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PubMed2007

Age of acquisition persists as the main factor in picture naming when cumulative word frequency and frequency trajectory are controlled.

The aim of this study was to address the effect of objective age of acquisition (AoA) on picture-naming latencies when different measures of frequency (cumulative and adult word frequency) and frequency trajectory are taken into account. A total of 80 Spanish participants named a set of 178 pictures. Several multiple regression analyses assessed the influence of AoA, word frequency, frequency trajectory, object familiarity, name agreement, image agreement, image variability, name length, and orthographic neighbourhood density on naming times. The results revealed that AoA is the main predictor of picture-naming times. Cumulative frequency and adult word frequency (written or spoken) appeared as important factors in picture naming, but frequency trajectory and object familiarity did not. Other significant variables were image agreement, image variability, and neighbourhood density. These results (a) provide additional evidence of the predictive power of AoA in naming times independent of word-frequency and (b) suggest that image variability and neighbourhood density should also be taken into account in models of lexical production.

Adult↗

PubMed2005

Detection, direction discrimination, and off-frequency interference of center-frequency modulations and glides for vowel formants.

Vowels are mainly classified by the positions of peaks in their frequency spectra, the formants. For normal-hearing subjects, change detection and direction discrimination were measured for linear glides in the center frequency (CF) of formantlike sounds. A CF rove was used to prevent subjects from using either the start or end points of the glides as cues. In addition, change detection and starting-phase (start-direction) discrimination were measured for similar stimuli with a sinusoidal 5-Hz formant-frequency modulation. The stimuli consisted of single formants generated using a number of different stimulus parameters including fundamental frequency, spectral slope, frequency region, and position of the formant relative to the harmonic spectrum. The change detection thresholds were in good agreement with the predictions of a model which analyzed and combined the effects of place-of-excitation and temporal cues. For most stimuli, thresholds were approximately equal for change detection and start-direction discrimination. Exceptions were found for stimuli that consisted of only one or two harmonics. In a separate experiment, it was shown that change detection and start-direction discrimination of linear and sinusoidal formant-frequency modulations were impaired by off-frequency frequency-modulated interferers. This frequency modulation detection interference was larger for formants with shallow than for those with steep spectral slopes.

Auditory Threshold↗

PubMed2006

Coherence detection: effects of frequency, frequency uncertainty, and onset/offset delays.

The detectability of a sequence of equal-frequency (coherent) tonal components embedded in random, multiburst maskers was evaluated. The masker was comprised of tonal components located in a time-by-frequency spectrogram with eight 30 ms time columns and 29 frequency rows ranging logarithmically from 200 to 5000 Hz. The probability that a tone occurred in any one cell of the spectrogram, p, was the independent variable. The signal and masker components were of equal duration and equal level. Using a yes/no procedure, threshold values of p were estimated for five signal frequencies (220, 445, 1000, 2245, 4490 Hz) and when the signal frequency was random. Thresholds were worst for the random-frequency signal and best for the fixed 1000 Hz signal. In additional conditions, the value of p was fixed and the signal components were delayed relative to the masker components. A 1 ms delay provided better sensitivity (d' grew from 0.5 to 1) for all but the lowest signal frequency tested. An analysis of no-signal trials revealed that false alarm rates were higher when components falling at the signal frequency were consecutive than when they were distributed across bursts. Thus, coherence rather than total energy at the signal frequency is important for signal detection.

Acoustic Stimulation↗

PubMed1995

Effects of carrier frequency, modulation rate, and modulation waveform on the detection of modulation and the discrimination of modulation type (amplitude modulation versus frequency modulation).

