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Biomedical subjects

R H Margolis

Publications and source records attributed to R H Margolis.

At least 73 records · Page 4Linked to original sources
PubMed1981

Detection of tones in band-reject noise.

Three experiments were conducted to investigate the detectability of tonal signals simultaneously presented with computer-generated, long duration (.5 sec), band-reject maskers. In Experiment 1, detectability of a tone of 500, 1000, or 2000 Hz presented at 50 dB SPL was measured as a function of the width of a spectral "notch" symmetrically placed around the tone. A narrow notch resulted in decreased detectability relative to the wide band (zero-notch width) control condition. Further increases in notch width resulted in increased detectability until subjects approached errorless performance. In Experiment 2, psychometric functions were obtained for a 1000-Hz tone presented in four notch-noise conditions. The slopes of the psychometric functions were consistently steeper in the band-reject conditions relative to the zero notch-width condition. These slope differences result in relationships between threshold and notch width that depend upon the region of the psychometric function from which the threshold estimates are obtained. In Experiment 3, the decrease in performance associated with the notch was found to increase in proportion to notch depth. The data suggest that spectral edges placed in the immediate vicinity of a tone reduce the detectability of the tonal signal. This "edge effect" is discussed in relation to two-tone inhibition that has been observed in the auditory nerve.

Acoustic Stimulation↗
PubMed1980

Acoustic-reflex thresholds for noise stimuli.

The effect of noise bandwidth on the acoustic-reflex threshold was studied in 12 normal-hearing adult subjects by independently varying the cutoff frequencies of low-pass (fL = 100 Hz) and high-pass (fH = 6000 Hz) computer-generated noises. Adjusting the cutoff frequency of the low-pass or high-pass activating stimuli over the 700-6000 Hz range resulted in a change in the reflex threshold of 4 dB/octave. As the cutoff frequency of the low-pass noise was reduced below 700 Hz, more rapid increases in reflex thresholds occurred. For high-pass stimuli, very small changes in reflex thresholds were noted as the lower cutoff frequency was increased from 100 to 700 Hz. The data suggest that between 700 and 6000 Hz equal spectral regions of a noise stimulus contribute equally to the reflex threshold, and that energy below 700 Hz contributes little to the sensitivity of the reflex.

Acoustic Stimulation↗
PubMed1978

Adaptation of the acoustic reflex.

The characteristics of acoustic reflex adaptation were studied in human subjects. Contralateral stapedial reflex measurements were made by monitoring changes in acoustic conductance and susceptance with a 220-Hz probe. The reflex activators included four tonal stimuli (500, 1000, 2000, and 4000 Hz) and broadband noise presented for 180 s at 96, 104, and 112 dB SPL. The data are presented as change in acoustic admittance and in percent of maximum admittance change. The static admittance of the ear was found to drift systematically toward lower admittance values in the absence of contralateral stimulation. All stimulus conditions demonstrated some reflex adaptation. The half-life and time of onset of adaptation were found to vary directly with intensity and inversely with frequency. The effects of stimulus parameters on the rates of reflex adaptation are discussed. A previously described exponential model of reflex adaptation provided a reasonable first approximation to the data.

Acoustic Stimulation↗
PubMed1977

A comparison of three methods for predicting hearing loss from acoustic reflex thresholds.

Previously reported acoustic reflex threshold data from normal and hearing-impaired subjects indicate that the effect of stimulus bandwidth on reflex thresholds is altered by sensorineural hearing loss. It is this change in the "bandwidth effect" that forms the basis for predicting hearing loss from reflex threshold data. Three predictive procedures were compared for 17 normal and 60 hearing-impaired ears. All methods correctly identified most hearing losses but none of the methods accurately estimated magnitude of hearing loss. Two methods were characterized by a high rate of false positives. The third was tailored to minimize false positives (6%) and maintain a high rate (93%) of predicting hearing losses greater than 32 dB while making no attempt to make finer discriminations. This more conservative approach minimizes serious predictive errors while identifying a high proportion of clinically significant hearing losses.

Acoustic Stimulation↗
PubMed1977

Methods for measuring the temporal characteristics and filter response of electroacoustic impedance instruments.

Methods for determining the temporal response of electroacoustic impedance instruments are presented along with sample measurements from one instrument. The conditions under which reflex artifacts may occur are discussed in light of electrical measurements of filter response characteristics and measurements of the "threshold" of the artifact measured from two subjects with no acoustic reflex.

Acoustic Stimulation↗
PubMed1977

Tympanometric asymmetry.

Tympanometric asymmetry was investigated in 17 normal adult subjects. Experimental variables included transmission quantity, probe frequency, direction of pressure change, and type of probe tip. Tympanograms were characterized by systematic asymmetries that appeared to be related predominantly to middle-ear effects, although ear canal effects probably contributed to the asymmetries as well. Implications for the standardization of measurement procedures are discussed.

Acoustic Impedance Tests↗
PubMed1977

Interactions among tympanometric variables.

To gain a better understanding of tympanometric results that have been difficult to interpret, such as asymmetrical and W-shaped tympanograms, acoustic susceptance and conductance tympanograms were measured from subjects with normal hearing and from subjects with well-defined middle ear pathology. Acoustic reactance, resistance, and impedance were computed and predicted from the measured data. Asymmetrical tympanograms derive in large part from the marked asymmetry in acoustic resistance as a function of ear canal pressure. W-shaped tympanograms result from interactions between reactance and resistance that occur when the two quantities assume similar absolute values or when reactance is mass controlled. A criterion for distinguishing between W-shaped tympanograms that are normal from those that are abnormal is discussed.

