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PubMed1992

Effect of signal frequency and masker level on the frequency regions responsible for the overshoot effect.

Two experiments investigated the relative influence of components close to and remote from the signal frequency (fs) on the overshoot effect. Overshoot was defined as the difference in threshold between a signal presented 4 ms after, and that for one presented 300 ms after, the onset of a 350-ms masker. Experiment 1 measured the overshoot effect using both wideband and narrow-band maskers (centered on fs), at two signal frequencies and three masker levels. Experiment 2 used a masker consisting of a "middle band" (MB, centered on fs) and two flanking bands (FBs, which, when combined with the MB, produced a flat wideband spectrum). The masker was continuous except for a 300-ms interval just prior to the signal, during which either all three bands, the MB alone, or the FBs alone were turned off. The results of both experiments showed that the overshoot effect was usually determined by off-frequency components. However, the on-frequency components played a substantial role when signal-to-noise ratios (SNRs) at threshold were unusually high, such as at fs = 6500 Hz and intermediate masker levels. It is suggested that two different mechanisms contribute to the overshoot effect: an off-frequency mechanism which operates at all fs and masker levels, and an on-frequency mechanism which contributes to the overshoot effect only at high-threshold SNRs.

Attention↗

PubMed1997

The perception of frequency peaks and troughs in wide frequency modulations. IV. Effects of modulation waveform.

This work extends previous studies on the perceptual asymmetry between the local maxima and minima of wide frequency modulations (FMs) [L. Demany and K. I. McAnally, J. Acoust. Soc. Am. 96, 706-715 (1994); L. Demany and S. Clément, J. Acoust. Soc. Am. 97, 2454-2459 (1995); L. Demany and S. Clément, J. Acoust. Soc. Am. 98, 2515-2523 (1995)]. In experiment 1, subjects had to discriminate frequency shifts in the temporally central vertex of V- and A-shaped FMs imposed on 200-ms sinusoidal tone bursts. The precise shapes of these FMs varied in eight steps from quasi-triangles (with a durationless central vertex) to quasi-squares (with a long-duration central vertex). The central vertex was either a minimum or a maximum, but in each case the corresponding frequency was near 1000 Hz and the FM span was about 0.5 oct. For each FM shape, the discrimination threshold was lower when the vertex was a maximum than when it was a minimum, but (in four subjects out of five) this difference decreased monotonically as the FM became less and less triangular. FM shape had a remarkably small effect on the discrimination of the maxima, and the thresholds measured for the sharpest maxima were unexpectedly low. In subsequent experiments, subjects had to discriminate frequency shifts in the starting point or the final point of unidirectional FMs (tone glides) that spanned about 0.5 oct in 100 ms. The relevant frequency extremum was near 1000 Hz in each condition. At the final point of the glides, discrimination was better for rising glides than for falling glides. At the starting point of the glides, discrimination was better for falling glides than for rising glides. Thus discrimination was always better when the relevant frequency extremum was a maximum than when it was a minimum, and this effect was produced both "forward" and "backward." The latter fact suggests that the perceptual asymmetry of FM originates at least partly from central factors.

Differential Threshold↗

PubMed2000

Extracting spectral envelopes: formant frequency matching between sounds on different and modulated fundamental frequencies.

The four experiments reported here measure listeners' accuracy and consistency in adjusting a formant frequency of one- or two-formant complex sounds to match the timbre of a target sound. By presenting the target and the adjustable sound on different fundamental frequencies, listeners are prevented from performing the task by comparing the absolute or relative levels of resolved spectral components. Experiment 1 uses two-formant vowellike sounds. When the two sounds have the same F0, the variability of matches (within-subject standard deviation) for either the first or the second formant is around 1%-3%, which is comparable to existing data on formant frequency discrimination thresholds. With a difference in F0, variability increases to around 8% for first-formant matches, but to only about 4% for second-formant matches. Experiment 2 uses sounds with a single formant at 1100 or 1200 Hz with both sounds on either low or high fundamental frequencies. The increase in variability produced by a difference in F0 is greater for high F0's (where the harmonics close to the formant peak are resolved) than it is for low F0's (where they are unresolved). Listeners also showed systematic errors in their mean matches to sounds with different high F0's. The direction of the systematic errors was towards the most intense harmonic. Experiments 3 and 4 showed that introduction of a vibratolike frequency modulation (FM) on F0 reduces the variability of matches, but does not reduce the systematic error. The experiments demonstrate, for the specific frequencies and FM used, that there is a perceptual cost to interpolating a spectral envelope across resolved harmonics.

Auditory Perception↗

PubMed1987

Spatial frequency discrimination for sinewave gratings with random, bandpass frequency modulation: evidence for averaging in spatial acuity.

