Volume 125, Issue 2, February 2009
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
125(2009); http://dx.doi.org/10.1121/1.3056564View Description Hide Description
The mean resonance frequency of the human middle ear under air conduction (AC) excitation is known to be around . However, studies suggest that the mean resonance frequency under bone conduction (BC) excitation is at a higher frequency around . To identify the cause for this difference, middle-ear responses to both AC and BC excitations were measured at the umbo and lateral process of the malleus using five human cadaver temporal bones. The resonance modes identified from these measurements, along with finite element analysis results, indicate the presence of two ossicular modes below . The dominant mode under AC excitation is the first mode, which typically occurs around and is characterized by a “hinging” ossicular motion, whereas the dominant mode under BC excitation is the second mode, which typically occurs around and is characterized by a “pivoting” ossicular motion. The results indicate that this second mode is responsible for the translational component in the malleus handle motion. The finding is also consistent with the hypothesis that a middle-ear structural resonance is responsible for the prominent peak seen at in BC limit data.
Postnatal development of sound pressure transformations by the head and pinnae of the cat: Monaural characteristics125(2009); http://dx.doi.org/10.1121/1.3058630View Description Hide Description
Although there have been many anatomical, physiological, and psychophysical studies of auditory development in cat, there have been no comparable studies of the development of the sound pressured transformations by the cat head and pinnae. Because the physical dimensions of the head and pinnae determine the spectral and temporal transformations of sound, as head and pinnae size increase during development, the magnitude and frequency ranges of these transformations are hypothesized to systematically change. This hypothesis was tested by measuring directional transfer functions (DTFs), the directional components of head-related transfer functions, and the linear dimensions of the head and pinnae in cats from the onset of hearing through adulthood. Head and pinnae dimensions increased by factors of and , respectively, reaching adult values by and , respectively. The development of the spectral notch cues to source location, the spatial- and frequency-dependent distributions of DTF amplitude gain (acoustic directionality), maximum gain, and the acoustic axis, and the resonance frequency and associated gain of the ear canal and concha were systematically related to the dimensions of the head and pinnae. These monaural acoustical properties of the head and pinnae in the cat are mature by 16 weeks.
125(2009); http://dx.doi.org/10.1121/1.3050304View Description Hide Description
Audiometric thresholds and otoacoustic emissions (OAEs) were measured in 285 U.S. Marine Corps recruits before and three weeks after exposure to impulse-noise sources from weapons’ fire and simulated artillery, and in 32 non-noise-exposed controls. At pre-test, audiometric thresholds for all ears were HL from and HL at . Ears with low-level or absent OAEs at pre-test were more likely to be classified with significant threshold shifts (STSs) at post-test. A subgroup of 60 noise-exposed volunteers with complete data sets for both ears showed significant decreases in OAE amplitude but no change in audiometric thresholds. STSs and significant emission shifts (SESs) between 2 and in individual ears were identified using criteria based on the standard error of measurement from the control group. There was essentially no association between the occurrence of STS and SES. There were more SESs than STSs, and the group of SES ears had more STS ears than the group of no-SES ears. The increased sensitivity of OAEs in comparison to audiometric thresholds was shown in all analyses, and low-level OAEs indicate an increased risk of future hearing loss by as much as ninefold.
125(2009); http://dx.doi.org/10.1121/1.3056566View Description Hide Description
Relationships between click-evoked otoacoustic emissions (CEOAEs) and behavioral thresholds have not been explored above due to limitations in CEOAE measurement procedures. New techniques were used to measure behavioral thresholds and CEOAEs up to . A long cylindrical tube of diameter, serving as a reflectionless termination, was used to calibrate audiometric stimuli and design a wideband CEOAE stimulus. A second click was presented above a probe click level that varied over a range, and a nonlinear residual procedure extracted a CEOAE from these click responses. In some subjects (age ) with normal hearing up to , CEOAE spectral energy and latency were measured up to . Audiometric thresholds were measured using an adaptive yes-no procedure. Comparison of CEOAE and behavioral thresholds suggested a clinical potential of using CEOAEs to screen for high-frequency hearing loss. CEOAE latencies determined from the peak of averaged, filtered temporal envelopes decreased to with increasing frequency up to . Individual CEOAE envelopes included both compressively growing longer-delay components consistent with a coherent-reflection source and linearly or expansively growing shorter-delay components consistent with a distortion source. Envelope delays of both components were approximately invariant with level.
A functional-magnetic-resonance-imaging investigation of cortical activation from moving vibrotactile stimuli on the fingertip125(2009); http://dx.doi.org/10.1121/1.3056399View Description Hide Description
Using a 100-element tactile stimulator on the fingertip during functional-magnetic-resonance imaging, brain areas were identified that were selectively activated by a moving vibrotactile stimulus (the sensation of a moving line being dragged over the fingertip). Activation patterns elicited by tactile motion, contrasted to an equivalent stationary stimulus, were compared in six human subjects with those generated by a moving visual stimulus, contrasted to an equivalent stationary stimulus. Results provide further evidence for a neuroanatomical convergence of tactile-motion processing and visual-motion processing in humans. The sites of this convergence are found to lie in the middle temporal complex , an area with known specialization for visual-motion processing, and in the intraparietal area of the posterior parietal cortex. In an advance on previous studies, the present study includes separate delineation of activations for moving tactile stimuli and activations for moving visual stimuli. Results suggest that the two sets of activations are not entirely collocated. Compared to the visual-motion activations, the tactile-motion activations are found to lie nearer the midline of the brain and further superior.