Sensory cues for the gradual frequency fall responses of the gymnotiform electric fish, Rhamphichthys rostratus

The sensory cues for a less known form of frequency shifting behavior, gradual frequency falls, of electric organ discharges (EODs) in a pulse-type gymnotiform electric fish, Rhamphichthys rostratus, were identified. We found that the gradual frequency fall occurs independently of more commonly observed momentary phase shifting behavior, and is due to perturbation of sensory feedback of the fish's own EODs by EODs of neighboring fish. The following components were identified as essential features in the signal mixture of the fish's own and the neighbor's EOD pulses: (1) the neighbor's pulses must be placed within a few millisecond of the fish's own pulses, (2) the neighbor's pulses, presented singly at low frequencies (0.2–4 Hz), were sufficient, (3) the frequency of individual pulse presentation must be below 4 Hz, (4) amplitude modulation of the sensory feedback of the fish's own pulses induced by such insertions of the neighbor's pulses must contain a high frequency component: sinusoidal amplitude modulation of the fish's own EOD feedback at these low frequencies does not induce gradual frequency falls. Differential stimulation across body surfaces, which is required for the jamming avoidance response (JAR) of wave-type gymnotiform electric fish, was not necessary for this behavior. We propose a cascade of high-pass and low-pass frequency filters within the amplitude processing pathway in the central nervous system as the mechanism of the gradual frequency fall response.Abbreviations EOD electric organ discharge - f frequency of EOD or pacemaker command signal - JAR jamming avoidance response - S ₁ stimulus mimicking fish's own EOD - f ₁ frequency of S₁ - S ₂ stimulus mimicking neighbor's EOD - f ₂ frequency of S₂     

Subthreshold activation of spinal motoneurones in the stretch reflex: experimental data and modeling

Responses of gastrocnemius–soleus motoneurones to stretches of the homonymous muscles were recorded intrasomatically in decerebrate cats; changes of membrane potential (MP) were evoked by smoothed trapezoid stretches of the muscles. Amplitudes of separate excitatory postsynaptic potentials (EPSPs) were defined via differences between values of MP at the end and beginning of the positive derivative waves, which were also used as basic elements in the model of the excitatory postsynaptic currents (EPSCs). EPSCs were assumed to be transformed into EPSPs by low-pass filtering properties of the somatic membrane; parameters of the filtering were firstly defined from analysis of Ia EPSP in the same cell and then were applied in model P _m0. The model showed unsatisfactory quality in tracking slow components of MP; to overcome the disadvantage there was proposed model P _m1 based on addition to P _m0 the difference between two low-pass filtered signals MP and P _m0 (the cutoff frequency 10 or 20 Hz). An overestimation of EPSPs’ amplitudes was corrected in model P _m2. The mismatch in tracking slow changes of MP was assumed to be connected with summation of a great number of low-amplitude EPSPs generated at distal dendrites; information about waveform of separate EPSPs could disappear in this process. One can speculate that slow components of membrane depolarization at least partly are linked with the persistent inward currents in dendrites; variable and, sometimes, too fast decays in EPSPs seem to reflect inhibitory synaptic influences.     

Frequency limitations of the two-point central difference differentiation algorithm

A two-point central difference algorithm is often used to calculate the derivative of a function. This estimate is only valid over a limited frequency range. Therefore, the algorithm can be modeled as an ideal differentiator in series with a low-pass filter. The filter cutoff frequency is a function of the time between the points. We discuss the accuracy and limitations of using this algorithm on human saccadic eye movement data. To calculate the velocity of saccadic eye movements the algorithm should have a cutoff frequency of 74 Hz or above.     

