduced the compression exponent in some cases, suggesting a possible influence of olivocochlear efferent activity.
128(2010); http://dx.doi.org/10.1121/1.3458813View Description Hide Description
Although lizards have highly sensitive ears, it is difficult to condition them to sound, making standard psychophysical assays of hearing sensitivity impractical. This paper describes non-invasive measurements of the auditory brainstem response (ABR) in both Tokay geckos (Gekko gecko; nocturnal animals, known for their loud vocalizations) and the green anole (Anolis carolinensis, diurnal, non-vocal animals). Hearing sensitivity was measured in 5 geckos and 7 anoles. The lizards were sedated with isoflurane, and ABRs were measured at levels of 1 and 3% isoflurane. The typical ABR waveform in response to click stimulation showed one prominent and several smaller peaks occurring within 10 ms of the stimulus onset. ABRs to brief tone bursts revealed that geckos and anoles were most sensitive between 1.6–2 kHz and had similar hearing sensitivity up to about 5 kHz (thresholds typically 20–50 dB SPL). Above 5 kHz, however, anoles were more than 20 dB more sensitive than geckos and showed a wider range of sensitivity (1–7 kHz). Generally, thresholds from ABR audiograms were comparable to those of small birds. Best hearing sensitivity, however, extended over a larger frequency range in lizards than in most bird species.