Initially, psychometric functions were measured for the detection of amplitude modulation (AM) or frequency modulation (FM), using a two-alternative forced-choice (2AFC) task. Carrier frequencies were 125, 1000, and 6000 Hz, and modulation rates were 2, 5, and 10 Hz. For the two lower carrier frequencies, FM detection tended to be best at the lowest modulation rate while AM detection was best at the highest rate. For the 6000-Hz carrier, both AM and FM detection tended to be poorest at the lowest modulation rate. Then, pairs of values of AM and FM were selected that would be equally detectable, and psychometric functions were measured for the discrimination of AM from FM, again in a 2AFC task. For carrier frequencies of 125 and 1000 Hz, the ability to discriminate AM from FM was always poorest at the highest modulation rate (10 Hz); at this rate some subjects were essentially unable to discriminate AM from FM when the detectability of the modulation was relatively low (d' of 1.16 and below). For a modulation rate of 2 Hz, and when the detectability of the modulation was moderate (d' up to about 2), some subjects discriminated the type of modulation rate varied across subjects, but there was still a trend for poorer discrimination of modulation type at the highest modulation rate. It is suggested that FM detection at a 10-Hz modulation rate is based largely on changes in excitation level for all carrier frequencies. For a 2-Hz modulation rate, and for the two lowest carrier frequencies, an extra mechanism, possibly based on phase locking, may play a role in the detection and discrimination of FM. This mechanism may be ineffective at modulation rates above about 5 Hz because the stimuli spend insufficient time at frequency extremes. To check on this, psychometric functions were measured for the detection of FM and AM using quasitrapezoidal modulation with a rate of five periods per second and carriers of 250, 1000, and 6000 Hz. This produced improvements in performance relative to that obtained with 5-Hz sinusoidal modulation and, for the two lower carrier frequencies only, the improvements were markedly greater for FM than for AM detection. This is consistent with the idea that the use of of phase-locking information depends on the time that the stimuli spend at frequency extremes.

Auditory Perception↗

PubMed1999

Effects of activation frequency and force on low-frequency fatigue in human skeletal muscle.

No comparison of the amount of low-frequency fatigue (LFF) produced by different activation frequencies exists, although frequencies ranging from 10 to 100 Hz have been used to induce LFF. The quadriceps femoris of 11 healthy subjects were tested in 5 separate sessions. In each session, the force-generating ability of the muscle was tested before and after fatigue and at 2, approximately 13, and approximately 38 min of recovery. Brief (6-pulse), constant-frequency trains of 9.1, 14.3, 33.3, and 100 Hz and a 6-pulse, variable-frequency train with a mean frequency of 14.3 Hz were delivered at 1 train/s to induce fatigue. Immediately postfatigue, there was a significant effect of fatiguing protocol frequency. Muscles exhibited greater LFF after stimulation with the 9.1-, 14.3-, and variable-frequency trains. These three trains also produced the greatest mean force-time integrals during the fatigue test. At 2, approximately 13, and approximately 38 min of recovery, however, the LFF produced was independent of the fatiguing protocol frequency. The findings are consistent with theories suggesting two independent mechanisms behind LFF and may help identify the optimal activation pattern when functional electrical stimulation is used.

Adult↗

PubMed2006

Frequency modulation between low- and high-frequency components of the heart rate variability spectrum.

Interactions among physiological mechanisms are abundant in biomedical signals, and they may exist to maintain efficient homeostasis. For example, sympathetic and parasympathetic neural activities interact to either elevate or depress the heart rate to maintain homeostasis. There has been considerable effort devoted to developing algorithms that can detect interactions between various physiological mechanisms. However, methods used to detect the presence of interactions between the sympathetic and parasympathetic nervous systems, to take one example, have had limited success. This may be because interactions in physiological systems are non-linear and non-stationary. The goal of this work was to identify non-linear interactions between the sympathetic and parasympathetic nervous systems in the form of frequency and amplitude modulations in human heart-rate data (n=6). To this end, wavelet analysis was performed, followed by frequency analysis of the resultant wavelet decomposed signals in several frequency brackets we define as: very low frequency (f<0.04 Hz), low frequency (0.04-0.15 Hz) and high frequency (0.15-0.4 Hz). Our analysis suggests that the high-frequency bracket is modulated by the low-frequency bracket in the heart rate data obtained in both upright and sitting positions. However, there was no evidence of amplitude modulation among these frequencies.

Algorithms↗

PubMed2006

The effects of root frequency, word frequency, and length on the processing of prefixed English words during reading.

