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PubMed1998

Use of amplitude-modulated breathing for assessment of cardiorespiratory frequency response within subrespiratory frequencies.

We present a new technique which uses amplitude-modulated breathing patterns to obtain estimates of frequency response between respiration and heart rate within subrespiratory frequencies. Frequency response between respiration and heart rate has been previously estimated using broadband respiration and metronomic breathing. However, the estimates obtained using these techniques show low coherence between respiration and heart rate within the subrespiratory frequencies (< 0.12-0.15 Hz). The advantages of amplitude-modulated breathing are: enhancement in the degree of perturbation within subrespiratory frequencies as indicated by relatively higher coherencies between respiration and heart rate (approximately equal to 0.7), and the subjects do not have to breathe at very low breathing frequencies or resort to breath holds. Use of a squared sine wave carrier modulated by sinusoidal functions enabled us to obtain energy distributions at subrespiratory frequencies without using demodulation. Results obtained at eight subrespiratory frequencies from ten subjects show that the new technique is easy to implement and produces relatively higher coherence between respiration and heart rate. The advantage of the new technique in terms of enhancing the level of perturbations within subrespiratory frequencies is particularly important, because it is in this frequency range that the interpretation of variability in heart rate in terms of autonomic origins is incompletely understood and is confounded by respiratory interactions.

Adult↗

PubMed2005

Predicting fundamental frequency from mel-frequency cepstral coefficients to enable speech reconstruction.

This work proposes a method to reconstruct an acoustic speech signal solely from a stream of mel-frequency cepstral coefficients (MFCCs) as may be encountered in a distributed speech recognition (DSR) system. Previous methods for speech reconstruction have required, in addition to the MFCC vectors, fundamental frequency and voicing components. In this work the voicing classification and fundamental frequency are predicted from the MFCC vectors themselves using two maximum a posteriori (MAP) methods. The first method enables fundamental frequency prediction by modeling the joint density of MFCCs and fundamental frequency using a single Gaussian mixture model (GMM). The second scheme uses a set of hidden Markov models (HMMs) to link together a set of state-dependent GMMs, which enables a more localized modeling of the joint density of MFCCs and fundamental frequency. Experimental results on speaker-independent male and female speech show that accurate voicing classification and fundamental frequency prediction is attained when compared to hand-corrected reference fundamental frequency measurements. The use of the predicted fundamental frequency and voicing for speech reconstruction is shown to give very similar speech quality to that obtained using the reference fundamental frequency and voicing.

Dichotic Listening Tests↗

PubMed1987

Frequency discrimination of complex signals, frequency selectivity, and speech perception in hearing-impaired subjects.

Frequency discrimination of spectral envelopes of complex stimuli, frequency selectivity measured with psychophysical tuning curves, and speech perception were determined in hearing-impaired subjects each having a relatively flat, sensory-neural loss. Both the frequency discrimination and speech perception measures were obtained in quiet and noise. Most of these subjects showed abnormal susceptibility to ambient noise with regard to speech perception. Frequency discrimination in quiet and frequency selectivity did not correlate significantly. At low signal-to-noise ratios, frequency discrimination correlated significantly with frequency selectivity. Speech perception in noise correlated significantly with frequency selectivity and with frequency discrimination at low signal-to-noise ratios. The frequency discrimination data are discussed in terms of an excitation-pattern model. However, they neither support nor refute the model.

Auditory Perception↗

PubMed1994

The critical modulation frequency and its relationship to auditory filtering at low frequencies.

If the thresholds for detecting sinusoidal amplitude or frequency modulation of a sinusoidal carrier with frequency fc are expressed in terms of the respective modulation indices, m and beta, the ratio beta/m decreases as the modulation frequency increases, and approaches an asymptotic value of unity. The modulation frequency at which the ratio first becomes unity is called the critical modulation frequency (CMF). It has been suggested that the CMF is reached when the spectral sidebands in the stimulus first become detectable and that the CMF corresponds to half the value of the critical bandwidth (CB) at fc. In this paper it is demonstrated that the CMF is confounded as a measure of frequency selectivity at low frequencies, since, for modulation frequencies around the CMF, the sideband that is most detectable changes with fc. For values of fc above 250 Hz, the lower sideband is most detectable. For values of fc below 200 Hz, the upper sideband is most detectable. These findings can account for the fact that the CMF flattens off at low carrier frequencies, reaching an asymptotic value of about 40 Hz, whereas the auditory filter bandwidth continues to decrease down to very low center frequencies.

