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Biomedical subjects

V V Popov

Publications and source records attributed to V V Popov.

At least 37 records · Page 2Linked to original sources
PubMed1998

Lateral suppression of rhythmic evoked responses in the dolphin's auditory system.

In the auditory system of bottlenose dolphins (Tursiops truncatus), a brain-evoked response to rhythmic sound amplitude modulations (the envelope-following response) was markedly suppressed by addition of another sound with a frequency 5-20 kHz higher and an intensity down to 40 dB lower than that of the amplitude-modulated signal. This effect was called paradoxical lateral suppression. This phenomenon was primarily observed when the amplitude-modulated stimulus had a carrier frequency above 30 kHz and modulation rates above 500 Hz. Only the sustained rhythmic response was suppressed, while the transient on-response was not. This indicates that the suppression influenced the ability of evoked potentials to follow rapid amplitude modulations. This prevents weak sounds from being masked by stronger ones.

Acoustic Stimulation↗
PubMed1998

Ripple density resolution for various rippled-noise patterns.

Ripple-density resolution was measured in normal humans using rippled noise with a phase-reversal test. The principle of the test was to find the highest ripple density at which an interchange of spectral peak and trough positions (the phase reversal) is detectable. Different rippled noise patterns were used: (i) either frequency-proportional or constant ripple spacing; (ii) various bandwidth; and (iii) either steep or shallow slopes of the spectrum envelope. When tested with frequency-proportional rippled noise, ripple-density resolution as expressed in relative units (the center frequency to ripple spacing ratio) little depended on frequency within a range of 1 to 8 kHz: from 11.4 at 1 kHz to 14.9 at 8 kHz, mean 13.1. These values were virtually independent on noise bandwidth. When tested with constant ripple spacing, the resolution was of similar values taking the relative ripple density at the lower part of the passband. Being measured by noise with steep spectral edges, the resolution was five units higher than it was for shallow-enveloped spectra, thus suggesting some edge effects at the spectrum boundaries. The resolution values obtained were about twice higher than those predicted by peripheral auditory filter tuning.

Adult↗
PubMed1998

[Development of the device for Japanese quail nestlings maintenance in microgravity].

Postembryonic development of the nestlings in microgravity has revealed their capacity for orientation and stabilization of their position in space which called for developing the special devices. Under terrestrial laboratory conditions the facility for maintaining the nestlings aged up to 10 days has been developed and tested. The results of tests have indicated that despite the restricted volume of individual cages the nestlings can grow without significant variations from the norm as evidenced by the dynamics of nestlings body mass during 10 days and the amount of consumed food.

Animals↗
PubMed1997

Paradoxical lateral suppression in the dolphin's auditory system: weak sounds suppress response to strong sounds.

A paradoxical phenomenon was found in the auditory system of dolphins: weak sounds suppressed the brain responses to much stronger sounds. This occurred when the brain evoked potentials to rhythmic sound amplitude modulations were recorded. The response was markedly suppressed by addition of another sound of higher frequency and down to 40 dB lower intensity than the amplitude-modulated signal. Only the sustained rhythmic response was suppressed while transient on-response was not, thus indicating that the suppression influenced the ability of evoked potentials to follow rapid amplitude modulations. This prevents weak sounds from being masked by stronger ones. It may help a dolphin to perceive weaker echo-signals in the background of stronger emitted pulses.

Acoustic Stimulation↗
PubMed1997

Frequency-temporal resolution of hearing measured by rippled noise.

Frequency-temporal resolution of hearing was measured in normal hearers using rippled noise stimulation in conjunction with a phase-reversal test. The principle of the test was to interchange peak and trough positions (the phase reversal) and to find the highest ripple density at which such interchange is detectable depending on reversal rate. The measurements were made using narrow-band noises with center frequencies of 0.5-4 kHz. The ripple-density resolution limits were constant at phase-reversal rates below 2-3/s and diminished at higher phase-reversal rates. A model is proposed to explain the data based on the envelope fluctuations inherent in noise; these fluctuations are supposed to limit detection of frequency-temporal sound patterns.

Acoustic Stimulation↗
PubMed1997

Detection of temporal gaps in noise in dolphins: evoked-potential study.

Temporal resolution of hearing was studied in bottlenosed dolphins by recording the auditory brain-stem response (ABR) evoked by gap in noise. Gaps shorter than 0.5 ms evoked a response combining both off- and on-components; longer gaps evoked separate off- and on-responses. Both the response to a short gap and on-response to the end of a long gap increased with increasing gap duration. On-response recovered completely at gap duration of 5-10 ms. Small but detectable response arose at gap duration as short as 0.1 ms. Contrary to the on-response after a long silence, the response to a short gap was less dependent on noise intensity. From these data, the temporal transfer function of the supposed integrator was derived assuming nonlinear transform of the integrator output to ABR amplitude. Equivalent rectangular duration of the found temporal transfer function was 0.27 ms.

Animals↗
PubMed1997

Frequency tuning of the dolphin's hearing as revealed by auditory brain-stem response with notch-noise masking.