Amputee locomotion: Frequency content of prosthetic vs. intact limb vertical ground reaction forces during running and the effects of filter cut-off frequency

Compared to intact limbs, running-specific prostheses have high resonance non-biologic materials and lack active tissues to damp high frequencies. These differences may lead to ground reaction forces (GRFs) with high frequency content. If so, ubiquitously applying low-pass filters to prosthetic and intact limb GRFs may attenuate veridical high frequency content and mask important and ecologically valid data from prostheses. To explore differences in frequency content between prosthetic and intact limbs we divided signal power from transtibial unilateral amputees and controls running at 2.5, 3.0, and 3.5 m/s into Low (<10 Hz), High (10–25 Hz), and Non-biologic (>25 Hz) frequency bandwidths. Faster speeds tended to reduce the proportion of signal power in the Low bandwidth while increasing it in the High and Non-biologic bandwidths. Further, prostheses had lower proportions of signal power at the High frequency bandwidth but greater proportions at the Non-biologic bandwidth. To evaluate whether these differences in frequency content interact with filter cut-offs and alter results, we filtered GRFs with cut-offs from 1 to 100 Hz and calculated vertical impact peak (VIP). Changing cut-off had inconsistent effects on VIP across speeds and limbs: Faster speeds had significantly larger changes in VIP per change in cut-off while, compared to controls, prosthetic limbs had significantly smaller changes in VIP per change in cut-off. These findings reveal differences in GRF frequency content between prosthetic and intact limbs and suggest that a cut-off frequency that is appropriate for one limb or speed may be inappropriate for another.     

The influence of extremely weak alternating magnetic fields on the regeneration of planarians and the gravitropic response of plants

The influence of extremely weak alternating magnetic fields (EW AMF) directed collinearly to the static Earth magnetic field on the rate of regeneration of planarians and the rate of gravitropic response in the stem segments of flax has been studied. The value of bioeffects of EW AMF is determined by the parameter γB _AC/f, where γ is the gyromagnetic ratio of the magnetic moments induced by the orbital movements of electrons in atoms, and B _AC and f correspond to magnetic induction and frequency of the alternating magnetic component. It was shown that the magnitude of bioeffects depends on the amplitude (at fixed 1000 Hz — frequency) and frequency (at fixed 192 nT — amplitude) of the alternating component. Maxima of bioeffects are observed at γB _AC/f = 0.9; 2.75, and minor maxima γB _AC/f = 4.5; 6.1. The bioeffects are absent at γB _AC/f =1.8, 3.8, 5.3, 6.7. The positions of the maxima and minima of bioeffects correspond to the theoretical prediction (at γ = 14000 Hz/μT). Primary targets for the EW AMF of this type are the magnetic moments induced by the orbital movements of electrons in atoms.     

The ontogeny of the locomotor wave in sevruga fish (Acipenser stellatus Pall.)

Continuous filming of the swimming movements of sevruga prelarvae (Acipenser stellatus Pall.) was performed over the first to the fifteenth post-hatching days. These data were used to determine three locomotor characteristics: {f(v, θ), A(v, θ), w(v, θ)} where f is the frequency of the transverse oscillations; A is the amplitude of the tail fin movements; w is the speed of the locomotor wave; v is the speed of the locomotion; and θ is the number of days during which the filming was carried out. In addition, the comparison of two characteristics was performed. These are the step length L(v, θ) and the wavelength λ(v, θ), where L ≡ vT is the distance that a fish covers in time T ≡ 1/f and λ is λ ≡ wT. The results led to the conclusion that the prelarva swimming movements achieve the carangiform mode by the end of the second week. This is characteristic of adults and coincides with the beginning of external feeding. The mode is represented by an equation that follows from the generalized Bainbridge’s law: f = f ₀ + f ₁ v/H. The equation includes one anatomical parameter H of total length and two kinematic parameters f ₀ and f ₁, which can be calculated by the linear approximation method. These are the kinematic parameters that are changed in the early ontogenesis when 1 ≤ θ ≤ 15. However, the parameters become stable when θ ≥ 15. This means that the parameter values are constant and similar to those of adult fish. The similar properties of stabilization and variability have the kinematic parameters of other locomotor characteristics.

