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PubMed1985

Speech reception thresholds using conventional vs high-frequency spondees in normals and in subjects with marked high-frequency sensorineural loss.

Spondee threshold (ST) estimates were obtained on 20 normal-hearing adults and 15 adults with high-frequency sensorineural hearing losses sloping off above 500 c/s at about 15-20 db/oct. Stimuli consisted of tapes of a woman's voice speaking permuted lists of 9 conventional (broadband) spondees and of 10 high-frequency-emphasis spondees developed especially for this research using a discrete-frequency analysis. For normals, the correspondence was good between the 3-frequency (.5, 1, 2 kc/s) PTA vs either list. However, for the sensorineural Ss, the mean ST for the conventional spondees was better matched to the 2-frequency PTA (av. of 2 best of .5, 1, 2 kc/s), while the high-frequency-emphasis list STs were better matched to the 3-frequency PTA. It was suggested that high-frequency-emphasis STs be used with such sloping losses and that ST-PTA reliability checks for such Ss be comparisons using a +/- 5-db criterion comparing high-frequency-emphasis STs with 3-frequency PTA. If conventional STs are collected, they should with such Ss be compared to the individual's 2-frequency PTA.

Adult↗

PubMed2006

Frequency flows and the time-frequency dynamics of multivariate phase synchronization in brain signals.

The quantification of phase synchrony between brain signals is of crucial importance for the study of large-scale interactions in the brain. Current methods are based on the estimation of the stability of the phase difference between pairs of signals over a time window, within successive frequency bands. This paper introduces a new approach to study the dynamics of brain synchronies, Frequency Flows Analysis (FFA). It allows direct tracking and characterization of the nonstationary time-frequency dynamics of phase synchrony among groups of signals. It is based on the use of the one-to-one relationship between frequency locking and phase synchrony, which applies when the concept of phase synchrony is not taken in an extended 'statistical' sense of a bias in the distribution of phase differences, but in the sense of a continuous phase difference conservation during a short period of time. In such a case, phase synchrony implies identical instantaneous frequencies among synchronized signals, with possible time varying frequencies of synchronization. In this framework, synchronous groups of signals or neural assemblies can be identified as belonging to common frequency flows, and the problem of studying synchronization becomes the problem of tracking frequency flows. We use the ridges of the analytic wavelet transforms of the signals of interest in order to estimate maps of instantaneous frequencies and reveal sustained periods of common instantaneous frequency among groups of signal. FFA is shown to track complex dynamics of synchrony in coupled oscillator models, reveal the time-frequency and spatial dynamics of synchrony convergence and divergence in epileptic seizures, and in MEG data the large-scale ongoing dynamics of synchrony correlated with conscious perception during binocular rivalry.

Adult↗

PubMed2001

Influence of rate of change of frequency on the overall pitch of frequency-modulated tones.

The mechanism(s) determining pitch may assign less weight to portions of a sound where the frequency is changing rapidly. The present experiments explored the possible effect of this on the overall pitch of frequency-modulated sounds. Pitch matches were obtained between an adjustable unmodulated sinusoid and a sinusoidal carrier that was frequency modulated using a highly asymmetric function with the form of a repeating U or inverted U shaped function. The amplitude was constant during the 400-ms presentation time of each stimulus, except for 10-ms raised-cosine onset and offset ramps. In experiment 1, the carrier level was 50 dB SPL and the geometric mean of the instantaneous frequency of the modulated carrier, fc, was either 0.5, 1, 2, or 8 kHz. The modulation rate (fm) was 5, 10, or 20 Hz. The overall depth (maximum to minimum) of the FM was 8% of fc. For all carrier frequencies, the matched frequency was shifted away from the mean carrier frequency, downwards for the U shaped function stimuli and upwards for the repeated inverted U shaped function stimuli. The shift was typically slightly greater than 1% of fc, and did not vary markedly with fc. The effect of fm was small, but there was a trend for the shifts to decrease with increasing fm for fc = 0.5 kHz and to increase with increasing fm for fc = 2 kHz. In experiment 2, the carrier level was reduced to 20 dB SL and matches were obtained only for fc = 2 kHz. Shifts in matched frequency of about 1% were still observed, but the trend for the shifts to increase with increasing fm no longer occurred. In experiment 3, matches were obtained for a 4-kHz carrier at 50 dB SPL. Shifts of about 1% again occurred, which did not vary markedly with fm. The shifts in matched frequency observed in all three experiments are not predicted by models based on the amplitude- or intensity-weighted average of instantaneous frequency (EWAIF or IWAIF). The shifts (and the pitch shifts observed earlier for two-tone complexes and for stimuli with simultaneous AM and FM) are consistent with a model based on the assumption that the overall pitch of a frequency-modulated sound is determined from a weighted average of period estimates, with the weight attached to a given estimate being inversely related to the short-term rate of change of period and directly related to a compressive function of the amplitude.

