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Biomedical subjects

B Scharf

Publications and source records attributed to B Scharf.

At least 55 records · Page 3Linked to original sources
PubMed1984

Localized pontine lesion: nearly total absence of REM sleep.

Eight whole-night polysomnographic recordings were conducted in a 33-year-old man with a localized pontine lesion inflicted by a shrapnel fragment. Sleep recordings revealed no rapid eye movement (REM) sleep in 3 nights, and markedly reduced REM sleep in 5 nights; non-rapid eye movement (NREM) sleep was normal. In spite of marked reduction of REM sleep, the patient conducted a normal life and had none of the typical symptoms of REM-sleep deprivation.

Adult↗
PubMed1984

Auditory middle latency-evoked potentials during sleep apnea.

Auditory middle-latency evoked potentials (AMEP) were recorded in 10 subjects with predominantly central sleep apnea. AMEP were recorded during: waking; non-rapid eye movement (non-REM) sleep between apneic episodes; first half of apneas; and second half of apneas. Latencies of vertex positive peaks Po and Pa were determined, and the effect of the apnea phase on these latencies was evaluated. The latencies measured did not reveal chronic or acute functional abnormality of central auditory structures, which may result from or cause apneic episodes during non-REM sleep. The normalcy and stability of AMEP during apneic sleep may indicate effective compensatory mechanisms in central auditory structures. Alternatively, the lack of changes may result from the variability of AMEP, which may obscure small functional changes.

Adult↗
PubMed1983

Auditory brainstem evoked potentials during sleep apnea.

Auditory brainstem evoked potentials (ABEPs) were recorded from seven subjects with predominantly central sleep apnea. ABEPs were recorded during: (1) waking, (2) non-REM sleep between apneic episodes, (3) first half of apneas, and (4) second half of apneas. Latencies of vertex positive peaks III, V, and VI as well as the V-III interpeak latency difference were determined, and the effect of apnea phase on these measures were evaluated. The measures studied did not reveal chronic or acute functional abnormality of auditory brainstem, which may result from or cause apneic episodes during non-REM sleep. The normality and stability of ABEPs during apneic sleep indicate effective compensatory mechanisms in auditory brainstem. Brainstem functional changes associated with central apneas may not be reflected in the ABEP measures studied, unless they are part of a more extensive dysfunction.

Adult↗
PubMed1983

Loudness adaptation, when induced, is real.

In two recent articles, Hood and Wade (1982) and Weiler et al. (1981) have argued that the loudness of a steady tone does not appear to decline over time unless listeners are given a reference sound by which to judge loudness. The present experiments show, by the method of successive magnitude estimation, that listeners do not need a reference sound in order (1) to track accurately the decline in the loudness of a tone slowly decreasing from 60 to 40 dB SPL or (2) to track the loudness decline of a constant-intensity tone under special conditions that lead to adaptation. Since a reference sound is not needed by listeners to track a decline in loudness, and since Hood and Wade and Weiler et al. have found a decline with a reference but not without, it follows that adding a reference sound to a sustained sound must induce adaptation that otherwise does not occur. In support of that interpretation, the present measurements show that when subjects are told to ignore the same reference sound as used by Hood and Wade and by Weiler et al.--an increment every 30 s to a steady tone--loudness still declines. The bigger the increment (20 dB v. 5 dB) and the longer (5 s v. 1 s), the more loudness declines. Thus, loudness adaptation may be induced not only by a contralateral intermittent sound (Botte et al., 1982) but also by an ipsilateral intermittent sound. However, under normal listening conditions at levels above about 30 dB SL, loudness does not adapt.

Acoustic Stimulation↗
PubMed1982

Loudness adaptation induced by an intermittent tone.

The loudness of a continuous 1000-Hz tone at 60 dB SPL was measured in the presence of an intermittent tone in the contralateral ear. Over 70 observers participated in a series of eight experiments. The method of successive magnitude estimation showed that the intermittent tone causes the steady tone to diminish in loudness within 2 or 3 min by 40% to 60%. The amount of this induced loudness adaptation depends weakly upon the presentation rate, frequency, and level of the contralateral tone. Loudness reduction of the steady tone is coupled with loudness enhancement of the intermittent tone in the opposite ear. Induced loudness adaptation was also revealed by interaural and cross-modality matching. Induced loudness adaptation depends strongly on interaural interaction and is probably related to lateralization and interaural funneling of loudness. Adaptation induced by an intermittent tone stands in marked contrast to the near absence of loudness adaptation, except near threshold, when a continuous sound is presented alone.

Acoustic Stimulation↗
PubMed1981

Auditory brain stem evoked potentials: clinical promise of increasing stimulus rate.