     

Hypoxic cardiorespiratory reflexes in the facultative air-breathing fish jeju (Hoplerythrinus unitaeniatus): role of branchial O2 chemoreceptors

In one series of experiments, heart frequency (f _H), blood pressure (P _a), gill ventilation frequency (f _R ), ventilation amplitude (V _AMP) and total gill ventilation (V _TOT) were measured in intact jeju (Hoplerythrinus unitaeniatus) and jeju with progressive denervation of the branchial branches of cranial nerves IX (glossopharyngeal) and X (vagus) without access to air. When these fish were submitted to graded hypoxia (water PO₂ ~140, normoxia to 17 mmHg, severe hypoxia), they increased f _R , V _AMP, V _TOT and P _a and decreased f _H. In a second series of experiments, air-breathing frequency (f _RA), measured in fish with access to the surface, increased with graded hypoxia. In both series, bilateral denervation of all gill arches eliminated the responses to graded hypoxia. Based on the effects of internal (caudal vein, 150 μg NaCN in 0.2 mL saline) and external (buccal) injections of NaCN (500 μg NaCN in 1.0 mL water) on f _R , V _AMP, V _TOT, P _a and f _H we conclude that the O₂ receptors involved in eliciting changes in gill ventilation and associated cardiovascular responses are present on all gill arches and monitor the O₂ levels of both inspired water and blood perfusing the gills. We also conclude that air breathing arises solely from stimulation of branchial chemoreceptors and support the hypothesis that internal hypoxaemia is the primary drive to air breathing.     

Influence of sodium concentration on changes of membrane capacitance associated with the electrogenic ion transport by the Na,K-ATPase

Electrogenic ion transport by the Na,K-ATPase was investigated in a model system of protein-containing membrane fragments adsorbed to a lipid bilayer. Transient Na⁺ currents were induced by photorelease of ATP from inactive caged ATP. This process was accompanied by a capacitance change of the membrane system. Two methods were applied to measure capacitances in the frequency range 1 to 6000 Hz. The frequency dependent capacitance increment, ΔC, was of sigmoidal shape and decreased at high frequencies. The midpoint frequency, f ₀, depended on the ionic strength of the buffer. At 150 mm NaCl f ₀ was about 200 Hz and decreased to 12 Hz at high ionic strength (1 M). At low frequencies (f≪f ₀) the capacitance increment became frequency independent. It was, however, dependent on Na⁺ concentration and on the membrane potential which was generated by the charge transferred. A simple model is presented to analyze the experimental data quantitatively as a function of two parameters, the capacitance of the adsorbed membrane fragments, C _P, and the potential of maximum capacitance increment, ψ ₀. Below 5 mm Na⁺ a negative capacitance change was detected which may be assigned to electrogenic Na⁺ binding to cytoplasmic sites. It could be shown that the results obtained by experiments with the presented alternating current method contain the information which is determined by current-relaxation experiments with cell membranes. Received: 3 November 1997 / Revised version: 19 February 1998 / Accepted: 21 February 1998     

Effects of low-pass filter combinations on lower extremity joint moments in distance running

Inverse dynamics is a standard tool in biomechanics, which requires low-pass filtering of external force and kinematic signals. Unmatched filtering procedures are reported to affect joint moment amplitudes in high impact movements, like landing or cutting, but are also common in the analysis of distance running. We analyzed the effects of cut-off frequencies in 94 rearfoot runners at a speed of 3.5 m/s. Additionally, we investigated whether the evaluation of footwear interventions is affected by the choice of cut-off frequencies. We performed 3D inverse dynamics for the hip, knee and ankle joints using different low-pass filter cut-off frequency combinations for a recursive fourth-order Butterworth filter. We observed fluctuations of joint moment curves in the first half of stance, which were most pronounced for the most unmatched cut-off frequency combination (kinematics: 10 Hz; ground reaction forces (GRFs): 100 Hz) and for more proximal joints. Peak sagittal plane hip joint moments were altered by 94% on average. We observed a change in the ranking of subjects based on joint moment amplitude. We found significant (p < 0.001) footwear by cut-off frequency combination interaction effects for most peak joint moments. These findings highlight the importance of cut-off frequency choice in the analysis of joint moments and the assessment of footwear interventions in distance running. Based on our results, we propose to use matched cut-off frequencies around 20 Hz in order to avoid large artificial fluctuations in joint moment curves while at the same time avoiding a severe removal of physiological high-frequency signal content from the GRF signals.     