Notch-noise masking was used to measure frequency tuning in a dolphin (Tursiops truncatus) in a simultaneous-masking paradigm in conjunction with auditory brain-stem evoked potential recording. Measurements were made at probe frequencies of 64, 76, 90, and 108 kHz. The data were analyzed by fitting the rounded-exponent model of the auditory filters to the experimental data. The fitting parameter values corresponded to the filter tuning as follows: QER (center frequency divided by equivalent rectangular bandwidths) of 35 to 36.5 and Q10 dB of 18 to 19 at all tested frequencies.

Acoustic Stimulation↗
PubMed1996

Frequency tuning curves of the dolphin's hearing: envelope-following response study.

Simultaneous tone-tone masking in conjunction with the envelope-following response (EFR) recording was used to obtain tuning curves in dolphins (Tursiops truncatus). The EFR was evoked by amplitude-modulated probes of various frequencies. A modulation rate of 600 Hz was found to fit the requirement to have a narrow spectrum and evoke EFR of large amplitude. Tuning curves were obtained within the frequency range from 11.2 to 110 kHz. The Q10 values of the obtained tuning curves varied from 12-14 at the 11.2 kHz center frequency to 17-20 at the 64-90 kHz frequencies.

Acoustic Stimulation↗
PubMed1995

Envelope-following response and modulation transfer function in the dolphin's auditory system.

Potentials following the envelopes of sinusoidally amplitude-modulated tones (envelope response, EFR) were recorded from the head surface in bottle-nosed dolphins. EFR appeared at modulation rates from 300 to 3400 Hz. EFR amplitude was higher at rates from 500 to 1400 Hz with peaks at 600 and 1000 Hz and troughs at 700-850, 1200, and 2000 Hz; at rates above 1700 Hz it fell steeply. EFR dependence on modulation depth was linear except at the highest response amplitudes, which made it possible to obtain the modulation transfer function (MTF). EFR appears to be generated by several sources. One source had a latency of about 4 ms and followed modulation rates up to 1700 Hz, while another had a latency of 2 ms and followed modulation rates up to 3.4 kHz. The latencies of both sources coincided with those of waves of the auditory brainstem response (ABR). Comparison of MTF with the ABR spectrum had shown that several MTF peaks and troughs reflected the ABR spectrum. The latencies of the two sources were consistent with origins in the midbrain and auditory nerve, respectively.

Acoustic Stimulation↗
PubMed1995

Temporal resolution in the dolphin's auditory system revealed by double-click evoked potential study.

Temporal resolution of hearing in two bottlenosed dolphins was estimated by measuring auditory brain-stem response (ABR) recovery in conditions of double-click stimuli. From these data, temporal transfer function of the supposed integrator was derived assuming nonlinear transform of the integrator output to ABR amplitude. The obtained temporal transfer function showed a nearly constant level up to 200 microseconds. then decay to approximately -3 dB at 300 microseconds (as presented in the sound intensity domain), and subsequent decay of 10-11 dB per time doubling (about 35 dB/decade).

Animals↗
PubMed1994

Frequency resolving power of the human's hearing.

Frequency resolving power (FRP) of the human's hearing was measured using the rippled noise as a probe. To examine the ripple discrimination, a phase-reversal test was used: the rippled noise was replaced by that with the opposite peak and through positions. This switch can be detected only when rippled structure of the noise spectrum is discriminated. The highest ripple density when the switch was detectable was taken as a FRP measure. Narrow-band rippled spectra were used to measure the FRP within a frequency range of 0.175 to 11 kHz. The highest resolvable ripple density in absolute measure (ripples number per kHz) was about 21/kHz at frequencies below 0.5 kHz and fell down at higher frequencies. Resolvable ripple density in relative measure (central frequency divided by ripple spacing) was about 22 relative units at frequencies above 2.8 kHz and fell down at lower frequencies.

Acoustic Stimulation↗
PubMed1994

Frequency resolving power measured by rippled noise.

Frequency resolving power (FRP) was measured in normal humans using rippled noise with a phase-reversal test. The principle of the test was to find the highest ripple density at which an interchange of mutual peak and trough position (the phase reversal) in the rippled spectrum is detectable. In the frequency range below 0.5 kHz FRP was found to be about 21 ripples per kHz when tested by both broad-band and narrow-band rippled noise. In the frequency range above 2 kHz, FRP measured by the narrow-band rippled noise was 22 to 23 relative units (relation of the noise central frequency to the ripple frequency spacing).

Acoustic Stimulation↗
PubMed1993

ABR frequency tuning curves in dolphins.

Tone-tone masking was used to determine auditory brain-stem response tuning curves in dolphins (Tursiops truncatus) in a simultaneous-masking paradigm. The Q10 of the curves was as large as 16-19 in the frequency range 64-128 kHz. In the range 45-16 kHz, Q10 decreased proportionally to the frequency with the bandwidth of the curves being constant, about 3.5-4 kHz at the 10-dB level. Tuning curves below 45 kHz are supposed to reflect broad spectral bandwidth of the probe's effective part which is no longer than 0.5 ms, irrespective of actual probe duration. Tuning curves above 64 kHz are supposed to reflect the real frequency tuning of the dolphin's auditory system.

Acoustic Stimulation↗