Acoustic Stimulation↗

PubMed1993

Optimal frequency of radiofrequency catheter ablation in vitro and in vivo for treating ventricular tachycardias--a study using various frequencies.

The purpose of this study was to determine the optimal frequency for radiofrequency catheter ablation of ventricular tachycardias. A radiofrequency current was delivered from a 6F bipolar electrode catheter with a tip electrode width of 4 mm. Ablation was performed for a pulse duration of 10 sec at 20 watts (50 V and 0.4 A) at seven different frequencies between 10 and 500 kHz. We used 35 canine isolated left ventricular endocardial sites in vitro and 14 anesthetized dogs in vivo. The lesions which were ablated at frequencies of 200 and 300 kHz were significantly larger than those at other frequencies, with a mean surface areas of 78.5 and 76.3 mm2, and mean depths of 4.0 and 4.1 mm, respectively (p < 0.05). The appearance of ventricular arrhythmias during ablation increased as the frequency decreased. One dog, to which a frequency of 100 kHz was applied, developed spontaneous ventricular fibrillation and died. All of the dogs which received a current with a frequency under 50 kHz exhibited muscle cramping during ablation. Ventricular stimuli applied after ablation did not induce ventricular tachycardia. These results suggest that the optimal frequency for ablating a large lesion is between 200 and 300 kHz. To avoid inducing malignant ventricular arrhythmia during ablation, the frequency must exceed 200 kHz. Furthermore, a frequency below 100 kHz should not be used in radiofrequency catheter ablation because of the risk of arrhythmias and muscle cramping.

Animals↗

PubMed2005

Spike frequency is dependent on epilepsy duration and seizure frequency in temporal lobe epilepsy.

OBJECTIVES: We wanted to investigate factors that are associated with frequency of interictal epileptiform discharges by investigating 303 patients with temporal lobe epilepsy (TLE). METHODS: We included all patients who consecutively underwent the adult presurgical evaluation program at our center and who had intractable, medial TLE with complex partial seizures due to unilateral medial temporal lobe lesions. The interictal EEG samples were automatically recorded and stored on computer. The location and frequency of interictal epileptiform discharges were assessed by visual analysis of interictal EEG samples of 2-minute duration every hour. RESULTS: There were 303 patients (aged 16-63) who met the inclusion criteria. The median interictal epileptiform discharge frequency was 15 IED/h, the median seizure frequency was 4 seizures/month. According to univariate analyses, we found that age at monitoring, epilepsy duration, and higher seizure frequency were associated with higher interictal epileptiform discharge frequency. In the logistic regression analysis, we found that higher seizure frequency (p < 0.001) and longer epilepsy duration (p = 0.007) were independently associated with higher spike frequency, while the age at monitoring was not. CONCLUSIONS: Seizure frequency and epilepsy duration (years of patient's life with seizure activity) were independently associated with IED frequency, suggesting that IED are modulated by seizures.

Adolescent↗

PubMed2006

The effects of high-frequency amplification on the objective and subjective performance of hearing instrument users with varying degrees of high-frequency hearing loss.

PURPOSE: The purpose of the present study was to determine if amplifying beyond 2 kHz affected the objective and subjective performance of hearing instrument users with varying degrees of mild-to-severe high-frequency sensorineural hearing loss. METHOD: Twenty participants were fitted binaurally with digital completely-in-the-canal devices with 4-channel wide dynamic range compression (Starkey Axent). Each participant used the hearing instruments for two 6-week trial periods. Each hearing instrument was programmed to maximize high-frequency audibility during 1 trial period and minimize high-frequency audibility during the other trial period. Objective evaluations were conducted in quiet using the Connected Speech Test (CST) and in noise using the CST and the Hearing in Noise Test. Subjective performance was evaluated by administering the Abbreviated Profile of Hearing Aid Benefit and a questionnaire. RESULTS: Results indicated that high-frequency amplification significantly improved objective performance in noise and subjective preference in quiet for listeners with varying degrees of mild-to-severe high-frequency hearing loss. Results also suggested that high-frequency amplification may affect subjective preference in noise and overall for listeners with varying degrees of mild-to-severe high-frequency hearing loss when feedback is eliminated. CONCLUSION: Based on these significant benefits, dispensers should be aware that high-frequency amplification should, at least initially, be provided to the affected high-frequency regions when mild-to-severe hearing loss is present.

Acoustic Stimulation↗

PubMed1992

Frequency of chronic lung disease in infants with severe respiratory failure treated with high-frequency ventilation and/or extracorporeal membrane oxygenation.

