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Biomedical subjects

C Formby

Publications and source records attributed to C Formby.

At least 37 records · Page 2Linked to original sources
PubMed1989

Regional cerebral blood flow for singers and nonsingers while speaking, singing, and humming a rote passage.

Two groups of singers (n = 12,13) and a group of nonsingers (n = 12) each produced the national anthem by (1) speaking and (2) singing the words and by (3) humming the melody. Regional cerebral blood flow (rCBF) was measured at rest and during each phonation task from seven areas in each hemisphere by the 133Xe-inhalation method. Intrahemisphere, interhemisphere, and global rCBF were generally similar across phonation tasks and did not yield appreciable differences among the nonsingers and the singers.

Adult↗
PubMed1989

Preliminary evaluation of a Weibull function for fitting slow-component eye velocity over the time course of caloric-induced nystagmus.

We describe preliminary attempts to fit a mathematical function to the slow-component eye velocity (SCV) over the time course of caloric-induced nystagmus. Initially, we consider a Weibull equation with three parameters. These parameters are estimated by a least-squares procedure to fit digitized SCV data. We present examples of SCV data and fitted curves to show how adjustments in the parameters of the model affect the fitted curve. The best fitting parameters are presented for curves fit to 120 warm caloric responses. The fitting parameters and the efficacy of the fitted curves are compared before and after the SCV data were smoothed to reduce response variability. We also consider a more flexible four-parameter Weibull equation that, for 98% of the smoothed caloric responses, yields fits that describe the data more precisely than a line through the mean. Finally, we consider advantages and problems in fitting the Weibull function to caloric data.

Adult↗
PubMed1989

Effects of randomizing signal level and duration on temporal gap detection.

Although discriminable changes in stimulus energy or overall duration may accompany the silent temporal gap, there is little evidence that these extraneous cues confound the measurement of temporal gap detection threshold. In this report we show that (1) under conditions where gap detection thresholds are large in relation to the duration of the standard, extraneous cues may confound gap detection leading to underestimates of the true threshold, and (2) randomization of overall stimulus level and duration can successfully remove confounding energy and duration cues without distracting the listener's attention from the temporal-gap cue.

Adult↗
PubMed1988

Correlations between hearing thresholds and caloric responses among a heterogeneous sample of dizzy patients.

Auditory and vestibular function were compared in a heterogeneous sample of dizzy patients (N = 52). Hearing thresholds for the conventional audiometric frequencies were measured for each patient and parceled into two frequency ranges, 0.25-1 kHz and 2-8 kHz. Hearing thresholds also were measured for each patient over an extended high-frequency range that included the frequencies 10, 12, and 14 kHz. Bithermal caloric responses for these patients were available and were grouped for unilateral weakness (UW) or no unilateral weakness (NOUW). Hearing thresholds ipsilateral to the side of unilateral weakness (UW) yielded significant (p less than .05) modest correlations (r = .39-.52) with UW for all three audiometric frequency ranges (N = 35). These findings do not suggest a strong tonotopic relation between the audiometric and UW data. Hearing thresholds for the frequency range 10-14 kHz, but not for the conventional audiometric frequencies, correlated with slow-phase eye velocity (SPV) when SPV was averaged across the four caloric conditions for each of 17 NOUW patients. The latter finding indicates a subtle trend for eye velocity to increase as a function of increasing hearing threshold.

Adolescent↗
PubMed1988

Modulation and gap detection for broadband and filtered noise signals.

Modulation detection thresholds (as a function of sinusoidal amplitude modulation frequency) and temporal gap detection thresholds were measured for three low-pass-filtered noise signals (fc = 1000, 2000, and 4000 Hz), a high-pass-filtered noise signal (fc = 4000 Hz), and a broadband signal. The two latter noise signals were effectively low-pass filtered (fc = 6500 Hz) by the earphone. Each of the filtered signals was presented with a complementary filtered noise masker. Modulation and gap detection thresholds were lowest for the broadband and high-pass signals. Thresholds were significantly higher for the low-pass signals than for the broadband and high-pass signals. For these tasks and conditions, the high-frequency content of the noise signal was more important than was the signal bandwidth. Sensitivity (s) and time constant (tau) indices were derived from functions fitted to the modulation detection data. These indices were compared with gap detection thresholds for corresponding signals. The gap detection thresholds were correlated inversely (rho = -1.0, p less than 0.05) with s (i.e., smaller gap detection thresholds were correlated with greater sensitivity to modulation), but were not correlated significantly with tau, which was relatively invariant across signal conditions.

