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PubMed1999

Missing-data model of vowel identification.

Vowel identity correlates well with the shape of the transfer function of the vocal tract, in particular the position of the first two or three formant peaks. However, in voiced speech the transfer function is sampled at multiples of the fundamental frequency (F0), and the short-term spectrum contains peaks at those frequencies, rather than at formants. It is not clear how the auditory system estimates the original spectral envelope from the vowel waveform. Cochlear excitation patterns, for example, resolve harmonics in the low-frequency region and their shape varies strongly with F0. The problem cannot be cured by smoothing: lag-domain components of the spectral envelope are aliased and cause F0-dependent distortion. The problem is severe at high F0's where the spectral envelope is severely undersampled. This paper treats vowel identification as a process of pattern recognition with missing data. Matching is restricted to available data, and missing data are ignored using an F0-dependent weighting function that emphasizes regions near harmonics. The model is presented in two versions: a frequency-domain version based on short-term spectra, or tonotopic excitation patterns, and a time-domain version based on autocorrelation functions. It accounts for the relative F0-independency observed in vowel identification.

Humans↗
PubMed1998

High prevalence of arrhythmias in elderly male athletes with a lifelong history of regular strenuous exercise.

OBJECTIVE: To characterise cardiac arrhythmias and cardiac autonomic function in 11 elderly men (mean (SD) age 73.2 (2.8) years) with a lifelong history of regular very strenuous, exercise. A control group of 12 healthy sedentary or moderately physically active men (74.5 (2.7) years) was also studied. DESIGN: 48 hour ambulatory electrocardiograms were recorded. Cardiac autonomic function was estimated from power spectral analysis of heart rate variability. Maximal oxygen uptake during treadmill exercise testing was 2.91 (0.52) l (41 (7) ml/kg). RESULTS: Nine of 11 athletes had complex ventricular arrhythmias compared with five of 12 controls. Seven athletes but none of the controls had episodes of heart rate below 40 beats/min and two athletes had RR intervals longer than two seconds. Heart rate variability in the athletes was higher than in the controls. CONCLUSIONS: Elderly athletes with a lifelong training history seem to have more complex arrhythmias and profound bradyarrhythmias than do healthy elderly controls, which may increase the risk of sudden cardiac death. In contrast, the age related decrease in heart rate variability seems to be retarded, which has a positive prognostic value and may decrease the risk of life threatening ventricular arrhythmias.

Aged↗
PubMed2006

Are sparse-coding simple cell receptive field models physiologically plausible?

Olshausen and Field (1996) developed a simple cell receptive field model for natural scene processing in V1, based on unsupervised learning and non-orthogonal basis function optimization of an overcomplete representation of visual space. The model was originally tested with an ensemble of whitened natural scenes, simulating pre-cortical filtering in the retinal ganglia and lateral geniculate nucleus, and the basis functions qualitatively resembled the orientation-specific responses of V1 simple cells in the spatial domain. In this study, the quantitative tuning responses of the basis functions in the spectral domain are estimated using a Gaussian model, to determine their goodness-of-fit to the known bandwidths of simple cells in primate V1. Five simulation experiments which examined key features of the model are reported: changing the size of the basis functions; using a complete versus over-complete representation; changing the sparseness factor; using a variable learning rate; and mapping the basis functions with a whitening spatial function. The key finding of this study is that across all image themes, basis function sizes, number of basis functions, sparseness factors and learning rates, the spatial-frequency tuning did not closely resemble that of primate area 17 -- the model results more closely resembled the unclassified cat neurones of area 19 with a single exception, and not area 17 as predicted.

Action Potentials↗
PubMed1987

Influence of norepinephrine and angiotensin II on vasomotion of renal blood supply in humans.

Oscillatory behavior of smooth muscle, including arterial smooth muscle, has been identified in many preparations. In this study we have extended observations on vasomotion of the renal blood supply in humans by assessing the response to norepinephrine or angiotensin II infused directly into the renal artery in doses sufficient to reduce renal blood flow by 25-33% but not influence blood pressure. In placebo-treated patients, renal blood flow and the indexes of vasomotion determined by an estimation of power spectral density of xenon transit through the human kidney did not change. Norepinephrine induced a striking increase in the amplitude but not the cycle length of oscillatory activity, whereas angiotensin (despite a somewhat larger reduction in renal blood flow) induced only a modest change in amplitude. The phasic response to norepinephrine infused continuously makes it unnecessary to invoke phasic norepinephrine release in the response to maneuvers that increase sympathetic nervous system activity. Moreover, oscillatory activity reflects phenomena that may be related to but are not dependent on changes in mean renal blood flow. The results of this study may provide insight into the pathogenesis of the increase in vasomotion evident in the renal blood supply of some patients with essential hypertension.

Angiotensin II↗
PubMed1989

Renal vasomotion in essential hypertension: influence of vasodilators.