Adolescent↗

PubMed1982

Frequency discrimination at 1200 Hz in the presence of high-frequency masking noise.

To evaluate the possible contribution of high-frequency hearing to frequency discrimination at lower frequencies, pure-tone frequency discrimination tasks at 1200 Hz, with and without high-frequency masking noise, were performed by two highly practiced normal-hearing listeners. Signal levels ranged from 10 to 80 dB SPL. Spectra of the three high-frequency masking noises ranged from 1.8 to 2.1 kHz, from 2.8 to 3.1 kHz, and from 4 to 8 kHz. The frequency difference limen (DLF) intensity functions, describing DLFs as a function of signal level which were obtained in the presence of high-frequency masking noise, were essentially the same as the DLF intensity functions obtained without masking noise. These results indicate that high-frequency hearing is not necessary for acute frequency discriminations at low and at middle frequencies.

Adult↗

PubMed1987

Comodulation masking release (CMR): effects of signal frequency, flanking-band frequency, masker bandwidth, flanking-band level, and monotic versus dichotic presentation of the flanking band.

In experiment I, thresholds for 400-ms sinusoidal signals were measured in the presence of a continuous 25-Hz-wide noise centered at signal frequencies (fs) ranging from 250 to 8000 Hz in 1-oct steps. The masker was presented either alone or together with a second continuous 25-Hz-wide band of noise (the flanking band) whose envelope was either correlated with that of the on-frequency band or was uncorrelated; its center frequency ranged from 0.5 fs to 1.5 fs. The flanking band was presented either in the same ear (monotic condition) as the signal plus masker or in the opposite ear (dichotic condition). The on-frequency band and the flanking band each had an overall level of 67 dB SPL. The comodulation masking release, CMR (U-C), is defined as the difference between the thresholds for the uncorrelated and correlated conditions. The CMR (U-C) showed two components: a broadly tuned component, occurring at all signal frequencies and all flanking-band frequencies, and occurring for both monotic and dichotic conditions; and a component restricted to the monotic condition and to flanking-band frequencies close to fs. This sharply tuned component was small for low signal frequencies, increased markedly at 2000 and 4000 Hz, and decreased at 8000 Hz. Experiment II showed that the sharply tuned component of the CMR (U-C) was slightly reduced in magnitude when the level of the flanking band was 10 dB above that of the on-frequency band and was markedly reduced when the level was 10 dB below, whereas the broadly tuned component and the dichotic CMR (U-C) were only slightly affected. Experiment III showed that the sharply tuned component of the CMR (U-C) was markedly reduced when the bandwidths of the on-frequency and flanking bands were increased to 100 Hz, while the broadly tuned component and the dichotic CMR (U-C) decreased only slightly. The argument here is that the sharply tuned component of the monotic CMR (U-C) results from beating between the "carrier" frequencies of the two masker bands. This introduces periodic zeros in the masker envelope, which facilitate signal detection. The broadly tuned component, which is probably a "true" CMR, was only about 3 dB.