Two experiments were performed to investigate the roles of root morpheme frequency and word frequency in the encoding of prefixed words in sentence context. Two alternative words, which were equated on other indices but differed with respect to either root morpheme frequency or word frequency, were embedded in the same sentence frame. In Experiment 1, there was a significant root morpheme frequency effect on gaze duration but only a marginal word frequency effect. Post hoc analyses indicated that word length influenced both effects, with word frequency effects predominating for shorter words and root morpheme effects predominating for longer words. In Experiment 2, word length was also manipulated. There was a significant root frequency effect for longer prefixed words and a significant word frequency effect for shorter prefixed words. The results were best explained by a dual-route model (with competing whole-word access and compositional routes), in which increasing word length inhibited the whole-word process, relative to the compositional route.

Eye Movements↗

PubMedDate not supplied

[Modulated extremely high frequency electromagnetic radiation of low intensity activates or inhibits respiratory burst in neutrophils depending on modulation frequency].

The influence of low-intensity modulated electromagnetic radiation of extremely high frequencies (EHF EMR) on synergistic reaction of calcium ionophore A23187 and phorbol ester PMA in activation of the respiratory burst of the peritoneal neutrophils of mice line NMRI was investigated. The production of reactive oxygen species by the neutrophils was estimated by luminol-dependent chemiluminescence technique. The cells were irradiated in the far field zone of the channel radiator for 20 min in the presence of A23187 and then were activated by PMA after switching off the irradiation. It was shown, that continuous EHF EMR (50 microW/cm2) inhibited quasi-resonantly the synergistic reaction. The maximum effect was about 25% at carrier frequency of 41.95 GHz. Modulated radiation with carrier frequency of 41.95 GHz and modulation frequency of 1 Hz activated the synergistic reaction, but at modulation frequencies of 0.1, 16 and 50 Hz inhibited one. At fixed modulation frequency of 1 Hz the nonlinear dependence of the effect on the carrier frequency was found. The synergistic reaction was activated in the frequency range of 41.95-42.05 GHz and was inhibited at the frequencies of 41.8-41.9 GHz. The effect was observed only at raised intracellular free calcium concentration and at calcium fluxes through plasma membrane. The obtained results prove the possibility of control over cell functioning by low-intensity modulated EHF EMR, presumably, manipulating by connected systems of enzyme reactions.

Animals↗

PubMed2004

Frequency of kdr gene in house fly field populations: correlation of pyrethroid resistance and kdr frequency.

The frequency of the L1014 F kdr mutation was determined in 14 field populations of house flies, Musca domestica L., with resistance factors at LD50 for pyrethrin/piperonyl butoxide and bioresmethrin/piperonyl butoxide from 4 to 29 and 2 to 98, respectively. A polymerase chain reaction test for identifying kdr homo- or heterozygote house flies was used to determine the frequency of kdr. The L1014 F allele was found in all populations tested. The frequency of kdr in the field populations was high and varied from 0.46 to 0.99. Eleven of the populations were in Hardy-Weinberg equilibrium, whereas two strains had higher number of heterozygotes than expected, indicating a possible heterozygote advantage. The frequency of kdr was strongly correlated with the reduced mortality observed in the bioassays with pyrethrum and bioresmethrin synergized by piperonyl butoxide. This indicates that kdr is a major mechanism for pyrethroid resistance in these field populations. Five field populations had resistance factors >25 and >10 for bioresmethrin/piperonyl butoxide and pyrethrin/piperonyl butoxide, respectively. The frequencies of kdr in these five populations varied from 0.89 to 0.99. The frequencies of kdr in the field populations showing no or a low level of resistance had frequencies of kdr from 0.46 to 0.75, which indicates that the L1014 F kdr allele is a fully recessive genetic trait in house flies. We have shown that the molecular diagnostic PASA method to determine the resistance phenotypes and the frequency of kdr is a powerful tool, which could be used to get information to make recommendations about pest and resistance management.

Alleles↗

PubMed2004

Variation of female frequency and cytoplasmic male-sterility gene frequency among natural gynodioecious populations of wild radish (Raphanus sativus L.).