Poroelasticity of cartilage at the nanoscale

Atomic-force-microscopy-based oscillatory loading was used in conjunction with finite element modeling to quantify and predict the frequency-dependent mechanical properties of the superficial zone of young bovine articular cartilage at deformation amplitudes, δ, of ∼15 nm; i.e., at macromolecular length scales. Using a spherical probe tip (R ∼ 12.5 μm), the magnitude of the dynamic complex indentation modulus, |E^∗|, and phase angle, φ, between the force and tip displacement sinusoids, were measured in the frequency range f ∼ 0.2–130 Hz at an offset indentation depth of δ₀ ∼ 3 μm. The experimentally measured |E^∗| and φ corresponded well with that predicted by a fibril-reinforced poroelastic model over a three-decade frequency range. The peak frequency of phase angle, f_peak, was observed to scale linearly with the inverse square of the contact distance between probe tip and cartilage, 1/d², as predicted by linear poroelasticity theory. The dynamic mechanical properties were observed to be independent of the deformation amplitude in the range δ = 7–50 nm. Hence, these results suggest that poroelasticity was the dominant mechanism underlying the frequency-dependent mechanical behavior observed at these nanoscale deformations. These findings enable ongoing investigations of the nanoscale progression of matrix pathology in tissue-level disease.     

Quadriceps EMG frequency content following isometric lumbar extension exercise

A relationship exists between muscles of the lumbar spine and those of the lower extremity where the quadriceps become more inhibited after lumbar paraspinal. The purpose of this experiment was to compare surface electromyography (sEMG) total frequency content after lumbar paraspinal fatiguing exercise. Scope: 50 subjects performed fatiguing lumbar extension exercise indexed by downward shifts in median frequency calculated from lumbar paraspinal sEMG signal. Before and after each exercise set we recorded maximal, isometric knee extension torque and quadriceps central activation ratio (QI) using the superimposed burst technique while recording vastus lateralis sEMG. We calculated total frequency content of the sEMG signal (fEMG_TOTAL) as the area of the quadriceps sEMG frequency spectrum. Quadriceps fEMG_TOTAL decreased from baseline following the first and second exercise sets. There was no significant change in quadriceps sEMG median frequency among baseline and post-exercise measures. The change in fEMG_TOTAL was correlated with the change in QI following the first (r = ?0.41, P = 0.003) and second (r = ?0.32, P = 0.02) exercise sets. Conclusion: Quadriceps fEMG_TOTAL decreased following fatiguing lumbar extension exercise, in the absence of a significant change in quadriceps median frequency.     

Control of doppler shift compensation in the greater horseshoe bat,Rhinolophus ferrumequinum

Summary FlyingRhinolophus ferrumequinum lower the frequency of the constant frequency part (f _A ) of the emitted sounds in order to compensate for Doppler shifts caused by the flight speed. The echo frequency (f _E ) is kept constant within a frequency band of about 200 Hz, the center frequency of which is about 150 Hz above the average or resting frequency (f _R ) emitted by roosting bats shortly before take off. For the compensation they use a feedback control system in which the emission frequency is changed to hold the echo frequency at a criterion value. This feedback system was demonstrated by experiments with bats flying in an experimental wind tunnel and in a He-O₂-micture. In the wind tunnelRhinolophus lowers the emission frequency in order to compensate for Doppler shifts which are caused by the ground speed flown by the bat. In the He-O₂-mixtureRhinolophus compensates for Doppler shifts which correspond to the different sound speeds in the gas mixture.I would like to thank D. R. Griffin for his generous support and stimulating criticism. I express my appreciation to the New York Zoological Society for the use of its facilities and to R. Brown for technical assistance. The work was supported by grant number GB 7155 from the National Science Foundation to the New York Zoological Society. I also thank J. D. Pye for his suggestions.     