Auditory brain stem evoked potentials (ABEPs) were recorded from 10 adults and 10 children who where neurologically and audiometrically normal. ABEPs were recorded in response to 75 dB HL clicks presented at rates of 10/sec and 50/sec. Normative values were calculated for amplitude and latency, as well as for inter-peak amplitude ratio and a variety of inter-peak latency differences and interaural differences at the two stimulus presentation rates. Normative values of the effect of increasing stimulus rate were calculated as well. Measures of changes in ABEPs between stimulus rates of 50/sec and 10/sec were the only derived measures that were significantly different between our adult and child normal populations. In addition, 50 patients with various conditions affecting the brain stem were examined. Increasing stimulus presentation rate had a significant effect on detection of abnormality in ABEPs from the patients examined. Measures of changes in ABEPs between stimulus rates of 50/sec and 10/sec seemed to be sensitive to a subset of abnormalities in our patient population. The case histories of the patients indicate that the subset may be impaired synaptic function. Measures of the effect of rate on ABEPs may complement the traditional measures that are primarily sensitive to white matter lesions.

Acoustic Stimulation↗
PubMed1980

Frequency selectivity in normally-hearing and hearing-impaired observers.

This study compares frequency selectivity--as measured by four different methods--in observers with normal hearing and in observers with conductive (nonotosclerotic), otosclerotic, noise-induced, or degenerative hearing losses. Each category of loss was represented by a group of 7 to 10 observers, who were tested at center frequencies of 500 Hz and 4000 Hz. For each group, the following four measurements were made: psychoacoustical tuning curves, narrow-band masking, two-tone masking, and loudness summation. Results showed that (a) frequency selectivity was reduced at frequencies where a cochlear hearing loss was present, (b) frequency selectivity was reduced regardless of the test level at which normally-hearing observers and observers with cochlear impairment were compared, (c) all four measures of frequency selectivity were significantly correlated and (d) reduced frequency selectivity was positively correlated with the amount of cochlear hearing loss.

Hearing Loss↗
PubMed1978

Comparison of normal and impaired hearing. I. Loudness, localization.

Impaired hearing is characterized by high thresholds and reduced loudness. Loudness, however, may quickly recover as it increases rapidly from an elevated threshold. This rapid growth, known as loudness recruitment, is a sign of cochlear impairment and is generally not seen in conductive or retrocochlear impairment. Loudness recruitment means that the hard-of-hearing person detects small changes in intensity near his elevated threshold but he probably does no better than a normal listener at the same SPLs. Recruitment is often accompanied by reduced loudness summation, which means that the loudness of a band of noise does not increase as much with increasing bandwidth as in normal hearing. This reduced summation of loudness is probably why the cochlearly impaired ear has nearly the same threshold for the acoustic reflex to pure tones as to wide-band noise, whereas the normal ear has a much lower threshold to wide-band noise. Corresponding differences between normal and impaired hearing are not found in auditory localization. Rather, the evidence suggests that persons with residual hearing learn to localize sounds reasonably well. Even the inability of many hearing impaired persons to understand a speaker in a noisy environment may result more from a failure of frequency analysis rather than of localization.

Auditory Threshold↗
PubMed1978

Comparison of normal and impaired hearing. II. Frequency analysis, speech perception.

Frequency analysis covers two separate listening tasks, one involving frequency discrimination, the other frequency selectivity. Discrimination refers to the ability to distinguish one frequency from another. Selectivity refers to the ability to hear one frequency in the presence of other frequencies. Selectivity is critical to the understanding of speech which comprises sounds containing many different frequencies. To understand speech easily, the listener must be able to analyze speech sounds into their component frequencies, especially formants. The hard-of-hearing person is probably less able to make that analysis, but we know surprisingly little about either discrimination or selectivity in hearing impairment. Existing evidence does suggest that both discrimination and selectivity are reduced in cochlear impairment so that such patients need a bigger frequency difference to discriminate between two tones and they have a wider critical band. A widened critical band would be expected to make it very difficult for the severely impaired person to understand speech under all listening conditions; it would make it difficult for the moderately impaired person to understand speech in a noisy background, unless the signal-to-noise ratio is improved as is possible by appropriate amplitude compression in hearing aids.

Audiometry, Pure-Tone↗
PubMed1976

Critical band in auditory lateralization.

A new and powerful procedure for determining frequency analysis in the auditory system, as evidence by the critical band, is described. The onset time difference, delta T, needed to lateralize 30-msec tone bursts toward the leading ear was measured as a function of the frequency difference, delta F, between the brust in one ear and the burst in the other ear. When delta F was less than the critical band, threshold delta T was constant at 100 mu sec or less, depending on center frequency; beyond the critical band, delta T increased with delta F. These dichotically measured critical bandwidths increased from 110 Hz at a center frequency of 500 Hz to 1100 Hz at a center frequency of 6000 Hz. They were unaffected by varying signal level from 25 to 80 dB or signal duration from 10 to 300 msec. The sam e critical-band values have been measured with monaural stimuli in loudness summation, maskin, detection, phase perception, consonance, and so forth.

Acoustic Stimulation↗