In gynodioecious plant populations, sex determination often involves both cytoplasmic male-sterility (CMS) genes and specific nuclear genes that restore male function. How gynodioecy is maintained under the joint dynamics of CMS and restorer genes remains controversial. Although many theoretical models deal with interactions between CMS genes and restorer genes with sexual phenotypes and predict changes in their frequencies, it is difficult to observe the frequencies because no molecular markers have been established for either CMS or restorer genes in well-studied gynodioecious plants. This is the first report of the frequency of a CMS gene determined using a molecular marker in natural populations of a gynodioecious plant. Using a set of CMS gene-specific polymerase chain reaction primers, we compared female and CMS gene frequencies in 18 natural populations of Raphanus sativus. Female frequency was relatively low, ranging from 0 to 0.21. In contrast, the CMS gene frequency was highly variable among populations, ranging from 0 to 1. Estimated restorer gene frequency seemed less variable than observed CMS gene frequency, probably due to higher gene flow than in the CMS gene. Genetic drift may play a role in maintaining high variability of the CMS gene, although other possibilities are not excluded.

DNA Primers↗

PubMed1990

Frequency, tidal volume, and mean airway pressure combinations that provide adequate gas exchange and low alveolar pressure during high frequency oscillatory ventilation in rabbits.

We studied healthy and saline lavaged rabbits during high frequency oscillatory ventilation to determine what combination of frequency (f), tidal volume (Vt), and mean airway pressure (Paw) produced the lowest peak-to-peak alveolar pressure amplitude (Palv) and physiologic blood gas tensions. Sinusoidal volume changes were delivered through a tracheostomy by a piston pump driven by a linear motor. Tracheal pressure amplitude (Ptr) was measured through a tracheal catheter and alveolar pressure amplitude was measured in a capsule glued to the right lower lobe. PaO2, PaCO2, Ptr, and Palv were measured at the following settings: FiO2 = 0.5, frequency 2-28 Hz, Vt 1-3 mL/kg (50 150% dead space) and Paw 5-15 cm H2O. Many combinations of frequency and Vt resulted in the same PaO2 and PaCO2. Paw had a large effect on Palv and minimal effect on blood gas tensions. In lavaged rabbits, the composite variable f x Vt2 described the trends in Palv and blood gas tensions. As the product of f x Vt2 increased, PaO2 initially increased and then decreased, whereas PaCO2 decreased and Palv increased. No single combination of frequency, Vt and Paw simultaneously provided the lowest Palv and physiologic blood gas tensions. Adequate blood gas tensions and low Palv were obtained at frequencies less than 12 Hz, a Vt of 2 mL/kg and a Paw of 10 cm H2O. In healthy and lavaged rabbits PaO2 increased and PaCO2 decreased as frequency increased at lower Vt.PaO2 decreased as frequency increased at higher Vt in lavaged rabbits only. Palv tended to be greater in lavaged rabbits.

Airway Resistance↗

PubMed1999

Variable-frequency trains offset low-frequency fatigue in human skeletal muscle.

Variable-frequency trains that exploit the catchlike property of skeletal muscle can augment force production in fatigued skeletal muscle. The present study is the first to examine the effect of such trains during recovery. The quadriceps femoris muscles of 12 healthy individuals were fatigued using six-pulse, 14.3-Hz trains delivered at a rate of 1/s for 3 min. The force-generating ability of the muscle was tested with several constant-frequency trains (8.3-100 Hz) and a variable-frequency train before and after fatigue and at 2, approximately 13, and approximately 38 min of recovery. The variable-frequency train produced significant augmentation of force versus the best constant-frequency train (12.5 Hz) in acute fatigue and during recovery. The fatiguing protocol also induced low-frequency fatigue (LFF); the time courses of the degree of LFF and the amount of variable-frequency train force augmentation were inversely related (r = 0.629; F = 38.024; P </= 0.001), suggesting a common mechanism between the two phenomena. These results suggest that clinical use of variable-frequency trains (e.g., functional electrical stimulation) will enable the muscle to generate more force during acute fatigue and offset, at least partially, the long-term effects of LFF.

Adult↗

PubMed2001

Variation in motor threshold with frequency using kHz frequency alternating current.