Spatial frequency difference thresholds for vertical, high contrast sinewave gratings were estimated at 1.25, 2.5, 5.0 and 10.0 cyc deg-1. Within an experiment two independent manipulations of the stimulus were employed: (1) the number of cycles of the sinewave grating was varied over a range of 2.0 to 15.0 cycles; and (2) a stationary, random frequency modulation was imposed on the sinewave. The probability density function of the frequency modulation was a Gaussian whose dispersion coefficient was varied, in different experiments, in the range of 0 to 10% of the frequency of the parent sinewave. Both of these experimental variables were found to affect the precision with which spatial frequency discrimination could be performed. The Weber fraction increased both as the number of cycles present was decreased and as the dispersion coefficient of the modulating function was increased. These two effects were independent. The data support previous psychophysical findings that spatial frequency discrimination involves averaging over the total area of the stimulus and are compatible with spatial primitive models of spatial contrast vision. The data are not compatible with those of Hirsch and Hylton (J. opt. Soc. Am. 72, 1367-1374) which suggest that spatial interval discrimination occurs solely by operation of foveal mechanisms.

Adult↗

PubMed2004

Diode-laser frequency stabilization by two-frequency Doppler-broadened absorption spectroscopy.

We demonstrate a robust method for frequency stabilization of a diode laser by two Doppler-broadened absorption spectra of the cesium D2 line. This technique employs an acousto-optical modulator to generate another frequency component from a diode laser to perform the spectroscopy. The 852-nm diode laser with frequency stabilization at the zero crossing of the error signal showed a peak-to-peak fluctuation of 800 kHz compared with a frequency-stabilized femtosecond laser over a 2-h period. This frequency-locking method is free of modulation and can be applied to frequency discriminators as well as to atomic resonances.

Journal Article↗

PubMed2005

Three-longitudinal-mode He-Ne laser frequency stabilized at 633 nm by thermal phase locking of the secondary beat frequency.

We present a simple scheme for thermal frequency stabilization of a three-longitudinal-mode He-Ne laser at 633 nm with improved short-term (5 x 10(-11) at 1-s average time) and long-term (124-kHz standard deviation for 10 h) frequency stability. A stabilized output power of 3 mW was readily obtained from the central mode by polarization-mode selection. The optical frequency of the central mode could be precisely tuned by an external frequency reference over 160 MHz with high precision or could be optically phase locked to a reference laser by use of a thermal frequency-stabilization circuit and an external acousto-optic modulator. The laser will be useful in various applications for which a laser source with high power and frequency stability is necessary.

Journal Article↗

PubMed2005

Suppression of nonlinear frequency sweep in an optical frequency-domain reflectometer by use of Hilbert transformation.

A compensation technique for reducing the effect of nonlinear optical frequency swept in an optical frequency-domain reflectometer (OFDR) is proposed. The instantaneous sweep optical frequency of an OFDR laser source is directly obtained by analysis of the interference signal from an auxiliary interferometer with a Hilbert transformation. Beating OFDR data from a main interferometer are regenerated with respect to the measured instantaneous optical frequency. We show that this technique dramatically improves the spatial resolution of a conventional OFDR and can be applied to an optical frequency-domain medical imaging system to eliminate the problem of a nonlinear frequency sweep effect.

Journal Article↗

PubMed2004

Optical clockwork with an offset-free difference-frequency comb: accuracy of sum- and difference-frequency generation.

We demonstrate a simple optical clockwork mechanism based on the broadened frequency comb of a femtosecond laser and on difference-frequency generation (DFG) in a nonlinear crystal. The DFG comb possesses a vanishing carrier envelope offset frequency that permits the construction of a simple and thus potentially more stable optical clockwork. In addition it offers the possibility of extending the frequency comb into the infrared spectral region. The overall accuracy and stability of the DFG comb relative to the initial frequency comb were measured to be 6.6 x 10(-21) and 10(-18) tau(-1), respectively, where tau is the averaging time in seconds. Assuming that sum- and difference-frequency generation are independent processes, our measurements suggest a <10(-20) accuracy for them.

Journal Article↗

PubMed2004

Absolute-frequency measurements with a stabilized near-infrared optical frequency comb from a Cr:forsterite laser.

A frequency comb is generated with a chromium-doped forsterite femtosecond laser, spectrally broadened in a dispersion-shifted highly nonlinear fiber, and stabilized. The resultant evenly spaced comb of frequencies ranges from 1.1 to beyond 1.8 microm. The frequency comb was referenced simultaneously to the National Institute of Standards and Technology's optical frequency standard based on neutral calcium and to a hydrogen maser that is calibrated by a cesium atomic fountain clock. With this comb we measured two frequency references in the telecommunications band: one half of the frequency of the d/f crossover transition in 87Rb at 780 nm, and the methane v2 + 2v3 R(8) line at 1315 nm.

Journal Article↗

PubMed2003

[Analysis of the frequency components of CR portal images and application to multi-objective frequency processing].