Attention↗

PubMed1999

Positive force- and [Ca2+]i-frequency relationships in rat ventricular trabeculae at physiological frequencies.

The isometric force-frequency relationship of isolated rat ventricular trabeculae (diameter <250 micrometer) was examined at 24, 30, and 37 degreesC at stimulation frequencies (0.1-12 Hz) encompassing the physiological range. Some muscles were microinjected with fura PE3 to monitor the diastolic and systolic intracellular concentration of Ca2+ ([Ca2+]i). At a near-physiological external Ca2+ concentration ([Ca2+]o) of 1 mM, a positive force-frequency relationship was demonstrated at all temperatures. The force-frequency relationship became negative at high frequencies (e. g., >6 Hz at 30 degreesC) at 1 mM [Ca2+]o or at low frequencies at 8 mM [Ca2+]o. The twitch and Ca2+ transient became shorter as stimulation frequency increased; these changes were related to changes in systolic, rather than diastolic, [Ca2+]i and were not blocked by inhibitors of Ca2+/calmodulin-dependent protein kinase II. The positive force-frequency relationship of rat trabeculae was caused by a frequency-dependent loading of the sarcoplasmic reticulum (SR) with Ca2+. We suggest that at high frequencies, or under conditions of Ca2+ overload, this loading saturates. Processes that tend to decrease SR Ca2+ release will then predominate, resulting in a negative force-frequency relationship.

Animals↗

PubMed1991

Hopping frequency in humans: a test of how springs set stride frequency in bouncing gaits.

The storage and recovery of elastic energy in muscle-tendon springs is important in running, hopping, trotting, and galloping. We hypothesized that animals select the stride frequency at which they behave most like simple spring-mass systems. If higher or lower frequencies are used, they will not behave like simple spring-mass systems, and the storage and recovery of elastic energy will be reduced. We tested the hypothesis by having humans hop forward on a treadmill over a range of speeds and hop in place over a range of frequencies. The body was modeled as a simple spring-mass system, and the properties of the spring were measured by use of a force platform. Our subjects used nearly the same frequency (the "preferred frequency," 2.2 hops/s) when they hopped forward on a treadmill and when they hopped in place. At this frequency, the body behaved like a simple spring-mass system. Contrary to our predictions, it also behaved like a simple spring-mass system when the subjects hopped at higher frequencies, up to the maximum they could achieve. However, at the higher frequencies, the time available to apply force to the ground (the ground contact time) was shorter, perhaps resulting in a higher cost of generating muscular force. At frequencies below the preferred frequency, as predicted by the hypothesis, the body did not behave in a springlike manner, and it appeared likely that the storage and recovery of elastic energy was reduced. The combination of springlike behavior and a long ground contact time at the preferred frequency should minimize the cost of generating muscular force.

Adult↗

PubMed2003

The effect of training on frequency discrimination: generalization to untrained frequencies and to the untrained ear.

While there is growing evidence that frequency discrimination improves with practice, there are, however, limited and inclusive reports regarding the generalization of learning to untrained conditions. The goals of the present study were therefore (1) to measure the effect of multi-session training on difference limen frequency (DLF) thresholds and evaluate the relative contribution of procedural and stimulus learning by comparison to a control (untrained) group; (2) to evaluate the extent of generalization of the trained frequency to two untrained frequencies known to be temporally coded; and (3) to estimate the generalization of the trained frequency to the untrained ear, for both trained and untrained frequencies. Two groups of subjects were included: a trained group (n = 5) and a control group (n = 5). For the trained group, DLF thresholds for 1 kHz (trained frequency) and 1.1 and 2.0 kHz (untrained frequencies) were obtained using a two-interval, two-alternative forced choice paradigm before and after an eight-session training. The control group was tested using the same stimuli only twice, with a 3-week interval between testing. Results showed that (1) multi-session training improves frequency discrimination in normal hearing young adults; (2) adding a control group to the study allowed estimation of the effect of limited exposure to the stimuli and task in naïve listeners and evaluation of the magnitude of procedural learning; (3) learning was generalized across frequencies that are coded by similar mechanisms; (4) generalization of learning occurred in the untrained ear for trained and untrained frequencies. These results have important clinical and theoretical implications regarding the processes underlying perceptual learning and the effectiveness of auditory habilitation strategies.

