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Biomedical subjects

A Y Supin

Publications and source records attributed to A Y Supin.

15 recordsLinked to original sources
PubMed2001

The effect of masking noise on rippled-spectrum resolution.

Ripple-density resolution in a rippled sound spectrum (probe band) under the effect of another band (masker) was studied in normal listeners. The resolvable ripple density in the probe band was measured using a phase-reversal test. The principle of the test was to find the highest ripple density at which an interchange of mutual peak and valley position (the ripple phase reversal) was detectable. Probe bands were 0.5 octave (oct) wide with center frequencies of 1, 2, and 4 kHz. When a masker band was below the probe one (a low-frequency masker), it markedly reduced the ripple-density resolution. The effect of the low-frequency masker enhanced (ripple-density resolution decreased) with decreasing the stop-band (frequency spacing) between the probe and masker bands. The strongest masker effect was observed at zero spacing between the probe and masker bands. However, when the probe band overlapped the masker one so that no masker power was below the probe band, the masker effect diminished (ripple-density resolution partially released). Increase of the masker bandwidth above 0.5 oct by shifting its lower boundary downwards did not enhance the masker effect. Masker bands above the probe one (high-frequency maskers) did not influence the ripple-density resolution.

Acoustic Stimulation↗
PubMed2001

Contribution of various frequency bands to ABR in dolphins.

Auditory brainstem responses (ABR) to clicks and noise bursts of various frequency bands and intensities were recorded in two bottlenosed dolphins, Tursiops truncatus. The purpose was to assess contributions of various parts of the cochlear partition to ABR and travelling wave velocity in the cochlea. At band-pass filtered stimuli (1-0.25 oct wide), ABR amplitude increased with increasing stimulus frequency, thus indicating higher contribution of basal cochlear parts. At high-pass and low-pass filtered stimuli, ABR amplitude increased with passband widening. However, the sum of all narrow-band contributions was a waveform of higher amplitude than the real ABR evoked by the wide-band stimulus. Applying a correction based on an assumption that the 'internal spectrum' is about 0.4 oct wider than the nominal stimulus spectrum resulted in the sum of narrow-band contributions equal to the wide-band ABR. The travelling wave velocity was computed based on ABR latencies and assigned a frequency of 128 kHz to the basal end of the cochlea. The computation gave values from 38.2 oct/ms at the proximal end of the basilar membrane to 4.0 oct/ms at a distance of 3.25 oct (13.5 kHz).

Acoustic Stimulation↗
PubMed2000

Ganglion cells density and retinal resolution in the sea otter, Enhydra lutris.

The topographic distribution, density, and size of ganglion cells were studied in retinal wholemounts of the sea otter, Enhydra lutris. The cell distribution showed a well defined horizontal streak of higher cell density, and within this streak, a narrow area of the highest cell density. The peak cell density in this area ranged from 4050 to 4400 cells/mm(2), with a mean of 4225 cells/mm(2). The ganglion cell size ranged from 7 microm to 47 microm but the majority of cells were 7 to 30 microm. Cell size distribution revealed three size groups: 7-16, 17-28, and 29-47 microm. The highest-density area contained mainly small (7-16 microm) cells. The cell-density data predict a retinal resolution around 7' in water. Retinal organization in the sea otter exhibits more properties common with terrestrial rather than aquatic mammals, both in terms of ganglion cell characteristics and in terms of their topographic distribution.

Animals↗
PubMed1998

Auditory evoked responses to rhythmic sound pulses in dolphins.

The ability of auditory evoked potentials to follow sound pulse (click or pip) rate was studied in bottlenosed dolphins. Sound pulses were presented in 20-ms rhythmic trains separated by 80-ms pauses. Rhythmic click or pip trains evoked a quasi-sustained response consisting of a sequence of auditory brainstem responses. This was designated as the rate-following response. Rate following response peak-to-peak amplitude dependence on sound pulse rate was almost flat up to 200 s-1, then displayed a few peaks and valleys superimposed on a low-pass filtering function with a cut-off frequency of 1700 s-1 at a 0.1-amplitude level. Peaks and valleys of the function corresponded to the pattern of the single auditory brain stem response spectrum; the low-pass cut-off frequency was below the auditory brain stem response spectrum bandwidth. Rate-following response frequency composition (magnitudes of the fundamental and harmonics) corresponded to the auditory brain stem response frequency spectrum except for lower fundamental magnitudes at frequencies above 1700 Hz. These regularities were similar for both click and pip trains. The rate-following response to steady-state rhythmic stimulation was similar to the rate-following response evoked by short trains except for a slight amplitude decrease with the rate increase above 10 s-1. The latter effect is attributed to a long-term rate-dependent adaptation in conditions of the steady-state pulse stimulation.

Acoustic Stimulation↗
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↗
PubMed1994

Rotational swimming tendencies in the dolphin (Tursiops truncatus).

Anecdotal evidence suggests that dolphins placed in a pool exhibit stereotypic swimming in circles. The present study confirmed these observations in a sample of thirteen dolphins. The majority of dolphins (84.6%) showed highly consistent directional swimming in counterclockwise circles. The latter directionality held throughout the circadian cycle and resisted environmental manipulations. Only social interaction was capable of altering the directionality of circumnavigation. The consistency of unidirectional swimming is considered paradoxical in view of the existing evidence regarding the alternating of hemispheric activity in sleeping dolphins.

Animals↗
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↗
PubMed1992

Peak density, size and regional distribution of ganglion cells in the retina of the fur seal Callorhinus ursinus.

The total number, size, topographic distribution and peak density of ganglion cells were studied in retinal wholemounts of the fur seal, Callorhinus ursinus. The cell distribution showed a distinct zone of high ganglion cell density. It was located in the temporal retinal quadrant, near the horizontal meridian, 10-12 mm (25-31 degrees) from the optic disk. The peak cell density in this zone was 812-1332 cells/mm2 (mean 1053 cells/mm2), i.e. 125-205 cells/deg2 (mean 162 cells/deg2). These data predict a retinal resolution of 5.6-7.1 cycle/deg. The ganglion cell soma size ranged from 10 to 50 microns. Cell size histograms were bimodal in shape with modes below and above 30 microns.

Animals↗
PubMed1990

Location of an acoustic window in dolphins.

Auditory brainstem responses (ABR) to sound clicks from sources in different positions were recorded in dolphins Inia geoffrensis. The position of the acoustic window was determined by measurement of acoustic delays. The acoustic window was found to lie close to the auditory meatus and the bulla rather than on the lower jaw.

Animals↗