These experiments were carried out to assess how accurately the gains and compression ratios in a two-channel compression system needed to be set. We used as a research tool a laboratory version of a two-channel full-dynamic-range compression system. The system was initially adjusted to suit each hearing-impaired subject according to the manufacturer's recommendations. Then, further adjustments were made to ensure that speech stimuli were both audible and comfortable over a wide range of sound levels. Finally, the settings of the gains and compression ratios were systematically varied from the adjusted values and the effects of this on the intelligibility of speech in quiet and in noise (12-talker babble, levels of 65 and 75 dB SPL) were measured. The results indicated that speech reception thresholds (SRTs) in quiet were significantly adversely affected by decreases in low-level gain. However, SRTs in noise were relatively unaffected by changes in low-level gain. An exception occurred at the higher noise level used, where increases in the low-level gains (with corresponding increases in compression ratios) had a significant adverse effect on the SRTs. It is concluded that, provided excessive low-level gains (associated with high compression ratios) are avoided, the main criteria for fitting such a system should be listening comfort (i.e. achieving an acceptable tonal balance, and avoiding uncomfortably loud sounds) and an appropriate value of the threshold for detecting speech in quiet (which should be a little below 50 dB SPL).
. Involving patients and parents in the choice of their cochlear implant encourages an active role in the process and facilitates 'bonding' and 'ownership' of the device. . The most frequent reasons given by patients for selecting a device included cochlear implant comfort and appearance. . We describe the Implant Programme based at the Royal National Throat, Nose and Ear Hospital, London, and also examine patient satisfaction with the scheme.
An unusual case of a patient with bilateral Meniere's disease is described whose disease presented in the second ear as a sensorineural hearing loss which fluctuated with the patient's level of blood glucose. The literature concerning the role of abnormal glucose metabolism in Meniere's disease is reviewed and the investigation and management of this patient's condition is discussed.
Modern cochlear implants (CIs) convey fundamental frequency (F0) information using a purely temporal code. However, temporal pitch processing - as measured by the discrimination of the changes in the rate of a pulse train applied to a single electrode - is often worse than in normal hearing (NH) at low pulse rates, and usually deteriorates dramatically at rates above about 300 pps. We will describe evidence that at low pulse rates, the value of the pitch perceived can be affected by refractory effects at the level of the auditory nerve (AN), and can also be influenced by small (< 0.5 dB) changes in stimulus level. In contrast, the deterioration in rate discrimination at high rates appears to be impervious to a wide range of manipulations that would be expected to strongly affect the representation of the stimulus at the level of the AN. One example of this is the finding that the variation in rate discrimination performance with baseline rate for single-pulse-per-period pulse trains correlates, across listeners, with discrimination of different rates of sinusoidal amplitude modulation imposed on a 5000-pps carrier. The implications of these findings for attempts to improve pitch coding in CIs will be discussed.
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