Acoustic Stimulation↗

PubMed2005

[Studies on the spectrum and frequency repetition of double-mode He-Ne laser with frequency stabilization].

Theoretical analysis of spectrum and frequency repetition of the double-model frequency stabilization He-Ne laser has been done, and the beat frequency experiment using 632 nm I2 frequency stabilization He-Ne laser has been carried out. The authors used the intercavity laser, and the double mode frequency stabilization to get the laser stabilized output through adjusting the two neighbor vertically polarized modes to the equal power reference point. Through the experiment, the authors analyzed the factors which affect the laser frequency repetition and stabilization, and measured the stabilized laser power and the frequency stabilization. The beat frequency experiment has shown that the frequency repetition can reach (1-2) x 10(-8) by frequency difference, and the laser stabilization can reach 10(-10) by Allan variances. The experiments show that the stabilized laser can work well and can be used as frequency reference point.

Algorithms↗

PubMed2004

Frequency Finder: a multi-source web application for collection of public allele frequencies of SNP markers.

Publicly available single nucleotide polymorphism (SNP) allele frequencies are an important resource for the selection of genetic markers that may be most useful for gene mapping and association studies. Data mining these allele frequencies through disparate public databases and Websites is time consuming and can result in inconsistent findings. We have developed a web-based software tool, Frequency Finder, to acquire SNP allele frequencies from multiple public data sources and return a summarized result to the user. Our software optimizes and automates the search of candidate markers, decreasing the amount of time it would take to extract pertinent data manually. We have included several methods to output the data, including on-screen and as a compressed text file. We show that Frequency Finder accurately retrieves available frequency data from the available sources. Using this tool, we detect significant differences between Asian, African and Caucasian populations in the allele frequency spectra of 246 097 SNPs. While limited to public databases that provide web-based access to allele frequencies, Frequency Finder provides a single, user-friendly interface for retrieving allele frequencies for large batches of SNPs from multiple data sources.

Algorithms↗

PubMed1995

Frequencies of the blood groups ABO, Rhesus, D category VI, Kell, and of clinically relevant high-frequency antigens in south-western Germany.

BACKGROUND: Current estimates of blood group frequencies in Germany were often derived from studies involving less than 12,000 individuals. The frequency of the D category VI was unknown. METHODS: ABO. Kell, and Rhesus blood group data of more than 600,000 donors were reviewed. Allele frequencies were derived by the maximum-likelihood method. The frequency of D category VI was determined in more than 70,000 Rhesus typings. RESULTS: ABO allele frequencies were: O: 0.640, A: 0.279. B: 0.081. Rhesus haplotype frequencies were: cde: 0.394, CDe: 0.431, cDE: 0.136, cDe: 0.021, and Cde: 0.011. D category VI represented 7%, of all weak D (formerly D(u)). The 95% confidence interval for the D category VI frequency was 1:3,600-1:11,200. Kell allele frequencies were: K: 0.040, and k: 0.960, 95% confidence intervals for rare phenotypes were: Oh: 1:88,000-1:1,760,000, p: 1:200,000-1:5,200,000. Rh(null): 1:180,000-1:10,300,000, and D-deletion: 1: 180,000-0. CONCLUSIONS: We presented refined estimates of ABO, Rhesus D and Kell blood group frequencies and established reliable frequency estimates for Rhesus haplotype and some rare blood groups. The prevalence of D category VI was about 0.02%, which necessitates specific detection for Rh-D-negative transfusion therapy. A protocol is presented for Rh D typing in transfusion recipients. which obviates the need for an antiglobulin test.

ABO Blood-Group System↗

PubMed1996

Mutation frequencies but not mutant frequencies in Big Blue mice fit a Poisson distribution.