OBJECTIVE: To assess the frequency of chronic lung disease and factors associated with its development in term infants with severe respiratory failure who receive high-frequency oscillatory ventilation, or high-frequency oscillatory ventilation, and extracorporeal membrane oxygenation (ECMO). DESIGN: Retrospective review of pulmonary outcome of all ECMO candidates admitted to Wilford Hall USAF Medical Center between July 1985 and September 1989. SETTING: A tertiary, level III, neonatal ICU accepting regional referrals for high-frequency ventilation and ECMO. PATIENTS: Ninety-four patients who were candidates for ECMO were studied. High-frequency oscillatory ventilation alone was used in 48 infants. Forty-six infants were treated with high-frequency oscillatory ventilation and ECMO. MAIN RESULTS: Twenty (24%) of 84 survivors developed chronic lung disease. There were no differences in gestational age, birth weight, or gender between those infants who developed chronic lung disease and those infants who did not. Arterial blood gas and ventilatory settings at initiation of high-frequency oscillatory ventilation were similar between those infants who did and those who did not develop chronic disease. Patients who developed chronic lung disease more often had lung hypoplasia (40% vs. 5%) and more often required ECMO (75% vs. 39%) than those patients who did not. In patients without lung hypoplasia, those patients who developed chronic lung disease were older at initiation of high-frequency oscillatory ventilation rescue than those patients who did not develop chronic lung disease (median 91 vs. 46 hrs). CONCLUSIONS: The frequency of chronic lung disease in ECMO candidates is clinically important. Factors associated with chronic lung disease in ECMO candidates are: the presence of lung hypoplasia, delayed referral, and the need for ECMO to support gas exchange.

Birth Weight↗

PubMed1988

Frequency response evaluation of radial artery catheter-manometer systems: sinusoidal frequency analysis versus flush method.

It is well recognized that catheter-manometer systems significantly distort direct radial artery pressure measurements. Sinusoidal frequency analysis and the flush method of assessing the degree of distortion caused by the monitoring system were compared to determine whether these two methods agree in the estimation of natural frequency and damping coefficient. The frequency response of 30 radial artery catheter-manometer systems used for intensive-care unit patients was measured by the flush method and sinusoidal frequency analysis. The monitoring system consisted of a 20-gauge cannula, 150-cm pressure tubing, two plastic stopcocks, a continuous infusion device with fast flush valve, an American Edwards dome, a Hewlett-Packard quartz transducer, and a Hewlett-Packard blood pressure amplifier. Sinusoidal frequency analysis demonstrated second-order underdamped response for all 30 catheter-manometer systems. No secondary resonance peaks were observed up to a frequency of 200 Hz. The measured frequency response demonstrated that the average catheter-manometer system in use in our intensive care unit would cause significant distortion of the radial artery pressure, with the mean natural frequency (fn) of 14.7 +/- 3.7 Hz and the mean damping coefficient (zeta) of 0.24 +/- 0.07. Although the 30 monitoring systems had identical configurations and visible bubbles were carefully removed, a wide range of frequency responses was found (fn = 10.2 to 25.3; zeta = 0.15 to 0.44).(ABSTRACT TRUNCATED AT 250 WORDS)

Arm↗

PubMed1990

The influence of spatial frequency on perceived temporal frequency and perceived speed.

Speed matching experiments were conducted using drifting gratings of different spatial frequencies in order to assess the influence of spatial frequency on perceived speed. It was found that gratings of high spatial frequency appear to drift more slowly than low spatial frequency gratings of the same actual velocity. The perceived temporal frequency of a counterphase grating similarly declines as spatial frequency increases. The previously reported effect of temporal frequency on perceived spatial frequency probably does not contribute to these phenomena. Our results suggest that the motion sensors thought to operate within different spatial frequency ranges have different velocity transfer functions, a fact not incorporated in existing computational models of motion perception.

Contrast Sensitivity↗

PubMed1993

Peripheral temporal frequency channels code frequency and speed inaccurately but allow accurate discrimination.

Perceived temporal frequency is vastly underestimated in the peripheral visual field, as all temporal frequencies above 10 Hz are perceived as flickering at 10 Hz even after scaling for acuity. Varying the contrast and spatial frequency of the peripheral pattern four-fold have negligible effects on the perceived flicker rate. Speed and auditory matching experiments also support this finding. Despite the saturation of perceived temporal frequency, frequency discrimination beyond 10 Hz was as accurate as in the fovea. By using a temporal masking paradigm, we obtained threshold elevation data that could be accounted for by three overlapping, broadly tuned temporal channels peaking at 5.5, 12 and 22 Hz. Based on these temporal frequency channels, we proposed that the visual system uses a line-element scheme for mediating temporal frequency discrimination, but adopts a weighted-average method for determining perceived temporal frequency. In the peripheral visual field, the weight assigned to the highest temporal channel is much larger than those assigned to the lower frequency channels.

