Biomedical subjects

A Sek

Publications and source records attributed to A Sek.

22 records · Page 2Linked to original sources

PubMed1992

Detection of combined frequency and amplitude modulation.

This article is concerned with the detection of mixed modulation (MM), i.e., simultaneously occurring amplitude modulation (AM) and frequency modulation (FM). In experiment 1, an adaptive two-alternative forced-choice task was used to determine thresholds for detecting AM alone. Then, thresholds for detecting FM were determined for stimuli which had a fixed amount of AM in the signal interval only. The amount of AM was always less than the threshold for detecting AM alone. The FM thresholds depended significantly on the magnitude of the coexisting AM. For low modulation rates (4, 16, and 64 Hz), the FM thresholds did not depend significantly on the relative phase of modulation for the FM and AM. For a high modulation rate (256 Hz) strong effects of modulator phase were observed. These phase effects are as predicted by the model proposed by Hartmann and Hnath [Acustica 50, 297-312 (1982)], which assumes that detection of modulation at modulation frequencies higher than the critical modulation frequency is based on detection of the lower sideband in the modulated signal's spectrum. In the second experiment, psychometric functions were measured for the detection of AM alone and FM alone, using modulation rates of 4 and 16 Hz. Results showed that, for each type of modulation, d' is approximately a linear function of the square of the modulation index. Application of this finding to the results of experiment 1 suggested that, at low modulation rates, FM and AM are not detected by completely independent mechanisms. In the third experiment, psychometric functions were again measured for the detection of AM alone and FM alone, using a 10-Hz modulation rate. Detectability was then measured for combined AM and FM, with modulation depths selected so that each type of modulation would be equally detectable if presented alone. Significant effects of relative modulator phase were found when detectability was relatively high. These effects were not correctly predicted by either a single-band excitation-pattern model or a multiple-band excitation-pattern model. However, the detectability of the combined AM and FM was better than would be predicted if the two types of modulation were coded completely independently.

Adult↗

PubMed1987

Perception of amplitude and frequency modulated signals (mixed modulation).

This article discusses the detection of mixed modulation, i.e., simultaneous amplitude and frequency modulation (MM). The investigations have incorporated both a sine wave modulating signal and an irregular modulating signal, a very narrow noise band, of a specified center frequency. The results revealed that for a sinusoidal low-frequency modulating signal, amplitude and frequency changes that were separately subthreshold could be detected by listeners in mixed modulation. This indicates summation of sensations caused by simultaneous AM and FM modulation. This effect was not observed in the case of the irregular modulating signal. A hypothesis is advanced that the perception of modulated signals is governed by two mechanisms, viz., temporal and spectral. The operation of the two mechanisms depends mainly on the modulating frequency. The type of modulation does not play any significant role in this case.

Acoustic Stimulation↗

PubMedDate not supplied

Level of malondialdehyde after short-time omeprazole administration.

BACKGROUND: Omeprazole is a proton pump inhibitor of increasingly wide application in the treatment of different gastroenterological diseases. The purpose of the study was to evaluate the effect of omeprazole (O) on the level of plasma malondialdehyde (MDA). MATERIAL AND METHODS: Omeprazole was administered intraperitoneally to male Wistar rats twice a day, for 3 days, in two doses: O1-0.57 mg/kg body weight (b.w.), O2-5.71 mg/kg b.w. Twelve hours after the last injection half of the animals were terminated (I). The remaining rats were kept for the next 6 weeks without any xenobiotics (II). The blood was taken from the still beating heart and then centrifuged. The plasma level of MDA was determined and compared to the 1 mg of the blood protein. RESULTS: A significant (p < 0.05) increase of MDA level was found in the O2II group, as compared with the O2I group. The level of MDA was higher after 6 weeks' period in relation to the animals that were terminated on the 4th day of the experiment. CONCLUSION: Three-day omeprazole administration did not change the MDA level in the rat plasma.

Animals↗

PubMedDate not supplied

The effect of repeated administration of insulin on pain threshold and gamma-aminobutyric acid level in mouse brain.

In experiments on male Albino-Swiss mice weighing 18-22 g insulin given in doses of 2 i.u./kg caused no change in the time of reaction to pain, while the same dose administered daily for 7 days potentiated the analgesic action of morphine (3 mg/kg s.c.). Glucose caused no change in this effect of insulin. After 14 days of insulin treatment the time of reaction to pain in the animals subjected to the action of morphine returned to its initial value. Twenty-four hours after the last administration of morphine the level of gamma-aminobutyric acid (GABA) was found to be decreased in the animals receiving insulin with glucose. These results suggest that the central action of insulin is dependent not only on hypoglycaemia produced by it, but may be due also to its direct action on the central structures and an indirect action mediated by its effect on other neurotransmitter systems.

Animals↗