Transgenic mutation assays generally use mutant frequencies to estimate mutation frequencies but the degree to which clonal expansion inflates mutant frequencies is largely unknown. Mutant frequency is defined as the fraction of cells carrying mutations in the gene of interest and, according to the standard Big Blue protocol, is determined by dividing the number of mutant plaques by the total number of plaques screened. Mutation frequency is determined as the fraction of cells carrying definitely independent mutations and therefore requires correction for clonal expansion. Mutant and mutation frequencies were determined for brain, thymus and male germ cells of four mice from two age groups (3-versus 10-month old). The mutant frequency in thymus differed significantly between 3- and 10-month old mice (P < 0.05). By sequencing all mutants, the mutation frequency (i.e., corrected for jackpot mutations) in thymus was determined and was not significantly different between 3- and 10-month old mice. Mutant frequency does not fit a Poisson distribution, but mutation frequency corrected for jackpot mutations is substantially less variable and does fit a Poisson distribution.

Age Factors↗

PubMed2001

Frequency discrimination threshold at search call frequencies in the echolocating bat, Eptesicus fuscus.

While searching for prey in open spaces, Epteisicus fuscus emits long-duration, downward frequency-modulated calls which cover a frequency band of about 28-22 kHz. In the ascending auditory pathways of E. fuscus, neurons tuned to these search call frequencies are characterised by a remarkably high frequency selectivity and very sensitive absolute thresholds. We investigated whether this narrow tuning is reflected in an exceptional psychoacoustic frequency discrimination ability. The average frequency difference limen of E. fuscus at search call frequencies determined in a two-alternative, forced-choice experiment amounted to about 420 Hz, corresponding to a Weber ratio of 0.017. This value is similar to those found in non-echolocating mammals, and an order of magnitude larger than the frequency difference limens of bats emitting constant-frequency call components. We discuss these differences in frequency difference limen, and relate them to different echolocation strategies.

Acoustics↗

PubMed2006

Acoustic model investigation of a multiple carrier frequency algorithm for encoding fine frequency structure: implications for cochlear implants.

Current cochlear implants provide frequency resolution through the number of channels. Improving resolution by increasing channels is limited by factors such as the physiological feasibility of increasing the number of electrodes, the inability to increase the number of channels for those already implanted, and the increased possibility of channel interactions reducing channel efficacy. Recent studies have suggested an alternative method: providing a continuum of pitch percepts for each channel based on the frequency content of that channel. This study seeks to determine the frequency resolution necessary for the highest performance gain, which may give some indication of the feasibility for implementation in implants. A discrete set of carrier frequencies, instead of a continuum, are evaluated using an acoustic model to measure speech recognition. Performance increased as the number of available frequencies increased, and substantive improvement was seen with as few as two frequencies per channel. The effect of variable frequency discrimination was also assessed, and the results suggest that frequency modulation can still provide benefits with poor frequency discrimination on some channels. These results suggest that if two or more discriminable frequencies per channel can be generated for cochlear implant subjects then an improvement in speech recognition may be possible.

Acoustics↗

PubMed2000

Differential effects of high-frequency versus low-frequency exercise training in rehabilitation of patients with coronary artery disease.