Acoustic Impedance Tests↗
PubMed1975

Static and dynamic acoustic impedance measurements in infant ears.

Tympanometry and acoustic reflex threshold data are reported for a series of presumable normal infants ranging in age from 55 to 132 days. In general, tympanograms displayed single peaks between +/- 50 mm H2O. Susceptance tympanograms with a 660-Hz probe frequency were sometimes characterized by monotonically increasing susceptance as ear canal pressure was changed from -200 to +200 mm H2O. Static values of acoustic conductance, susceptance, admittance, resistance, reactance, impedance, and phase angle were computed from tympanograms using the values of ambient and +200 mm H2O (0/+200 procedure) and maximum and minimum tympanometric values (MAX/MIN procedure). Comparison of the data from the two computational procedures suggested that the MAX/MIN procedure produces means and standard deviations of static values which are more manageable for establishing confidence limits with which to evaluate potentially pathological subjects. The MAX/MIN procedure resulted in lower mean values of conductance and susceptance for infant subjects relative to previously reported adult data using a similar computational procedure. Acoustic reflex thresholds were clearly present in all testable infants at coupler sound pressure levels similar to adult data, suggesting that the relations between reflex thresholds and hearing sensitivity demonstrated in adult subjects are similarly applicable to infant subjects. Mild sedation to induce sleep without altering the reflex would make acoustic reflex threshold measurement a useful procedure for screening large numbers of infants.

Adult↗
PubMed1975

The measurement of critical masking bands.

The characteristics of the critical masking band, that spectral region of a wideband noise that is effective in masking a pure-tone signal, were inferred by measuring detectability (d) for tonal signals as a function of the cutoff frequency of a low-pass or high-pass noise masker. As the cutoff frequency of a low-pass noise was decreased from the wide-band (100-7000 Hz) condition toward the signal frequency, (500, 1000, or 4000 Hz) dectability maintained a constant minimum until a further reduction in cutoff frequency increased detectability, presumably due to a reduction in masker power within the critical band. As cutoff frequency was reduced further, detectability increased monotonically until detection reached 100%. This usually occurred when the cutoff frequency is 0.04 to 0.06 octaves below the signal frequency. The range of cutoff frequencies over which detectability changes occurred defines the critical masking band. These ranges correspond closely to well-known critical ratio data. The dependence of d on noise cutoff frequency did not differ at the two signal levels (15 and 25 dB SL) used in this experiment. The critical band appeared symmetrical about the signal frequency for most subjects and most experimental conditions, although some subjects displayed a marked asymmetry in the high frequency direction for some conditions.

Acoustic Stimulation↗
PubMedDate not supplied

The effects of experimentally-produced middle ear lesions on tympanometry in cats.

Tympanometry was performed before and after producing specific lesions in the middle ears of cats. The lesions selected for study included stapes fixation, ossicular discontinuity, and scarred tympanic membranes. Stapes fixation resulted in marked increases in middle ear impedance, easily detected with tympanometry. Ossicular discontinuity resulted in complex tympanometric shapes which were easily accounted for by simple interactions between acoustic resistance and reactance. The complex shapes that occurred in normal and abnormal ears with pressure changing from negative to positive resulted from more complicated interactions. Large surgical incisions in the posterior-superior quadrant of the eardrum were quite visible at otoscopy but could not be detected tympanometrically one month after surgery.

Acoustic Impedance Tests↗
PubMedDate not supplied

Detection of hearing loss with ipsilateral acoustic reflex thresholds.

This study consisted of two experiments both of which involved measurement of the ipsilateral acoustic reflex threshold (ART). In Experiment I, ipsilateral ARTs were measured in normal-hearing adults for a 2 000-Hz tone and computer-generated complex stimuli of varying bandwidth. Results of this experiment revealed that the bandwidth effect for the ipsilateral ART was similar to the contralateral effect. The ART decreased monotonically as a function of bandwidth of the reflex-eliciting stimulus. Results of Experiment II indicated that ipsilateral ARTs successfully differentiated between normal hearing and significant hearing loss, in difficult-to-test groups of young children, when used with the bivariate plotting procedure. In addition, obtaining reflexes ipsilaterally, rather than contralaterally, appeared to have advantages with this population. The ipsilateral test apparatus is less cumbersome, the possibility of calibration error from a malpositioned contralateral earphone is eliminated and the children were generally more accepting of the ipsilateral assembly.

Adolescent↗
PubMedDate not supplied

Multifrequency tympanometry in chinchillas.

Multifrequency tympanometry (MFT), using probe frequencies ranging from 226-2,000 Hz, was performed on normal chinchillas to obtain normative data against which to compare results from animals with middle ear pathology. A series of validating experiments was conducted to determine the effects of anatomical alterations of the middle ear on MFT. These included artificially extending the ear canal, opening the bulla, injecting saline into the middle ear, and disrupting the ossicular chain. The results indicate that MFT characteristics of chinchilla ears are qualitatively similar to those observed in normal humans and patients with middle ear disease, and MFT provides information that is not available from the 226-Hz tympanogram.

Acoustic Impedance Tests↗