Contrast Sensitivity↗

PubMed2005

The relative contributions of speaking fundamental frequency and formant frequencies to gender identification based on isolated vowels.

The purpose of this study was to determine the accuracy with which listeners could identify the gender of a speaker from a synthesized isolated vowel based on the natural production of that speaker when (1) the fundamental frequency was consistent with the speaker's gender, (2) the fundamental frequency was inconsistent with the the speaker's gender, and (3) the speaker was transgendered. Ten male-to-female transgendered persons, 10 men and 10 women, served as subjects. Each speaker produced the vowels /i/, /u/, and //. These vowels were analyzed for fundamental frequency and the first three formant frequencies and bandwidths. Formant frequency and bandwidth information was used to synthesize two vowel tokens for each speaker, one at a fundamental frequency of 120 Hz and one at 240 Hz. Listeners were asked to listen to these tokens and determine whether the original speaker was male or female. Listeners were not aware of the use of transgendered speakers. Results showed that, in all cases, gender identifications were based on fundamental frequency, even when fundamental frequency and formant frequency information was contradictory.

Adult↗

PubMed2004

Spatial frequency selective masking of first-order and second-order motion in the absence of off-frequency 'looking'.

Converging evidence suggests that, at least initially, first-order (luminance defined) and second-order (e.g. contrast defined) motion are processed independently in human vision. However, adaptation studies suggest that second-order motion, like first-order motion, may be encoded by spatial frequency selective mechanisms each operating over a limited range of scales. Nonetheless, the precise properties of these mechanisms are indeterminate since the spatial frequency selectivity of adaptation aftereffects may not necessarily represent the frequency tuning of the underlying units [Vision Research 37 (1997) 2685]. To address this issue we used visual masking to investigate the spatial-frequency tuning of the mechanisms that encode motion. A dual-masking paradigm was employed to derive estimates of the spatial tuning of motion sensors, in the absence of off-frequency 'looking'. Modulation-depth thresholds for identifying the direction of a sinusoidal test pattern were measured over a 4-octave range (0.125-2 c/deg) in both the absence and presence of two counterphasing masks, simultaneously positioned above and below the test frequency. For second-order motion, the resulting masking functions were spatially bandpass in character and remained relatively invariant with changes in test spatial frequency, masking pattern modulation depth and the temporal properties of the noise carrier. As expected, bandpass spatial frequency tuning was also found for first-order motion. This provides compelling evidence that the mechanisms responsible for encoding each variety of motion exhibit spatial frequency selectivity. Thus, although first-order and second-order motion may be encoded independently, they must utilise similar computational principles.

Humans↗

PubMed1994

The frequency and frequency dysuria syndromes of childhood: hypercalciuria as a possible etiology.

OBJECTIVES: The syndromes of frequency and frequency dysuria of childhood are believed to have multifactorial etiologies. Hypercalciuria has been reported to be associated with the frequency dysuria syndrome and a direct cause and effect relationship has been postulated due to a positive response to treatment with hydrochlorothiazide. This study was designed to compare the urinary calciums of children with the frequency syndrome and the frequency dysuria syndrome. METHODS: Calcium screening in 30 consecutive patients with the frequency syndrome and 39 consecutive patients with the frequency dysuria syndrome is reported. RESULTS: There was no statistical difference in the urinary calcium excretion in the two groups. CONCLUSIONS: There was no significant difference in the calcium excretion in children with isolated urinary frequency or frequency dysuria. No definite cause and effect relationship to hypercalciuria could be identified in these two groups.

Adolescent↗

PubMed1994

Lateralization of high frequency, amplitude modulated sounds as a function of carrier frequency.

Twenty subjects made graphic ratings of the perceived laterality of amplitude modulated sounds that were presented through earphones. A 200 Hz modulation frequency was combined with carrier frequencies of 2200 Hz, 3200 Hz, 4200 Hz, and 5200 Hz. The modulator sinusoid was delayed to either ear by temporal intervals ranging from zero to 0.6 ms. A significant interaction of carrier frequency with the linear trend for interaural temporal disparity indicated that the slopes of laterality ratings on temporal disparity decreased with carrier frequency. A significant interaction of carrier frequency with the difference in ratings for the 0.6 ms delays to the two ears indicated that the range in laterality ratings decreased with carrier frequency. The results indicate that the amount of laterality is a decreasing function of carrier frequency for high frequency sounds, which may be a consequence of greater weight being given to zero intensity difference as frequency increases.