We investigated the frequency dependence of motor thresholds over the frequency range 1 kHz to 25 kHz. Alternating current (AC), ramped in intensity, was applied transcutaneously, and the induced wrist extensor torque was measured. Plots of log torque versus stimulus voltage were used to accurately determine thresholds. Three kinds of sinusoidal AC stimuli were compared: continuous, 10 ms bursts at 50 Hz, and 50-Hz single-cycle. Differences were attributed to summation of subthreshold depolarizations. The variation in relative thresholds (continuous/single-cycle and burst/single-cycle) indicates that summation occurs more efficiently at higher kHz frequencies. The observed frequency and waveform dependence provides evidence for high-frequency nerve fiber firing rates and fiber dropout when continuous or modulated AC is used, with the effects increasing with AC frequency. The form of the motor response evoked at high frequencies has features that suggest that frequencies above 10-kHz have little or no useful clinical role in rehabilitation procedures.

Adult↗

PubMed1985

An HRP-study of the frequency-place map of the horseshoe bat cochlea: morphological correlates of the sharp tuning to a narrow frequency band.

The frequency-place map of the horseshoe bat cochlea was studied with the horseradish peroxidase (HRP) technique involving focal injections into various, physiologically defined regions of cochlear nucleus (CN). The locations of labeled spiral ganglion cells and their termination sites on inner hair cells of the organ of Corti from injections into CN-regions responsive to different frequencies were analyzed in three dimensional reconstructions of the cochlea. Horseshoe bats from different geographical populations were investigated. They emit orientation cells with constant frequency (CF) components around 77 kHz (Rhinolophus rouxi from Ceylon) and 84 kHz (Rhinolophus rouxi from India) and their auditory systems are sharply tuned to the respective CF-components. The HRP-map shows that in both populations: the frequency range around the CF-component of the echolocation signal is processed in the second half-turn of the cochlea, where basilar membrane (BM) is not thickened, secondary spiral lamina (LSS) is still present and innervation density is maximal; frequencies more than 5 kHz above the CF-component are processed in the first half-turn, where the thickened BM is accompanied by LSS and innervation density is low; frequencies below the spectral content of the orientation call are represented in apical turns showing no morphological specializations. The data demonstrate that the cochlea of horseshoe bats is normalized to the frequency of the individual specific CF-component of the echolocation call. The HRP-map can account for the overrepresentation of neurons sharply tuned to the CF-signal found in the central auditory system. A comparison of the HRP-map with a map derived with the 'swollen nuclei technique' following loud sound exposure (Bruns 1976b) reveals that the latter is shifted towards cochlear base by about 4 mm. This discrepancy warrants a new interpretation of the functional role of specialized morphological structures of the cochlea within the mechanisms giving rise to the exceptionally high frequency selectivity of the auditory system.

Animals↗

PubMed2005

[Frequency specific auditory evoked responses. Experiments on stimulus polarity, sweep frequency, stimulus duration, notched-noise masking level, and threshold estimation in volunteers with normal hearing].

Auditory evoked responses to tone-pips in notched-noise provide frequency specific estimations of thresholds. Most often, test frequencies are 0.5-4 kHz. Thresholds are expected to match with a high degree to behavioral thresholds. However, only few studies are available containing data on stimulus and averaging parameters, especially at a test frequency of 0.25 kHz. In order to find "optimal" parameters for a widely used device (Nicolet Spirit Version 1.6), we designed five experiments on stimulus polarity (Exp.I), sweep frequency (Exp.II), stimulus duration (Exp.III), notched noise level (Exp.IV), and threshold estimation (Exp.V). The experiments also included a low test frequency of 0.25 kHz. These experiments were applied to 29 healthy volunteers (n=29, aged 20-41 years with normal hearing and no history of illness of the ear). We found that alternating stimulus polarity and a sweep frequency of 43.5/s evoked responses that were highest with respect to amplitudes (0.2-0.4 mV) and correlations (0.49-0.91). A novel finding of the study was that the highest amplitudes and correlations could be achieved if stimulus durations and notched-noise-levels were specifically adjusted to the test frequencies (stimulus durations 0.25 kHz: 4 ms, 0.5 Hz: 2 ms, 1-4 kHz: 1 ms, notched-noise-levels 0.25-0.5 Hz: +10 dB, 1-4 kHz: +/-0 dB). Deviations from behavioral thresholds did not exceed +/-5 dB in 93% of the measures. The results indicate that frequency specific auditory evoked responses provide reliable threshold estimations. Future experiments are required to confirm the threshold deviations for hard of hearing individuals.

