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Biomedical subjects

S Buus

Publications and source records attributed to S Buus.

120 records · Page 7Linked to original sources
PubMed1984

Temporal gap detection in sensorineural and simulated hearing impairments.

The objectives of this study were to assess the effect of the configuration of a hearing loss on gap detection and to determine if hearing impairment affects temporal resolution, per se. The minimum detectable gap duration, MDG, in a low-pass (cut-off at 7 kHz) noise was measured monaurally as a function of sound pressure level in six listeners with normal hearing, seven with hearing impairments of primarily cochlear origin, and eight with impairments simulated by masking. The impaired listeners' MDGs at 80 and 90 dB vary from about 3.5 ms (equal to the normal MDG) to about 8 ms and show little correlation with their average HL. At lower levels, the MDG is enlarged for all impaired listeners owing to the decreased SL of the noise. Most of the enlargement of the MDG could be reproduced by presenting a normal listener with a masking noise spectrally shaped to simulate the impaired listener's audiogram. However, at high levels, some impaired listeners performed worse than their simulated-loss counterparts, indicating that temporal resolution per se may be reduced in some, but not all, impaired listeners.

Adult↗
PubMed1984

Chloroquine inhibits accessory cell presentation of soluble natural and synthetic protein antigens.

We have studied the in vitro effect of the lysosomotrophic agent, chloroquine, on the presentation of soluble protein antigens by guinea pig accessory cells. Chloroquine inhibited the capacity of antigen-pulsed accessory cells to stimulate proliferation in appropriately primed T cells. The effect was time- and dose-dependent. A brief treatment solely of the accessory cells with the drug compromised their ability to stimulate primed T cells in a subsequent culture provided the accessory cells were treated with chloroquine before their exposure to the antigen. These results suggest that chloroquine acts on an early event in the antigen handling by accessory cells. Chloroquine is a well known inhibitor of lysosomal proteolysis, and it is likely that its effect on antigen presentation is caused by an inhibition of antigen degradation.

Animals↗
PubMed1984

Lateralization and frequency selectivity in normal and impaired hearing.

The onset-time difference delta T required to lateralize a 30-ms bifrequency tone burst toward the leading ear was measured as a function of the frequency difference delta F between the tone in the left ear and the tone in the right ear. At center frequencies of 0.5 and 4 kHz, four normal listeners tested at 80 and 100 dB SPL had delta Ts that were relatively constant at subcritical delta Fs, but increased at delta Fs wider than a critical band. At 1 kHz, delta T increased with delta F even at subcritical delta Fs. Ten listeners with cochlear impairments were tested at 100 dB SPL. Seven had normal delta Ts at 4 kHz, despite hearing losses between 50 and 70 dB. At 0.5 and 1 kHz, mildly impaired listeners had nearly normal lateralization functions, whereas more severely imparied listeners had very large delta Ts and no frequency selectivity. These and other findings indicate that listeners even with moderate to severe hearing losses can lateralize normally on the basis of interaural differences in onset envelope, but not on the basis of temporal differences in the fine structure.

Adolescent↗
PubMed1983

Competition of chemically related antigens for presentation by accessory cells to T cells requires expenditure of metabolic energy by the accessory cells.

The immune responsiveness of guinea pigs both to dinitrophenyl-poly-L-lysine (DNP-PLL) and to the lysine-rich random copolymer of L-glutamic acid and L-lysine (GL) is controlled by the 'poly-L-lysine gene'. We have previously demonstrated that accessory cells of responder strains can be made incapable of presenting DNP-PLL to responsive T cells in assays for proliferation, by in vitro exposure of the cells to GL before and during their exposure to DNP-PLL. We demonstrate here that the presence of anti-Ia antibody in the cultures does not interfere with the apparent competition of the two antigens for presentation by accessory cells. Furthermore, the two antigens do not compete for presentation when the accessory cells are exposed to them at 1 degree C, suggesting that endocytosis and/or other energy-requiring cellular events are necessary for the competition.

Animals↗
PubMed1983

Discrimination of envelope frequency.

