The many faces of neurofibromatosis.
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Adolescent↗
Biomedical subjects
B C Moore
Publications and source records attributed to B C Moore.
Fragile X-linked mental retardation of macro-orchidism.
A fragile site near the end of the long arm (q) of the X chromosome appears to be directly related to the gene responsible for the mental retardation found among males and some females who possess this variant X chromosome. Macro-orchidism is present in most males studied. Other mild phenotypic similarities may exist. The expression of the fragile X (fra[X]) chromosome is dependent on the concentration of folic acid and thymidine in the culture medium, which partly explains why fra(X) was not noted earlier and connected promptly with X-linked mental retardation. Whereas prenatal diagnosis is now possible, genetic counseling is complicated by recent reports of "intellectually normal" fra(X) males. Further studies are needed to form solid conclusions about intellectual deficits, learning behavior or personality characteristics of fra(X) persons.
Female↗
Voice pitch as an aid to lipreading.
The totally deafened adult, unable to make use of a hearing aid, has no alternative to lipreading for everyday communication. Lipreading, however, is no substitute for hearing speech. Many lipreaders have great difficulty in ideal conditions and even the best lipreaders find the task demanding and tiring. Prosthetic attempts to substitute for lost hearing have centred on three distinct types of intervention, visual, tactile, and electrocochlear. As none of these is likely to yield a good understanding of a speech independent of lipreading in the near future, we have attempted to isolate relatively simple patterns of stimulation that, although not intelligible in themselves, well aid lipreading. From this point of view, the fundamental frequency or 'pitch' of the voice is the most important pattern element because if provides both segmental and suprasegmental information and is practically invisible. It thus complements the visual information already available on the face. As we show here, with the voice pitch presented acoustically, normal listeners can lipread a speaker reading continuous text at up to two and a half times the rate possible on the basis of lipreading alone. The pitch signal by itself, of course, is completely unintelligible. Although our work is primarily concerned with methods of electrical stimulation of the cochlea, it has implications for other sensory substitution techniques, the design of special purpose hearing aids and current theories of speech perception.
Female↗
Improving psychoacoustical tuning curves.
The probe signal in psychoacoustical tuning curves stimulates more than one neuron, even when presented at low levels. The subject can "listen" to neurons with characteristic frequencies away from the nominal probe frequency and optimize performance. This "off-frequency listening" can account for much of the discrepancy in the sharpness of tuning between psychoacoustical tuning curves obtained in forward masking and neurophysiological tuning curves. By adding a band-reject noise, centred on the probe frequency, to limit off-frequency listening, results in close agreement with the neurophysiological data can be produced.
Acoustic Stimulation↗
Relation between pitch shifts and MMF shifts in forward masking.
Thresholds for brief sinusoidal signals were determined as a function of signal frequency for fixed sinusoidal maskers in a forward masking task. In some cases the frequency at which maximum masking occurred (MMF) was slightly above or below the masker frequency. In a second experiment subjects were required to adjust the frequency of the signals that its pitch matched that of the "masker." It was found that the frequency required for equal pitch correspond closely to the MMF. A possible explanation is that differences in quality between signal and masker (such as pitch differences) provide a cue for detection in forward masking which is not available when the signal and masker are very similar in quality. Thus maximum masking occurs when the signal and masker are most similar in quality.
Acoustics↗
Off-frequency listening: effects on psychoacoustical tuning curves obtained in simultaneous and forward masking.
Off-frequency listening--the use of information in different frequency regions to improve performance in masking tasks--has been reported to influence psychoacoustical tuning curves measured in simultaneous masking. The present experiment was designed to establish whether suppression has an effect on off-frequency listening. Psychoacoustical tuning curves were obtained from three observers in both simultaneous and forward masking. A probe level of 10 dB SL and narrowband noise maskers were used. After obtaining the conventional tuning curves, a fixed masker, at either 1.8 or 2.2 kHz and 10 dB below the corresponding tuning-curve threshold, was added to limit off-frequency listening. In both simultaneous and forward masking, the branch of the tuning curve opposite the fixed masker was shifted downwards, but to a greater extent in forward masking. The suppression of the probe in tuning curves measured in simultaneous masking appears to constrain off-frequency listening. In forward-masking tuning curves, off-frequency listening has a greater effect, and may explain to a large extent the very sharp tuning which has been found in some studies.