Acoustic Stimulation↗

PubMed1994

Exposure to low frequency noise during rearing induces spongiform lesions in gerbil cochlear nucleus: high frequency exposure does not.

Spongiform lesions of the gerbil cochlear nucleus are reduced in number and extent by rearing in acoustic isolation compared with rearing while exposed to normal colony low-frequency background noise. This study tested whether rearing under exposure to noise bands of moderate intensity would increase the number and extent of cochlear nucleus spongiform lesions. Gerbils were reared from weaning to young adulthood in acoustic isolation chambers while continually exposed to moderately intense bands of either high frequency or low frequency noise. Exposure to low frequency noise resulted in lesion number and area densities that were more than twice those seen in gerbils exposed to high frequency noise. Lesion extent in the low frequency group was similar to that in colony-reared gerbils; lesion extent in the high frequency group was similar to gerbils reared in acoustic isolation. Comparisons within the posterior ventral cochlear nucleus revealed that the differences in lesion extent were most pronounced in the middle and dorsal-medial portions, the regions that are most responsive to middle and high frequencies. These finding suggest that the regional restriction of spongiform lesions within the cochlear nucleus does not have a tonotopic basis.

Acoustic Stimulation↗

PubMed2004

Frequency discrimination at different frequency levels as indexed by electrophysiological and behavioral measures.

The present study systematically compared the neural and behavioral accuracy of discriminating a frequency change ("deviant") in a repetitive tone ("standard") across a frequency range of 250-4000 Hz. The sound structure (pure sinusoidal vs. harmonically rich tones) and the magnitude of frequency change (2.5%, 5%, 10%, 20%) were also varied. The accuracy of neural frequency-change detector was determined by comparing the auditory event-related potentials (ERP) elicited by deviant and standard stimuli in the absence of attention. In a separate behavioral task, subjects were to indicate when they noticed a frequency change. The ranges of the across-subject means of ERP parameters across the conditions were: the mismatch negativity (MMN) amplitude -0.9 to -4.9 microV, latency 125-218 ms, the P3a amplitude 0.3-3.2 microV, latency 239-304 ms. The ERP latency was shortest for the standard-stimulus frequency from 1000 to 2000 Hz suggesting that automatic frequency discrimination was the most accurate in that range. The ERP latencies and amplitudes correlated with the hit rate (HR) and reaction time (RT), with highest correlation found between the MMN amplitude and the HR (r=0.8). The harmonical tones elicited MMN and P3a with shorter latencies and larger amplitudes, than did pure sinusoidal tones in all frequency bands. The results may have implication to pitch-perception theories.

Acoustic Stimulation↗

PubMed2006

Difference frequency and its harmonic emitted by microbubbles under dual frequency excitation.

Vibro-acoustography is an elasticity imaging method that uses two ultrasound beams of slightly different frequency to excite an object and detects the resulting acoustic emission (AE) at the difference frequency. This method is especially sensitive to bubbles due to their nonlinearity. This study explores the harmonic acoustic emission (HAE) at twice the difference frequency emitted from bubbles. A perturbation method based on the dynamic bubble equation is used to derive the AE and HAE from a single bubble excited by dual frequency waves. Simulation shows that HAE is generated only by microbubbles whose resonant frequencies match the incident ultrasound frequencies. In contrast, AE is more sensitive to resonance at the difference frequency, which is relevant to sub-millimeter bubbles. This finding was confirmed by experiments where HAE was produced from Optison microbubbles, but not from larger air bubbles which are off resonance at the incident ultrasound frequency. In conclusion, harmonic acoustic emission is present for microbubbles. It is very sensitive to the size of the bubble and may be used for selective detection of microbubbles.

Albumins↗