Discrimination of envelope frequency was measured as the just noticeable increase in envelope frequency of monotic, 60-dB two-tone complexes at geometric center frequencies (CFs) of 500, 1000, 2000, and 4000 Hz. (The envelope frequency is equal to the frequency separation, delta F, between the two components.) At a given CF the jnds were approximately constant up to a critical envelope frequency between 10% and 20% of the CF, roughly equivalent to the critical band, beyond which they increased to a maximum at about 40% of the CF. Below the critical envelope frequency, the jnd increased with CF. Measurements at 40 dB SPL with and without masking of the aural distortion products showed that the influence of aural distortion is minimal. Additional measurements showed that at narrow frequency separations, discrimination was better for monotic two-tone complexes than for pure tones, three-tone complexes, and dichotic two-tone complexes. The results indicate that envelope frequency may serve as a cue for discrimination up to a frequency between 30% and 40% of the CF, although its effectiveness at high envelope frequencies is severely diminished by the auditory filter. A comparison with other data on envelope frequency discrimination indicates that the jnds' dependence on the envelope frequency may depend on how the slope of the temporal envelope varies with envelope frequency.

Adult↗
PubMed1982

The SISI test: a review. Part I.

This is the first of two papers reviewing the SISI test. Following a discussion of the history of clinical intensity discrimination tests, a large body of data on the SISI test is reviewed with special attention to its procedure, as well as its validity and reliability. The following conclusions are drawn: (1) Sufficient practice should be given prior to the onset of data collection. (2) The number of presentations can safely be reduced to 10 if the patient either responds consistently or does not respond at all. (3) SISI possesses good validity and reliability. Used in conjunction with other tests, it gives valuable diagnostic information.

Hearing Disorders↗
PubMed1982

The SISI test: a review. Part II.

This is the second of two papers reviewing the SISI test. In this paper we discuss modifications of SISI, and the effects of contralateral masking and tone decay. We also compare SISI to other psychoacoustic site of lesion tests and discuss the implications of the results obtained in SISI. The following conclusions are drawn: (1) SISI performed at high levels appears powerful in detecting retrocochlear impairments. (2) Contralateral masking is advisable when cross-hearing cues are present. The masking level should be minimized and a noise level 10 dB below the level of the contralaterilized tone provides sufficient masking. (3) SISI remains valid despite the presence of tone decay. (4) High SISI scores in cochlearly impaired listeners do not indicate improved auditory acuity.

Audiometry, Pure-Tone↗
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

Loudness of complex sounds as a function of the standard stimulus and the number of components.

The purpose of this study was twofold: to determine if the measured loudness level of a signal depends on the standard stimulus used and to measure loudness as a function of the number of components in a wide-band signal. The stimuli were a pure tone, tone complexes with frequency separations of 231 and 1592 Hz, and noise bands with widths of 220 and 1592 Hz. The center frequency was 1 kHz and the loudness level was approximately 65 phons. Loudness matches between all combinations of stimuli showed that the measured loudness of the sounds did not depend on the standard stimulus used and the measured loudness level of a wide-band sound increased as a function of the number of components. Individual observers were consistent in their loudness estimations; the greatest source of variability was among subjects. Additional measurements indicated that the rate at which loudness increased beyond the critical band appeared to be greater for noise bands that for two-tone complexes.

Acoustic Stimulation↗
PubMedDate not supplied

Structural characteristics of an antigen required for its interaction with Ia and recognition by T cells.

A detailed analysis of the residues within an immunogenic peptide that endow it with the capacity to interact with Ia and to be recognized by T cells is presented. Ia interacts with only a few of the peptide residues and overall exhibits a very broad specificity. Some residues appear to interact both with Ia and with T cells, leading to a model in which a peptide antigen is 'sandwiched' between Ia and the T-cell receptor.

Amino Acid Sequence↗
PubMedDate not supplied

Toward a clinical procedure for narrowband gap detection I: a psychophysical procedure.

This paper examines a possible procedure for a clinical gap-detection test that is simple, frequency specific, and reliable. A cued yes-no method of maximum likelihood (MML) procedure was compared to an up-down three-interval, two-alternative, forced-choice procedure. Results from five trained and seven naive listeners indicate that the yes-no MML procedure yields valid and efficient estimates of narrowband gap-detection thresholds. Preliminary tests yield encouraging results.

Adult↗