The image contrast of portal images obtained using computed radiography (CR) is low for radiation therapy, and their noise level is high. In order to improve the image quality of CR portal images, we investigated the relationship between the frequency components of the bone edge and noise area. We used a personal computer, conventional flatbed scanner, and public-domain software (NIH Image). To analyze the frequency components of bone edges, we generated difference images from the original and unsharp mask images of various sizes. In addition, we analyzed the frequency components of noise, after changing the cut-off frequency on the power spectrum to process a low- and high-pass filter. We found that the frequency components of bone edges and noise areas ranged from 0.18 to 0.25 cycle/mm and 1.30 cycles/mm, respectively. We conclude that this process can remove noise from homogeneous areas and preserve bone edges using multi-objective frequency processing.

Bone and Bones↗

PubMed1978

[The mathematical rationale for the clinical EEG-frequency-bands. 1. Factor analysis with EEG-power estimations for determining frequency bands].

In order to determine whether the clinically used frequency bands of the EEG can also be obtained by a mathematical system we did a factor analysis with 480 EEG recordings, 5 minutes each, in 60 healthy male volunteers. A power spectrum analysis was done and 57 frequency bands between 1.5 and 30.0 Hz in a half Hz steps were calculated. The factor structure obtained made the following frequency bands (Hz) reasonable: deltaF = 1.5 - 6.0, thetaF = 6.0 - 8.5, alpha1F = 8.5 - 10.5, alpha2F = 10.5 - 12.5, beta1F = 12.5 - 18.5, beta2F = 18.2 - 21.0, beta3F = 21.0 - 30.0. Except for alpha1F all other 6 frequency bands were represented by one general factor with the complexity 1. The variance of the alpha1F band is explained by several of the 6 factors. The clinically known and the by factor analysis obtained frequency bands in the beta-range are similar. The clinically alpha-band is subdivided into two frequency bands alpha1F and alpha2F by the factor analysis. The clinically known border line between delta- and theta-band of 3.5 Hz cannot be found by factor analysis.

Adult↗

PubMed1975

[Tumor frequency in autopsy cases. I: frequency, age and sex distribution, primary localization (author's transl)].

The analysis is based on the catalogue of neoplasms notifiable in the German Democratic Republic (ICD-Code Nrs. 140-209, 210.2, 211.3, 211.9, 225, 226.2, 226.3, 253.0, 253.2, 702, 757.2). At the Medical Academy of Erfurt 22,155 autopsies (12,212 males, 9,943 females) of adults (15 years and upwards) were registrated in the period from 1950 to 1966. 7,533 malignant tumours (34.2%) were observed. 99 cases were eliminated because of an unknown localization of the primary tumour. The remaining 7,442 cases (33.6%) are distributed among 3,987 males (326% of males) and 3,455 females (34,7% of females). The frequency difference based on the autopsy frequency of males or females, is distinct. Malignant epithelial tumours were observed in 5,559 cases (253% of autopsies; 752% of malignant tumours); 2,945 males and 2,654 females. The frequency difference also is distinct. Malignant nonepithelial tumours were observed in 1,843 cases (83% of autopsies, 24.8% of malignant tumours); 1,042 males and 801 females. There is no difference in frequency. Age and sex distribution as well as the relative curve of age distribution (Dormanns 1933) are presented for all the tumours, epithelial and nonepithelial neoplasms. The frequency of primary tumour-localization is reported for males and females, too. In males the frequency is in the following order: lung, stomach, hemopoetic-lymphatic system, colon and central nervous system; in females: sex organs (without mamma), stomach, colon, hemopoetic-lymphatic system and central nervous system.

Adolescent↗

PubMed1991

Rise time and center-frequency effects on auditory brainstem responses to high-frequency tone bursts.

The effects of rise time and center frequency on the auditory brainstem response (ABR) elicited by high-frequency tone bursts were examined in six normal-hearing adults. Tone bursts with rise times of 0.1, 0.25, 0.5, and 1.0 msec, duration of 2 msec, and center frequencies of 8, 10, and 12 kHz were used in this study. The absolute latencies of waves I, III, and V were obtained in all subjects, and interpeak intervals of I-III, III-V, and I-V were calculated. As would be expected, rise time significantly affected the absolute latencies of waves I, III, and V, i.e., faster rise times shortened the absolute latencies, but did not affect the interpeak latencies. The tone-burst frequency significantly affected the latency of wave I but not the later waves. No significant differences were found in reliability of the response at different rise times or frequencies, within or across sessions. An estimate of the effective bandwidth of the stimulus suggests that frequency specificity of the response is maintained with fast rise time tone-burst stimuli.

Acoustic Stimulation↗

PubMed1993

Analysis of a Danish Caucasian population sample of single locus DNA-profiles. Allele frequencies, frequencies of DNA-profiles and heterozygosity.