Adult↗
PubMed1987

The effects of continuous phonation on 133xenon-inhalation air curves (of the kind used in deriving regional cerebral blood flow).

Regional cerebral blood flow (rCBF) may be measured with inhalation techniques that use end-expired values of radioactivity to estimate the isotope concentration in arterial blood. These end-expired data are used as an input function in a mathematical equation to derive rCBF. End-expired air is assumed normally to be in equilibrium with the arterial blood at the alveolar surface of the lung during regular (passive) breathing; this assumption may not be valid during continuous phonation. We therefore have analyzed breathing (inhalation/exhalation) patterns and end-expired radioactivity (133Xe) during (1) speaking, (2) singing, and (3) humming of the national anthem, and also during (4) passive breathing. Statistically significant differences in breathing patterns were measured between a group of nonmusicians and two groups of musicians (singers) during the phonation tasks: The nonmusicians breathed more often (and more rapidly) and exhibited less variability in their breathing patterns than did the musicians. Notwithstanding these differences, the shapes of smoothed functions derived from the end-expired values were not influenced appreciably during phonation (except possibly during talking). The latter finding suggests that estimates of rCBF derived with these data should not be confounded seriously because of the continuous phonation.

Adolescent↗
PubMed1987

Hearing loss among stroke patients.

Pure-tone hearing thresholds were measured by air conduction for 140 right hemiplegic and 103 left hemiplegic patients who had suffered a single stroke. Statistical and informal testing of the mean audiometric thresholds revealed that: (1) the ability of the aphasic patient to attend to and to perform the audiometric test was independent of the severity of the aphasic impairment; (2) aphasic patients did not suffer disproportionately greater hearing losses than did other right hemiplegic stroke patients; (3) no relation was apparent between the severity of the hearing loss and the test ear or side of hemiplegia after stroke; (4) the severity of high-frequency hearing loss among stroke patients was consistent with that found in the elderly male population at Framingham, MA (Moscicki, Elkins, Baum, and McNamara, Ear Hear 1985;6:184-90); and (5) the prevalence of hearing loss among the stroke patients was greater than that reported at Framingham, but was consistent with rates found among elderly nursing home residents.

Adult↗
PubMed1987

Modulation threshold functions for chronically impaired Menière patients.

Detection thresholds for sinusoidally amplitude-modulated broad-band noise were measured as a function of modulation frequency for both ears of 6 chronic Menière patients who suffered unilateral hearing impairments. Modulation thresholds were measured with an adaptive cued-standard forced-choice psychophysical method. Better-ear modulation thresholds were similar to normative data previously reported [Formby, C.: J. acoust. Soc.Am. 78:70-77, 1985], whereas 5 of the 6 patients exhibited deficits in modulation detection with their poorer ears. Modulation thresholds averaged across the patients' poorer ears were similar to the normative thresholds through 60-100 Hz; at higher modulation frequencies, sensitivity declined at approximately twice the normal attenuation rate (i.e., 6 vs. 3 dB per octave). The poorer-ear data can be described by the mathematical representation for a simple low-pass filter with a cutoff frequency of 60 Hz. This pattern of the Menière modulation thresholds is consistent with broadened peripheral tuning due to hydrops.

Adult↗
PubMed1986

Modulation detection by patients with eighth-nerve tumors.

Detection thresholds for sinusoidally amplitude-modulated broad-band noise were measured as a function of modulation frequency for 4 normally hearing listeners and for 6 patients suffering eighth-nerve tumors. Measurements were obtained using a method-of-adjustment (MOA) procedure. On average, the threshold values revealed that more modulation was needed across all modulation frequencies for the patients' affected ears relative to either the normally hearing listeners or the patients' better ears. The cutoff frequency derived from the average modulation-threshhold function (MTF) for the affected ears was about half the normal value. For a simple lowpass-filter model of the process, the latter result suggested a doubling of the auditory time constant in the affected ears. These patients, on average, exhibited the characteristic high-frequency audiometric hearing loss most often associated with eighth-nerve tumors. Their MTFs closely resembled MTFs described previously for high-frequency audiometric hearing loss. The results of statistical analyses suggested that high frequency audiometric hearing loss, irrespective of other influences, is the most parsimonious explanation for the increased modulation thresholds measured for the eighth-nerve tumor patients.