A new interpretation of P300 responses upon analysis of coherences

Previous studies on cognitive dynamics showed that oscillatory responses of P300 are composed of mainly delta and theta responses. In the present study, for the first time, the long-distance intra-hemispheric event related coherence (auditory oddball paradigm) and evoked coherence (simple sound) were compared in order to evaluate the effects of cognitive tasks on the long-distance coherences. Seventeen healthy subjects (8 female, 9 male) were included in the study. The coherence was analyzed for delta (1–3.5 Hz), theta (4–7.5 Hz) and alpha (8–13 Hz) frequency ranges for (F₃-P₃, F₄-P₄, F₃-T₇, F₄-T₈, F₃-O_1, F₄-O₂) electrode pairs. The coherence to target responses were higher than the non-target and simple auditory response coherence. This difference is significant for the delta coherence for both hemispheres and for theta coherences over the left hemisphere. The highest coherences were recorded at fronto-temporal locations for all frequency bands (delta, theta, alpha). Furthermore, fronto-parietal coherences were higher than the fronto-occipital coherences for all frequency bands (delta, theta, alpha).These results show that the fronto-temporal and fronto-parietal connections are most relevant for the identification of the target signal. This analysis open the way for a new interpretation of dynamic localization results during cognitive tasks.     

On the correlation dimension of optokinetic nystagmus eye movements: computational parameters, filtering, nonstationarity, and surrogate data

 We discuss the estimation of the correlation dimension of optokinetic nystagmus (OKN), a type of reflexive eye movement. Parameters of the time-delay reconstruction of the attractor are investigated, including the number of data points, the time delay, the window duration, and the duration of the signal being analyzed. Adequate values are recommended. Digital low-pass filtering causes the dimension to increase as the filter cutoff frequency decreases, in accord with a previously published prediction. The stationarity of the correlation dimension is examined; the dimension appears to decrease over the course of 120 s of continuous stimulation. Implications for the reliable estimation of the dimension are considered. Several surrogate data sets are constructed, based on both early (0–30 s) and late (100–130 s) OKN segments. Most of the surrogate data sets randomize some aspect of the original OKN, while maintaining other aspects. Dimensions are found for all surrogates and for the original OKN. Evidence is found that is consistent with some amount of deterministic and nonlinear dynamics in OKN. When this structure is randomized in the surrogate, the dimension changes or the dimension algorithm ceases to converge to a finite value. Implications for further analysis and modeling of OKN are discussed. Received: 30 August 1996/Accepted in revised form: 13 November 1996     

Modeling the Population Level Effects of an HIV-1 Vaccine in an Era of Highly Active Antiretroviral Therapy

First generation HIV vaccines may have limited ability to prevent infection. Instead, they may delay the onset of AIDS or reduce the infectiousness of vaccinated individuals who become infected. To assess the population level effects of such a vaccine, we formulate a deterministic model for the spread of HIV in a homosexual population in which the use of highly active antiretroviral therapy (HAART) to treat HIV infection is incorporated. The basic reproduction number R ₀ is obtained under this model. We then expand the model to include the potential effects of a prophylactic HIV vaccine. The reproduction number R _f is derived for a population in which a fraction f of susceptible individuals is vaccinated and continues to benefit from vaccination. We define f ^* as the minimum vaccination fraction for which R _f ≤1 and describe situations in which it equals the critical vaccination fraction necessary to eliminate disease. When R ₀ is large or an HIV vaccine is only partially effective, the critical vaccination fraction may exceed one. HIV vaccination, however, may still reduce the prevalence of disease if the reduction in infectiousness is at least as great as the reduction in the rate of disease progression. In particular, a vaccine that reduces infectiousness during acute infection may have an important public health impact especially if coupled with counseling to reduce risky behavior.     