Auditory Perception↗

PubMed1999

Effects of monitoring condition and frequency-altered feedback on stuttering frequency.

The purpose of the study was to examine stuttering frequency during speaking conditions that are believed to mitigate stuttering frequency both with normal nonaltered auditory feedback (NAF) and a known fluency-enhancing feedback. Specifically, stuttering frequency was examined as a function of three monitoring conditions under NAF and frequency-altered feedback (FAF): no monitoring (i.e., speaking alone, in the absence of audio and visual recording), audiovisual monitoring (i.e., speaking alone with audiovisual recording), and audiovisual monitoring with observers (i.e., speaking with audiovisual recording in the presence of two observers). Seven adults and one adolescent who stutter served as participants. Stuttering frequency was differentially affected across monitoring conditions under each auditory feedback condition (p = .027). Post hoc analyses revealed no significant difference in stuttering frequency between the two conditions in the absence of the observers (i.e., no monitoring vs. audiovisual monitoring) under NAF (p = .45). There was, however, a significant difference in stuttering frequency for the no-monitoring and audiovisual-monitoring conditions relative to the audiovisual-monitoring-with-observers condition (p = .0002). There was no statistically significant difference in stuttering frequency across monitoring conditions under FAF (p > .05). The findings are consistent with the notion that during NAF stuttering frequency varies as a function of hierarchical socio-environmental conditions in which inanimate monitoring conditions constitute one entity. Such a relationship does not exist during FAF.

Adult↗

PubMed2003

Lower receiving frequencies than transmitting frequencies could yield improved results for contrast imaging: an in vivo study in closed chest canines.

BACKGROUND: Ultrasonic imaging methods of receiving at higher frequencies, which are multiples of the transmitting frequencies (harmonic imaging), are well established as a means of improving myocardial visualization in association with intravenous contrast administration. This exploratory study examined the effect of using receive frequencies that were lower than the transmit frequencies while imaging closed chest dogs with an Ensemble wideband, phase inversion contrast program on a modified Siemens Elegra scanner. METHODS: Intravenous bolus injections of 0.75 mL Definity and 1 mL QW7437 were administered to six anesthetized dogs. Intermittent imaging for contrast visualization was performed using either a broadband array, transmitting at 1.4 MHz and receiving at 2.6-3.2 MHz or a broadband 4-7.5 MHz transducer transmitting at 6.0 MHz and receiving at 4.2-4.5 MHz. Contrast enhancement was measured by videodensitometry, sampling mid-cavity and within the myocardium before and after injection. The changes in videodensity from control to after injection were calculated for each method. RESULTS: There was no significant difference in the change in intracavity videodensity between the two imaging strategies although there was near full intracavity saturation in all cases. However, the change in myocardial density was significantly greater for both contrast agents when using receiving frequencies lower than transmitting frequencies (P = 0.02 and 0.03). The difference in duration of the myocardial blush did not reach statistical significance but it tended to persist for longer with the lower receiving frequencies. CONCLUSION: Delivering sound energy at a slightly higher frequency and receiving at lower than the transmit frequency may be an advantageous method of enhancing myocardial perfusion signals during intravenous contrast echocardiography.

Animals↗

PubMed2002

Optimal frequencies for electric stimulation using medium-frequency alternating current.

OBJECTIVE: To determine the effect of single cycles of alternating current of various frequencies on sensory and motor thresholds and on relative thresholds (motor threshold/sensory threshold). DESIGN: Repeated-measures design. SETTING: Laboratory setting. PARTICIPANTS: University student and staff volunteers (N=16; mean age, 34y). INTERVENTIONS: Single cycles of sinewave frequencies between 1 and 35kHz were delivered at 50Hz. The frequencies were applied in a random order. MAIN OUTCOME MEASURES: The motor and sensory thresholds were recorded at each applied frequency. RESULTS: Both sensory and motor thresholds showed a smooth decrease to a minimum at approximately 3kHz. The relative threshold reached a minimum close to 9kHz. Comparison with previous studies showed that although absolute thresholds reach a minimum at a frequency that depends on electrode size, the frequency at which the relative threshold is a minimum was independent of electrode size and independent of whether the stimulus was applied as single pulses or in burst mode. CONCLUSIONS: The optimal frequency for transcutaneous stimulation using medium-frequency alternating current depends on the outcome measure used. It would therefore be desirable for clinical stimulators to provide a selection of carrier frequencies.

Adult↗