Adult↗
PubMed1986

Changes in caloric nystagmus induced by vasodilating drugs.

Systemic blood flow, blood flow to the peripheral skin, middle ear, and temporal bone, and that to the inner ear of normal volunteers was manipulated selectively through the use of vasodilator drugs. The effect of selective vasodilation was monitored via changes in the temporal course of the slow-phase velocity of nystagmus evoked by bithermal caloric irrigation. Drug influenced eye velocities were compared with control values measured before drug administration. Eye velocities measured after niacin (a peripheral vasodilator) administration generally were greater than control values, whereas eye velocities measured after papaverine (a central vasodilator) and histamine (a systemic vasodilator) administration typically were less than control values. These findings, with the exception of the cool caloric/niacin condition, are consistent with a model of vestibular dynamics and measurements of cochlear blood flow in animal models.

Adult↗
PubMed1986

Frequency and rate discrimination by Menière patients.

Discrimination tests were conducted for each ear of 6 patients with unilateral Menière's disease. Differential sensitivity to changes in pure-tone frequency (presumably containing temporal and place cues) was compared to differential sensitivity to changes in rate of sinusoidally amplitude-modulated noise (presumably containing only a temporal cue) at common low frequencies and modulation rates (less than 400 Hz). An adaptive forced-choice psychophysical procedure was used. The better-ear results for the Menière patients generally were similar to findings for normally hearing listeners. For the impaired ears, pure-tone frequency discrimination typically was impaired relatively more than was the rate discrimination up to 200 Hz. However, rate discrimination was difficult or impossible above 250-300 Hz. Absolute frequency difference limens (DLs) were, on average, smaller than or at least equivalent to absolute rate DLs. Moreover, frequency discrimination always was possible for the Menière patients.

Adult↗
PubMed1985

Tonotopic organization in human auditory cortex revealed by positron emission tomography.

Positron emission tomography (PET) was used to map alterations in local neuronal activity induced in human primary auditory cortex by pure-tone stimulation. Patterns of blood flow were observed in specific regions on the superior temporal plane showing systematic changes in activity depending on the frequency of a stimulating pure tone. The orientation of these regions agrees well with data for non-human primates.

Acoustic Stimulation↗
PubMed1985

Differential sensitivity to tonal frequency and to the rate of amplitude modulation of broadband noise by normally hearing listeners.

Differential sensitivities for tones which varied in frequency (containing cues for place and periodicity) and for broadband noise which varied in the rate of sinusoidal amplitude modulation (presumably containing only a periodicity cue) were measured at common frequencies and modulation rates of the stimulus for four normally hearing listeners. A forced-choice adaptive psychophysical procedure was used in all measurements. Through 60 Hz, tonal-frequency and rate discrimination were similar (on average, 2.5-3.0 Hz) across listeners. From 80-400 Hz, differential sensitivity for tones was between 1.0 and 2.0 Hz, whereas values for rate discrimination increased almost linearly from about 3.6 to 122.0 Hz. Apparently, differential sensitivities for both tonal frequency and modulation rate are mediated similarly, presumably by the same (periodicity) mechanism, through 60 Hz. Above 60 Hz, the listener is more sensitive to differences in tonal frequency than modulation rate. Detection thresholds for sinusoidal amplitude modulation of noise also were measured for these listeners. An average modulation threshold function was obtained and a half-power frequency was estimated for the function at 60 Hz; from this value a time constant of 2.65 ms may be derived, which is consistent with time constants measured by other psychophysical methods. These data further point to some change in perceptual quality above about 60 Hz, that frequency above which we found tonal-frequency and rate discrimination functions to separate.

Adult↗
PubMed1984

Frequency selectivity and thresholds of brief stimuli suitable for electric response audiometry.

Auditory evoked potentials are nearly all on-effects and the 'effective stimuli' for them are necessarily brief. Their frequency specificity is therefore limited, especially for the brainstem responses, because of the well-known trade-off between duration and frequency specificity. Brainstem responses are of special interest because they are unchanged in the sleep-like sedation that is required for difficult-to-test children. The middle-latency responses do not meet this requirement. Two patterns of tone burst that are appropriate and promising for the slow cortical potentials and for brainstem potentials, respectively, have rise and fall times of 2 periods of the modulated tone and plateaus of 10 (or 7) periods and 1 period, respectively. Their behavioral thresholds are nearly insensitive to difference in repetition rate between 4 and 40 stimuli/s. Their peak equivalent SPL threshold values at 500, 1 000, 2 000 and 4 000 Hz have been determined for 16 otologically normal ears. Using these reference levels, audiograms have been obtained for subjects with impaired hearing. The audiograms for 'flat' hearing losses do not differ significantly from the corresponding conventional pure-tone audiograms. The slopes for steep high-frequency hearing losses are underestimated, however, particularly with the brief (2-1-2) pattern. Nevertheless, the 2-1-2 pattern appears to be close to the best possible compromise.