Echolocation and obstacle avoidance in the hipposiderid batAsellia tridens

Summary The echolocation sounds of the hipposiderid batAsellia tridens consist of a constant frequency (cf) component followed by a frequency modulated (fm) terminal downward sweep of 19–21 kHz. The cf-part constitutes about 7/10 of the entire signal. In individual roosting animals the frequencies of the cf-part of consecutive sounds (resting frequency) is kept very constant but varies from bat to bat. In 18Asellia tridens resting frequencies between 111–124 kHz have been measured.The sound duration in roosting and free flying bats is between 7–10 ms. In the approach and terminal phase of bats landing on a perch or flying through obstacles, the sound duration is reduced and the repetition rate increased the nearer the bat approaches the target. At the end of the terminal phase sound durations of a minimum of 3 ms have been measured. Flying bats lower their emission frequency in order to compensate for Doppler shifts caused by the flight movement. The echofrequency is therefore kept constant about 150–200 Hz above the resting frequency.In flights through obstacles consisting of vertically stretched wires with different diameters, the bats were able to avoid wires down to a diameter of 0.065 mm whereas at 0.05 mm the percentage of flights without collisions is far below the chance level. The results demonstrate that the echolocation behavior of the hipposiderid batAsellia tridens does not differ fundamentally from that of rhinolophid bats. As a result, a new suggestion for categorization of bats producing cf-fm orientation sounds is put forward.Abbreviations cf constant frequency component - fm frequency modulated component - P probability of collision-free flights through an obstacle of ertically tretched wires - I interval between wires - D minimal diameter of a bat with folded wings; , angle at which a bat approaches an obstacle - f _A frequency of the cf-component of the emitted sound - f _E frequency of the cf-component of the echo - f _M frequency of the cf-component of the sounds recorded with the microphone - c speed of sound Supported by the Deutsche Forschungsgemeinschaft grant no. Schn 138/6-9We thank W. Hollerbach for technical assistance.     

Wavelet threshold based TDL and TDR algorithms for real-time ECG signal compression

In this paper, two novel and simple, target distortion level (TDL) and target data rate (TDR), Wavelet threshold based ECG compression algorithms are proposed for real-time applications. The issues on the use of objective error measures, such as percentage root mean square difference (PRD) and root mean square error (RMSE) as a quality measures, in quality controlled/guranteed algorithm are investigated with different sets of experiments. For the proposed TDL and TDR algorithm, data rate variability and reconstructed signal quality is evaluated under different ECG signal test conditions. Experimental results show that the TDR algorithm achieves the required compression data rate to meet the demands of wire/wireless link while the TDL algorithm does not. The compression performance is assessed in terms of number of iterations required to achieve convergence and accuracy, reconstructed signal quality and coding delay. The reconstructed signal quality is evaluated by correct diagnosis (CD) test through visual inspection. Three sets of ECG data from three different databases, the MIT-BIH Arrhythmia (mita) (F_s=360 Hz, 11 b/sample), the Creighton University Ventricular Tachyarrhythmia (cuvt) (F_s=250 Hz, 12 b/sample) and the MIT-BIH Supraventricular Arrhythmia (mitsva) (F_s=128 Hz, 10 b/sample), are used for this work. For each set of ECG data, the compression ratio (CR) range is defined. The CD value of 100% is achieved for CR ≤12, CR ≤ 8 and CR ≤ 4 for data from mita, cuvt and mitsva databases, respectively. The experimental results demonstrate that the proposed TDR algorithm is suitable for real-time applications.     