The frequency distributions of the length of restriction fragments (HinfI) revealed by RFLP-analysis (restriction fragment length polymorphism) of blood samples from 482 Danish Caucasians using the single locus VNTR (variable number of tandem repeats) probes MS1, MS31, MS43a and YNH24 are reported. From two blood samples three fragments were obtained with MS1. The consistency of the characteristic allele frequency distribution for each probe is exemplified by comparing the accumulated frequency curves obtained with MS43a in samples consisting of 50 and 920 bands, respectively. The distribution of the differences in migration distance for the two fragments of a bandpair was investigated. The results suggest that the high frequency of apparent homozygotes observed is due mainly to coalescence of close heterozygotes. The distribution of frequencies of 437 DNA-profiles is reported.

Bias↗

PubMed2001

Effects of changes in frequency and inspiratory time on arterial oxygenation and CO2 elimination during high-frequency jet ventilation in a child with laryngotracheal papillomata.

An 11-yr-old female without any pulmonary disorders underwent laser resections of laryngotracheal tumors using high-frequency jet ventilation (HFJV) 6 times over a period of 17 months at our institute. In this series of surgeries, we studied the effects on PaO2 and PaCO2 during HFJV of changes of either frequency or inspiratory time. Increasing the frequency from 100 to 400/min decreased the PaO2 and increased the PaCO2. Decreasing the inspiratory time from 30% to 20% increased the PaCO2, although it did not affect the PaO2. All the procedures were uneventfully carried out without critically impairing gas exchange during HFJV. In this patient with normal lung function, CO2 elimination during HFJV appeared to be facilitated by either decreasing the frequency or increasing the inspiratory time. Arterial oxygen tension during HFJV was higher at lower frequencies.

Carbon Dioxide↗

PubMed1995

High frequency of sex and equal frequencies of mating types in natural populations of the ciliate Tetrahymena thermophila.

In ciliate protists, sex involves the temporary joining of two cells of compatible mating type, followed by meiosis and exchange of gametic nuclei between conjugants. Reproduction is by asexual binary fission following conjugation. For the many ciliates with fixed multiple mating types, frequency-dependent sex-ratio theory predicts equal frequencies of mating types, if sex is common in nature. Here, we report that in natural populations of Tetrahymena thermophila sexually immature cells, indicative of recent conjugation, are found from spring through fall. In addition, the seven mating types occur in approximately equal frequencies, and these frequencies appear to be maintained by interaction between complex, multiple mat alleles and environmental conditions during conjugation. Such genotype-environment interaction determining mating type frequency is rare among ciliates.

Animals↗

PubMed1994

Allele frequencies of the preproenkephalin A (PENK) gene CA repeat in Asians, African-Americans, and Caucasians: lack of evidence for different allele frequencies in alcoholics.

Evidence from animal models and from recent reports on the efficacy of the opioid antagonist naltrexone in the treatment of alcoholism suggests that the endogenous opioid systems may play a role in alcohol seeking behavior. The gene encoding preproenkephalin A (PENK) is flanked at its 3' end by a polymorphic (CA)n repeat. We determined the allele frequencies for this locus in samples of Chinese and Atayal living in Taiwan, Caucasians living in the United States and Byelorussia, and African-Americans living in the United States. We compared the allele frequencies of nonalcoholics in each population with those of alcoholics with or without alcohol-induced organ pathology. There was no difference in allele frequencies within any racial group when alcoholics with or without organ pathology were compared; there was also no difference in allele frequency between nonalcoholics and alcoholics within the two Asian populations, Caucasians, or African-Americans. There were highly significant differences in the frequency of the various length polymorphisms between the Asian, Caucasian, and African-American samples.

Alcoholism↗

PubMed2003

Comparison of ABR stimuli for the early detection of ototoxicity: conventional clicks compared with high frequency clicks and single frequency tonebursts.

Effective objective testing methodology is needed for early detection of the effects of ototoxicity on hearing in patients. The requirements for such testing include responses that are: 1) reliable across test sessions; 2) sensitive to ototoxic change ( > 8 kHz), and 3) recordable in a time-efficient manner. Auditory brainstem responses (ABR) appear well suited to this task however, conventional clicks stimulate primarily mid-frequencies (1-4 kHz) and high frequency tonebursts require too much time. We hypothesized that delivery of a band of high frequencies (a high frequency "click"), would elicit reliable and useful ABRs. In the current study, flat and sloped HF (high frequency) clicks with a bandwidth of 8-14 kHz were used. The purpose was to compare brainstem responses elicited by tonebursts, two HF clicks and conventional clicks. The results show that the reliability of responses to the HF clicks were comparable to the tonebursts and further, both HF clicks produced responses slightly larger than tonebursts.

Acoustic Stimulation↗