Auditory Threshold↗
Forward masking by sinusoidal and noise maskers.
A 2-kHz sinusoid and a narrow-band noise centered at 2 kHz, with the same total power, served as maskers for a 2-kHz sinusoidal signal. We compare the forward masking produced by these two maskers (1) as a function of offset--offset time for 5- and 35-ms signals, (2) as a function of signal duration for a fixed offset--onset time, and (3) as a function of signal duration for a fixed offset--offset time. In all these comparisons, we find that the noise and sinusoid not only produce different amounts of masking for the same experimental condition, but they also show different trends for the same manipulation. The important relations in these results are demonstrated in an additional set of conditions with a 1-kHz signal. In order to account for the differences observed in both experiments, we argue that forward masking is determined by at least two factors. We suggest signal energy as one factor and the presence or absence of differences in quality between masker and signal as another.
Audiometry↗
Interactions of masker bandwidth with signal duration and delay in forward masking.
Forward-masked thresholds for 1-kHz sinusoidal signals were measured as a function of the bandwidth of a noise masker centered at 1 kHz, using a two-interval forced-choice technique. The noise spectrum level was 40 dB SPL/Hz, and noise bandwidth was varied from 50 to 1600 Hz. In experiment I signal duration was varied, with a fixed offset-onset time of 5 ms between masker and signal. For the shortest signal (5 ms) threshold at first increased with increasing bandwidth and then decreased. As signal duration increased, the bandwidth at which maximum masking occurred (the rollover bandwidth) decreased, and for the longest signal (45 ms) maximum masking occurred for the narrowest bandwith tested. In experiment II the silent interval between masker and signal was varied, for a signal of 5-ms duration. Again threshold at first increased with noise bandwidth, and then decreased. However, the rollover bandwidth decreased with increasing silent interval, and threshold varied less with bandwidth. In experiment III signal duration was varied for a fixed offset-offset time of 50 ms between masker and signal. Changes in threshold with noise bandwidth were small, except for the longest signal (45 ms) for which threshold increased markedly at the narrowest bandwidth used. For the wider nose bandwidths, threshold decreased gradually with increasing signal duration, whereas for the narrowest noise bandwidth, threshold increased with increasing duration. It is argued that interactions of excitation and suppression within the internal representation of the masker influence the results, but at least two other factors, detection of energy splatter in the spectrum of the signal and the presence or absence of quality differences between masker and signal, have a powerful influence.
Acoustics↗
Effect of probe duration on psychoacoustical tuning curves obtained in forward masking.
The duration of the probe affects the sharpness of tuning of psychoacoustical tuning curves obtained in forward masking. With probes of less than 30 ms, a major factor appears to be the increase in the frequency spread of spectral energy with decreasing duration. Even with low-level probes, the redistribution of energy within the mainlobe of the spectrum is considerable and increases off-frequency listening.
Acoustic Stimulation↗
Auditory filter shapes derived in simultaneous and forward masking.