Acoustic Stimulation↗
PubMed1982

Long-term average speech spectra for normal and hearing-imparied adolescents.

Acoustical aspects of the speech of hearing-imparied persons have usually been examined over brief periods of time for simple utterances. Of interest in this study was whether abnormal acoustical patterns would be observed when speech was examined over longer periods of time. Spectra were averaged for 20 hearing-impaired adolescents, for whom we had audiometric profiles and an assessment of speaker intelligibility, and also for ten normal-hearing adolescents. An analyzer having constant-frequency bandwidths of 60 Hz, with the center frequencies of the filters spaced at 40-Hz intervals across a 10-kHz range, was used in the measurements (averaging time 27 s). The normal spectra are characterized by a regular pattern of peaks occurring at multiples of the talkers' fundamental frequencies and by slopes declining at rates of -5 to -6 dB/octave. After correction for lip-radiation impedance, these slopes are similar to that reported for the normal glottal source ( - 12 dB/octave). The hearing-impaired adolescents produced spectra for which the harmonic structure ranged from the very well defined to the irregular and poorly defined; spectral slopes declined at rates equal to or greater than the normal rate, in some cases declining at twice the normal rate.

Adolescent↗
PubMed1981

Some systematic observations on monaural diplacusis.

Anomalies of monaural pitch perception, including pitch changes with level, roughness and beats, were mapped in the intensity-frequency plane by a listener using continuous-tone stimulation between approximately 1 900 and 2 750 Hz. A narrow region characterized by rapid threshold adaptation was also mapped between approximately 2 590 and 2 690 Hz. In the procedure used to localize the internally generated tones, which were interacting with the externally presented single tones to produce beats, the listener adjusted the frequency of a signal presented to this right ear so that the beat rate heard there was the same as a criterion beat rate produced by two external tones in his left ear. A plot in the intensity-frequency plane of adjustments for a constant-beat rate revealed a remarkable correspondence to the region of adaptation (between 2 590 and 2 690 Hz) in that the former curve was simply shifted in frequency away from the latter by an amount equal to the two-tone interval producing the beat rate. Thus, the locations of 'internal tones' correspond predictably to both the lower and upper-frequency boundaries of the region of adaptation. Pitch changes, as a function of signal level, at frequencies below the region of adaptation were also investigated and appear to reflect a change from interaction to cessation of interaction between the signal and the region of adaptation. The locus of these pitch-related abnormalities, over a broad range of frequencies, points to interaction between that range and a smaller-frequency region where abrupt transitions in sensitivity occur.

Acoustic Stimulation↗
PubMed1980

Psychophysical tuning curves for combination tones 2f1-f2 and f2-f1.

A simultaneous masking paradigm was employed to demonstrate that combination tones are "stimulus-like" in nature. Three musically sophisticated listeners adjusted the level of pure tones at various frequencies to just mask a pulsing signal corresponding to a tone at 1200 Hz and 20 dB SPL. The signal was produced by four stimulus conditions: (1) a pulsing tone at 1200 Hz; (2) a combination tone at 2f1-f2 = 1200 Hz produced by a continuous f1 at 1650 Hz and a pulsing f2 at 2100 Hz; (3) a control for condition 2 with a pulsing tone at 1200 Hz and a continuous f1 at 1650 Hz; and (4) a combination tone at f2-f1 = 1200 Hz produced by a continuous f1 at 1900 Hz and a pulsing f2 at 3100 Hz. Across subjects and stimulus conditions the shapes of the tuning curves were similar; whether for an externally presented single tone or a combination tone, minimum masker level (which corresponds to the tuning-curve "tip," the frequency at which masking is most effective) was always at frequencies near 1200 Hz. These findings are consistent with previous psychophysical as well as recent physiological evidence which indicates that, regardless of how generated, each of the combination tones 2f1-f2 and f2-f1 is present in the motion of the basilar membrane in the cochlear region around the characteristic place of the combination-tone frequency.

Acoustic Stimulation↗