Hans Kunov

Noise exposure of music teachers.

A noise exposure survey was performed to assess the risk of hearing loss to school music teachers during the course of their activities. Noise exposure of 18 teachers from 15 schools was measured using noise dosimeters. The equivalent continuous noise level (Leq) of each teacher was recorded during single activities (classes) as well as for the entire day, and a normalized 8-hour exposure, termed the noise exposure level (Lex) was also computed. The measured Leq exceeded the 85-dBA limit for 78% of the teachers. Lex exceeded 85 dBA for 39% of the teachers. Limited recommendations on how to reduce the noise exposures are provided. The need for a hearing conservation program has also been emphasized.

Recording human evoked potentials that follow the pitch contour of a natural vowel

We investigated whether pitch-synchronous neural activity could be recorded in humans, with a natural vowel and a vowel in which the fundamental frequency was suppressed. Small variations of speech periodicity were detected in the evoked responses using a fine structure spectrograph (FSS). A significant response (P/spl Lt/0.001) was measured in all seven normal subjects even when the fundamental frequency was suppressed, and it very accurately tracked the acoustic pitch contour (normalized mean absolute error <0.57%). Small variations in speech periodicity, which humans can detect, are therefore available to the perceptual system as pitch-synchronous neural firing. These findings suggest that the measurement of pitch-evoked responses may be a viable tool for objective speech audiometry.

Effects of rise/decay time on the lateralization of interaurally delayed 1-kHz tones.

Experiments in lateralization were performed to evaluate the relative contribution of onset and phase cues in binaural hearing. A 1-kHz signal was presented with interaural stimulus delays ranging from 0 to 1000 microseconds, corresponding to phase shifts of 0 degree to 360 degrees. For a given value of delay, the leading signal was presented randomly to the right or left ear over a block of 100 trials, and the laterality of the resultant image was judged. The percentage of correct judgments was plotted as a function of delay with rise/decay time as a parameter. Values of rise/decay time ranged from 0 to 500 ms. The results indicated that rise/decay times of at least 200 ms are necessary to avoid contributions from the onset cue to the formation of lateralization judgments. For rise/decay times shorter than 200 ms, a conflict occurs between phase and onset cues in the region of phase shifts from 180 degrees to 360 degrees. At the limit with very short rise/decay times, the onset cue completely overrides the phase cue.

Distortion product otoacoustic emissions stimulated through bone conduction.

Objective: To demonstrate the viability of bone conduction as a novel method for stimulation of distortion product otoacoustic emissions (DPOAEs). Design: DPOAEs were recorded from a single ear of 23 normally hearing adults using bone and air conduction for the delivery of stimulus tones. Exploration of the input‐output function was performed by varying stimulus frequency and magnitude. Results: Bone‐stimulated emissions demonstrated similar characteristics to those obtained through standard air transmission techniques. Characteristic nonlinear DPOAE growth was found as the magnitude of the higher frequency stimulus tone, L2, was increased monotonically with other parameters fixed. Bilateral stimulation due to using bone conduction did not saturate the mechanisms of emission suppression. Emission magnitude was not altered substantially by occlusion of the ear canal. Conclusion: Bone conduction can be used successfully to elicit DPOAEs. Absolute comparison of air‐ and bone‐stimulated DPOAEs was difficult because of imprecise calibration of the bone conductors for each individual and particular placement. Properties unique to bone conduction, such as simultaneous bilateral stimulation and reduction of stimulus magnitude in the ear canal, may make bone conduction attractive for clinical measurement of DPOAEs.

Cochlear response audiometer

The invention provides a cochlear response audiometer, and new methods for signal generation, detection and processing. The invention preferably uses bone conducted sound, applied to the mastoid, forehead, or any other place with good mechanical contact to the skull, via a vibrator. The bone conducted sound stimulates the cochlea via the skull. The stimulus also produces a sound in the ear canal, but at a very low level, so there is no high level stimulus signal and ringing travelling toward the cochlea at the same time as the cochlear response is travelling back into the ear canal. The responses from the cochlea are recorded, preferably by using a differential amplifier input circuit for the microphone when air-borne response signals are used, and the responses are processed in a way which compensates for the stimulus artefact, by subtracting a scaled-down version of the cochlear response to a large stimulus from the cochlear response to a moderate stimulus.