In this paper we describe a method for comparing frequency selectivity in simultaneous and forward masking. The method is designed to eliminate off-frequency listening, which may have had a confounding influence in earlier studies. Thresholds for 1-kHz sinusoidal signals were measured as a function of the width of a spectral notch, centered at 1 kHz, a noise masker. In experiment I thresholds were measured in forward masking for signal durations of 5, 15, and 45 ms, with a noise spectrum level of 40 dB SPL/Hz. Thresholds decreased with increasing notch width for all signal durations. However, the change was more gradual at longer signal durations. This is consistent with a model in which the process of decay of masking follows the auditory filter. For each signal duration, threshold was also measured as a function of the level of a noise without a spectral notch. Each signal threshold for the notch-noise condition was then expressed as the level of a flat-spectrum noise which would give the same masking. When transformed in this way, the data for the three signal durations coincide, and can be interpreted in terms of the same auditory filter. In experiment II the 5-ms signals, whose level was fixed, followed the masker with delays of 5, 15, or 25 ms. The noise spectrum level was varied to find threshold. The change in threshold with notch width was independent of signal delay, confirming that the process of decay of masking follows the auditory filter. Experiment III showed that short-term spectral changes produced by differences in the shapes of the envelopes of signal and masker did not influence the results. In experiment IV thresholds for a 5-ms signal were measured in simultaneous and forward masking, both for a fixed noise level and for a fixed signal level. The derived auditory filters are similar for the two types of measure for each type of masking. However, the auditory filters derived in forward masking have bandwidths 17% smaller and slopes 48% greater than those in simultaneous masking. The differences between simultaneous and forward masking are interpreted in terms of suppression.
Acoustic Stimulation↗
Fragile X-linked mental retardation.
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Ethnicity↗
Mechanism and frequency distribution of two-tone suppression in forward masking.
These experiments are concerned with the frequency distribution of two-tone suppression in forward masking. In each experiment the threshold of a 20-msec probe tone following a 300-msec masker was determined as a function of probe frequency. In experiments I and II this was done for two maskers (a single tone with frequency fm, and that tone with a suppressive tone added) which had previously been equated for their masking effectiveness at fm by adjusting the levels of the components at fm. The maskers were equally effective only in a restricted frequency region around fm, a result which is not consistent with the idea that suppression is equivalent to a simple reduction in level of the suppressed tone. In experiment III probe thresholds were measured for a fixed tone at 2 kHz with and without a suppressing tone whose frequency was systematically varied. The suppression, measured as the reduction in probe threshold produced by adding the suppressing tone, was found to have two components. One of these was limited to a narrow range of probe frequencies around 2 kHz and is attributed to a qualitative change in the cues available to the observer when a suppressing tone is added to the masker. The other component shifted in frequency as the suppressor frequency was altered and is explained as a reduction in level of only part of the excitation pattern of the suppressed tone.
Adolescent↗
Neural interspike intervals and pitch.
In a recent paper, Whitfield [1979] reported that time intervals between successive nerve impulses were not necessarily a correlate of pitch. This conclusion was reached by considering harmonics outside the dominant region for pitch perception [Ritsma, 1967]. The pitches perceived by Whitfield's subjects can be predicted from the harmonics present in the dominant region, and time intervals corresponding to those pitches would have been present in nerve fibers with characteristic frequencies close to that region.
Humans↗
The fragile X chromosome mental retardation and large testes.
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Female↗
Tune recognition with reduced pitch and interval information.
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Acoustic Stimulation↗
External electrical stimulation of the cochlea: clinical, psychophysical, speech-perceptual and histological findings.
Our progress towards the development of a particular form of cochlear implant for the totally deaf is described. A single channel stimulation at the round window or promontory is used. This involves a minimum of surgical intervention and infective risk, preserves the possibility of remission and allows the application of later developments. The signal used for stimulation is designed to be matched both to the deaf lip-reader's needs and to his new, restricted, auditory ability. This is done by concentrating on the acoustic pattern components of speech which carry intonation and voiced-voiceless information. Surgical electrophysical, psychoacoustic and speech perceptual aspects of our work with twelve patients are described. The tests involve responses, for example, relating to: threshold for sinusoids; frequency difference limens; periodic -aperiodic discrimination; stress placement; and consonant labelling using combined visual and electrical inputs. Relatively extensive measurements were made with six patients. Significant individual differences were found and the sets of responses provide an essential basis for an appraisal of the potential usefulness of our work to the individual patient. Possible reasons for the individual differences are discussed. A brief indication is given of the techniques which we have developed for the future speech training and speech production evaluation of patients with electro-cochlear voice monitoring. The final section of our paper mentions our histological investigation of the effects of this type of stimulation in the guinea pig.
Acoustic Impedance Tests↗
'Electrical auditory stimulation in the management of profound hearing loss'.
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Cochlea↗