OBJECTIVES: We sought to study the influence of frequency of exercise training during cardiac rehabilitation on functional capacity (i.e., peak oxygen consumption [VO2] and ventilatory anaerobic threshold [VAT]) and quality of life (QoL). BACKGROUND: Although the value of cardiac rehabilitation is now well established, the influence of the different program characteristics on outcome has received little attention, and the effect of frequency of exercise training is unclear. Functional capacity is regularly evaluated by peak VO2 but parameters of submaximal exercise capacity such as VAT should also be considered because submaximal exercise capacity is especially important in daily living. METHODS: Patients with coronary artery disease (n = 130, 114 men; mean age 52 +/- 9 years) were randomized to either a high- or low-frequency program of six weeks (10 or 2 exercise sessions per week of 2 h, respectively). Functional capacity and QoL were assessed before and after cardiac rehabilitation. Global costs were also compared. RESULTS: Compared with baseline, mean exercise capacity increased in both programs: for high- and low-frequency, respectively: peak VO2 = 15% and 12%, Wmax = 18% and 12%, VAT = 35% and 12% (all p < 0.001). However, when the programs were compared, only VAT increased significantly more during the high-frequency program (p = 0.002). During the high-frequency program, QoL increased slightly more, and more individuals improved in subjective physical functioning (p = 0.014). We observed superiority of the high-frequency program, especially in younger patients. Mean costs were estimated at 4,455 and 2,273 Euro, respectively, for the high- and low-frequency programs. CONCLUSIONS: High-frequency exercise training is more effective in terms of VAT and QoL, but peak VO2 improves equally in both programs. Younger patients seem to benefit more from the high-frequency training.

Adult↗

PubMed1981

Tidal volume and frequency dependence of carbon dioxide elimination by high-frequency ventilation.

Six patients with chronic respiratory failure received mechanical ventilation with tidal volumes less than or equal to the dead-space volume, at frequencies of 30 to 900 breaths per minute. The rate of elimination of carbon dioxide from the ventilator system during a brief trial of high-frequency ventilation accurately predicted the long-term effectiveness of a given combination of frequency and tidal volume. Below frequencies of about 200 breaths per minute, the volume of carbon dioxide eliminated from these patients was most strongly related to the product of frequency and tidal volume; at higher frequencies, carbon dioxide elimination was determined by the tidal volume and was independent of frequency. These results suggest that although the effectiveness of high-frequency ventilation is primarily a function of the product of tidal volume and frequency, above a critical frequency the mechanical characteristics of the lung reduce gas transport by limiting the volume transmitted to the periphery of the lung.

Adolescent↗

PubMed1997

Frequency discrimination vs frequency estimation: adult age differences and the effect of divided attention.

In this experiment we explored age differences in frequency judgment. Young and older adults studied words occurring from one to six times under divided or focused attention and then completed either a frequency discrimination or a frequency estimation test for these items. Divided attention led to poorer performance on both frequency judgment tests, suggesting that distraction during the encoding of target events results in less optimal encoding of the information that is necessary for any type of frequency judgment. Contrary to the notion that older adults encode this information more superficially than young adults, older adults were as sensitive as young adults to relative differences in the frequency of target words, and distraction did not magnify age differences for either type of frequency judgment task. On the other hand, older adults were less accurate in assigning an absolute numerical value to the frequency of the target words. Altogether, the results are consistent with the idea that the encoding and/or retrieval processes required for accurate numerical estimation of frequency suffer a larger age-related decline than do those required for accurate discrimination of relative frequency.

Adult↗

PubMed1992

Time-frequency transforms: a new approach to first heart sound frequency dynamics.

This study employed a new analytical tool, the Binomial joint time-frequency transform, to test the hypothesis that first heart sound frequency rises during the isovolumic contraction period. Cardiac vibrations were recorded from eight open chest dogs using an ultralight accelerometer cemented directly to the epicardium of the anterior left ventricle. The frequency response of the recording system was flat +/- 3 dB from 0.1 to 400 Hz. Three characteristic time-frequency spectral patterns were evident in the animals investigated: 1) A frequency component that rose from approximately 40-140 Hz in a 30-50 ms interval immediately following the ECG R-wave. 2) A slowly varying or static frequency of 60-100 Hz beginning midway through the isovolumic contraction period. 3) Broad-band peaks occurring at the time of the Ia and Ib high frequency components. The presence of rapid frequency dynamics limits the usefulness of stationary analysis techniques for the first heart sound. The Binomial transform provided much better resolution than the spectrograph or spectrogram, the two most common non-stationary signal analysis techniques. By revealing the onset and dynamics of first heart sound frequencies, time-frequency transforms may allow mechanical assessment of individual cardiac structures.

Animals↗