Lateralization based on interaural phase differences: Effects of frequency, amplitude, duration, and shape of rise/decay

Experiments in lateralization were performed to evaluate the relative contribution of envelope and phase cues in binaural hearing with particular reference to the effects of frequency, amplitude, shape of rise/decay, and duration of peak amplitude. Pure-tone signals were presented with interaural phase shifts ranging between 90 degrees and 360 degrees. For a given value of phase shift, the leading signal was presented randomly to the right or left ear over a block of 100 trials, and the laterality of the resultant image was judged. Rise/decay time was varied from 5 to 200 ms across blocks. The results confirmed our previous finding that a rise/decay time of at least 200 ms is required to secure a psychophysically steady-state signal. This value will, however, depend on the values chosen for the other signal parameters. Within limits, decreasing intensity could be compensated for by decreasing rise/decay, suggesting the psychophysical importance of the initial segment of the signal (precedence effect). For low frequencies of 650 to 1250 Hz, performance is sensitive to interaural phase shift and largely independent of frequency. For higher frequencies of 1500 and 2000 Hz, lateralization is independent of the phase cue and also largely insensitive to change in rise/decay time. Finally, performance remains unchanged with variation in peak duration ranging from 25 to 200 ms.

Suppression of distortion product otoacoustic emissions and hearing threshold.

A distortion product otoacoustic emission (DPOAE) suppression tuning curve (STC) shows the minimum level of suppressor tone that is required to reduce DPOAE level by a fixed amount, as a function of suppressor frequency. Several years ago, Mills [J. Acoust. Soc. Am. 103, 507-523 (1998)] derived, theoretically, an approximately linear relationship between the tip-to-tail suppressor level difference on a DPOAE STC, and the gain of the cochlear amplifier, defined as the maximum increase in the active over the passive basilar membrane (BM) response. In this paper, preliminary data from adult human subjects are presented that establish a correlation between this tip-to-tail DPOAE STC difference and the threshold of hearing, the latter measured at the frequency of the f2 primary tone. Assuming that both suppression and the DPOAE are by-products of active, nonlinear BM dynamics, the above result suggests that threshold elevation in mild levels of hearing loss may be attributed, in part, to a reduction of cochlear amplifier gain, which is detectable with the suppression paradigm.

Peripheral vision lipreading aid

A pair of eyeglasses with a commercially available two-dimensional red LED array (5*7), and its associated electronics was developed. The display is visible only to the wearer, and is located in the temporal field and the horizontal meridian of the right eye. Selected speech features were encoded as visual patterns for presentation to the lipreader. These features of the speech signal (the fundamental frequency of the speech, high-frequency energy, and low-passed speech signal or total energy envelope) were presented with the objective of providing information about voicing and plosion/frication. Experiments demonstrate the capability of the peripheral display in conveying speech information. Presenting vowel-consonant-vowel syllables, the performance was in excess of 76% with aided lipreading as compared to 41% by lipreading only.<<ETX>>

A Strategic Information System to Facilitate the Use of Performance Indicators in Hospitals

Hospital management teams receive voluminous data from a wide variety of sources, but are unable to distill the essential data they require to make good decisions. We have used a methodology which helps teams define and use important management data coupled with an information system that makes this data accessible. Results of our evaluation indicate that the process of developing a balanced scorecard (BSC) indicator system helps management teams to define meaningful strategic objectives and measurable performance indicators. The framework combined with the information acts as an integrating force, providing a shared understanding of the units goals. We conclude that a customized decision support system which integrates multiple measures in a BSC framework is a powerful tool for enabling complex decision making by a management team.

A Model for Studying Velocity Variations in Unmyelinated Axons

A simple electrical model of the nerve axon is presented. The only non-linear element in the model is the sodium conductance, which is assumed to vary in a step-like way. This allows the propagation velocity for action potentials to be expressed analytically. The aftereffects from an action potential are generally slow. By considering them quasi-stationary, the velocity of a subsequent action potential can be calculated and compared with that of the first one. Considering the effects of afterpotential and afterconductance, it is shown that the theory adequately describes the variations in propagation velocity in the squid giant axon for action potentials separated by 3 ms to 14 ms.