Surgical masks and blood shields worn by anesthesiologists and surgeons in hospital operating rooms may negatively impact speech communication and put patients at needless risk. Young adult subjects listened to sentences from the Speech Perception in Noise Test (SPIN) recorded by a male and female talker. All eight SPIN lists were recorded under three different speaking conditions: (1) speaking normally without any obstruction, (2) wearing a typical surgical mask, and (3) wearing a surgical mask with an attached blood shield. Multi-talker babble was mixed with the SPIN sentences at several signal-to-noise ratios to simulate conversation in noisy environments. Speaker gender and recording conditions were counterbalanced across listeners to control for learning and fatigue effects. SPIN test scores for each of the three types of recordings and both talker genders were compared in order to determine the degradation that blood-shields and surgical masks may have speech communication in the operating room. [Research supported by research grants from the Division of Social and Behavioral Sciences and a scholarship from the College of Arts and Sciences at The Ohio State University.]
Sensory dissonance is known to be related to the critical band [Greenwood (1961); Plomp and Levelt (1965)]. The maximum dissonance between two pure tones has been estimated to arise when the tones are separated by roughly 40% of a critical band [Greenwood (1991)]. Sensory dissonance disappears when the tones are separated by more than a critical band. Experimental work by Kameoka and Kuriyagawa (1969) has further demonstrated that dissonance judgments are affected by intensity. Since the size of critical bands are known to increase with increasing intensity [Moore and Glasberg (1987)], it follows that listeners should locate maximum dissonance at larger-frequency separations for higher-intensity tones. Similarly, the point at which dissonance disappears should involve larger frequency separation for higher intensity. The results of two experiments are reported where dissonance judgments were explicitly examined in the context of intensity-induced changes in critical bandwidth. In the first experiment, listeners adjusted the frequency of one tone away from a fixed tone to the point of maximum dissonance. In the second experiment, listeners adjusted the tone to the point of just-not-noticeable dissonance. Results will be reported for 10 musician and 10 nonmusician listeners.
Many elderly persons with high-frequency hearing loss find telephone use frustrating due to lower intensity levels and reductions in acoustical information that can be useful in deciphering speech. The purpose of this project is to pre-process the speech signal before it is sent over the phone line and provide speech enhancement without the use of amplifying handsets or hearing aids at the receiving end. The enhancement technique takes into account the limited bandwidth of the phone line as well as the hearing characteristics of the user. Two pre-processing schemes, a single channel and a double channel approach, used to increase the intelligibility of speech in these situations are discussed. The single channel method performs amplitude compression of the entire signal. The two-channel method filters the incoming signal into high-frequency and low-frequency channels and performs independent compression on each before recombination. Results comparing the two speech enhancement schemes against no processing for a group of elderly hearing-impaired subjects are presented. [Work supported by a grant from the Franklin County Office on Aging.]
In psychoacoustics, a multi-channel model has traditionally been used to describe detection improvement for multicomponent signals. This model commonly postulates that energy or information within either the frequency or time domain is transformed into a probabilistic decision variable across the auditory channels, and that their weighted linear summation determines optimum detection performance when compared to a critical value such as a decision criterion. In this study, representative integration-based channel models, specifically focused on signal-processing properties of the auditory periphery are reviewed (e.g., Durlach's channel model). In addition, major limitations of the previous channel models are described when applied to spectral, temporal, and spectrotemporal integration performance by human listeners. Here, integration refers to detection threshold improvements as the number of brief tone bursts in a signal is increased. Previous versions of the multi-channel model underestimate listener performance in these experiments. Further, they are unable to apply a single processing unit to signals which vary simultaneously in time and frequency. Improvements to the previous channel models are proposed by considering more realistic conditions such as correlated signal responses in the auditory channels, nonlinear properties in system performance, and a peripheral processing unit operating in both time and frequency domains.
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