A comparison of the Schumacher with other functions for describing growth in pigs

This study was undertaken to introduce the Schumacher equation and compare it with established functions for describing growth in pigs. The relationship between live weight (LW) and cumulative feed intake was also investigated. A database was constructed from three independent trials in which LW, age and intake were measured from birth to 937 days. Three growth functions were used for analysis of growth versus age: Gompertz, Schumacher and Weibull; and the Richards and monomolecular equations were used for analysis of cumulative feed intake versus LW. The growth functions have different points of inflexion. Liveweight at inflexion is W_f/e for the Gompertz, where W_f is the final weight, W_f/e² for the Schumacher, and W_f − (W_f − W₀) exp[−(n − 1)/n] for the Weibull, where W₀ is initial body weight and n is a shape parameter. Meta-analysis of the data using mixed model and nonlinear regression procedures was conducted to identify the most appropriate growth function. Functions were compared using F-tests or Bayesian Information Criteria, which give a value based on best fit and number of parameters in the model. The three equations were fitted to five individual pig growth profiles and to the composite data. Although the Weibull had a lower residual mean square, it did not significantly improve the fit compared to the simpler models and appears to be over-parameterised. The results suggest that model selection should be based on the type and amount of data available for analysis. Residuals plot showed that Schumacher and Weibull better predict the initial growth phase, however, all models showed largest magnitude of residuals towards the end of the growth profile. The monomolecular equation was most appropriate for describing LW against cumulative feed intake and may be used to formulate diets based on the efficiency of conversion of feed to LW at various stages of the animal's life span.     

Low-frequency distortion product otoacoustic emissions in two species of kangaroo rats: implications for auditory sensitivity

Low-frequency distortion-product otoacoustic emissions were measured in two species of kangaroo rats to test the prediction that a large footdrumming species (e.g., Dipodomys spectabilis) would have greater distortion-product otoacoustic emission amplitude than a small non-footdrumming species (e.g., Dipodomys merriami), indicating better hearing sensitivity at low frequencies. Equal-level (65 dB SPL) stimulus tones (f ₁, f ₂), presented over a (f ₁) range of 200–1000 Hz, were used to evoke the 2f ₁–f ₂ distortion-product otoacoustic emission. Mean 2f ₁–f ₂ levels for D. merriami showed good correspondence to previously published audiograms for that species. Mean 2f ₁–f ₂ levels and 95% confidence intervals indicated species differences below 400 Hz, supporting the theory that low-frequency hearing sensitivity is better in large kangaroo rat species. These results suggest that the size-related divergence in footdrumming behavior may be related to differential auditory sensitivity.Abbreviations DPOAE distortion-product otoacoustic emission - OAE otoacoustic emission - PVC polyvinyl chloride     

Influence of signal filtering and sample rate on isometric torque – time parameters using a traditional isokinetic dynamometer

Isometric force- or torque-time parameters are commonly reported in the research literature. The processing methods of the electronic dynamometer-derived signal may influence the outcome measures. This study determined the influence of filtering and sample rate (SR) on isometric torque-time parameters and provides specific signal processing recommendations for future studies. Twenty-three subjects performed 49 isometric maximum voluntary contractions (MVCs) of the knee extensors on an isokinetic dynamometer. Outcome measures included peak torque (PT), and rate of torque development at peak (RTDPEAK), 50 (RTD50) and 200 (RTD200) ms for seven filter conditions including low-pass filter cutoffs at 5, 10, 20, 50, 100 and 150 Hz and a notch filter at 100 and 200 Hz. Comparisons were also made across four SR conditions at 100, 500, 1000 and 2000 Hz. The RTDPEAK variable was markedly changed (−5.4 to −37.9%) for all filter frequencies compared to the 150 Hz condition and the RTD50 variable was altered for all frequencies between 50 and 5 Hz. No differences were found for RTD200. For SR, compared to the 2000 Hz condition, differences were revealed for the 100 Hz condition for the RTDPEAK and RTD50 variables. The filtering or SR did not alter PT across any of the conditions. The filter and SR applied to the signal was capable of distorting the MVC signal and skewing the torque–time parameters, specifically for the early and maximum RTD variables of the MVC curve (RTD50 and RTDPEAK). For traditional isokinetic dynamometers, a low-pass filter cutoff of 150 Hz and a SR of at least 1000 Hz is recommended when assessing early isometric force- or torque-time MVC parameters.