To assess factors responsible for phasic behavior of renal blood flow in essential hypertension, we applied an analytic method based on the estimation of power spectral density to xenon transit through the kidney and examined the renal vasodilator response to a range of agents in 53 normal subjects and 53 patients with essential hypertension. The renal vasodilator response to the calcium channel blocking agent diltiazem, but not the response to alpha-adrenergic blockade (phentolamine) or angiotensin converting enzyme inhibition (teprotide or captopril), was associated with a significant reduction in the amplitude of renal vasomotion. Acetylcholine, a vasodilator that acts through the release of a vasorelaxant factor or factors from endothelium, induced an unanticipated increase in renal vasomotion. These observations further dissociate factors responsible for basal renal vascular tone and periodic changes in renal vascular tone and raise the possibility that abnormalities in the flux of calcium into renal arterioles contribute to increased renal vasomotion in essential hypertension.

Angiotensin II↗
PubMedDate not supplied

Vasomotion of renal blood flow in essential hypertension. Oscillations in xenon transit.

To assess the frequency and magnitude of phasic renal blood flow changes in essential hypertension, we applied an analytical method based on the estimation of power spectral density to xenon transit through the kidney. Despite similar age and gender distribution of the patients and exclusion of those with accelerated hypertension, mean renal blood flow was significantly lower in 100 patients with essential hypertension (299 +/- 8 ml/100 g/min) than in the 144 normal subjects (335 +/- 6 ml/100 g/min; p less than 0.001). Normalized power, the index of oscillatory behavior, was more than twice normal in patients with essential hypertension (p less than 0.001), but there was no difference in the frequency or cycle length of the oscillation. Two maneuvers that induced renal vasoconstriction, the application of cuffs to the thighs which were then inflated to diastolic blood pressure and an emotional provocation, reduced renal blood flow much more in patients with essential hypertension (p less than 0.01) in association with a striking increase in normalized power (p less than 0.001). The oscillations, which reflected not the phasic blood pressure change but rather the phasic change in renal perfusion, provided additional evidence that renal vasoconstriction plays an active role in the pathogenesis of essential hypertension.

Blood Pressure↗
PubMed2003

Fine structure of the low-frequency spectra of heart rate and blood pressure.

BACKGROUND: The aim of this study was to explore the principal frequency components of the heart rate and blood pressure variability in the low frequency (LF) and very low frequency (VLF) band. The spectral composition of the R-R interval (RRI) and systolic arterial blood pressure (SAP) in the frequency range below 0.15 Hz were carefully analyzed using three different spectral methods: Fast Fourier transform (FFT), Wigner-Ville distribution (WVD), and autoregression (AR). All spectral methods were used to create time-frequency plots to uncover the principal spectral components that are least dependent on time. The accurate frequencies of these components were calculated from the pole decomposition of the AR spectral density after determining the optimal model order--the most crucial factor when using this method--with the help of FFT and WVD methods. RESULTS: Spectral analysis of the RRI and SAP of 12 healthy subjects revealed that there are always at least three spectral components below 0.15 Hz. The three principal frequency components are 0.026 +/- 0.003 (mean +/- SD) Hz, 0.076 +/- 0.012 Hz, and 0.117 +/- 0.016 Hz. These principal components vary only slightly over time. FFT-based coherence and phase-function analysis suggests that the second and third components are related to the baroreflex control of blood pressure, since the phase difference between SAP and RRI was negative and almost constant, whereas the origin of the first component is different since no clear SAP-RRI phase relationship was found. CONCLUSION: The above data indicate that spontaneous fluctuations in heart rate and blood pressure within the standard low-frequency range of 0.04-0.15 Hz typically occur at two frequency components rather than only at one as widely believed, and these components are not harmonically related. This new observation in humans can help explain divergent results in the literature concerning spontaneous low-frequency oscillations. It also raises methodological and computational questions regarding the usability and validity of the low-frequency spectral band when estimating sympathetic activity and baroreflex gain.

Adult↗
PubMed2006

Interpretation of the surface electromyogram in dynamic contractions.

This review focuses on methods for extracting information from the surface EMG recorded in dynamic contractions. It examines the techniques, requirements, and limitations associated with detecting the timing of muscle activation, assessing the modulation of signal amplitude, performing EMG spectral analysis, and estimating conduction velocity. The conclusion is that interpretation of the surface EMG in dynamic tasks requires caution.

Denmark↗
PubMed2004

Effects of nonpeptide and selective V1 and V2 antagonists on blood pressure short-term variability in spontaneously hypertensive rats.

Effects of V(1) (OPC-21268) and V(2) (OPC-31260) vasopressin antagonists on blood pressure (BP) short-term variability were investigated in adult spontaneously hypertensive rats (SHR) under basal conditions and after the stimulation of vasopressin release by hemorrhage. BP was recorded intra-arterially and sampled at 20 Hz to be analyzed on a personal computer. BP time spectra were calculated on 30 stationary overlapping 2048 point-time series. Spectral power was estimated in total (0.00976 - 3 Hz), very low frequency (VLF: 0.00976 - 0.195 Hz), low frequency (LF: 0.195 - 0.605 Hz), and high frequency (HF: 0.8 - 3 Hz) regions. Under basal conditions a V(1) antagonist (5 mg/kg, i.v.) decreased BP without affecting BP variability, while combined (V(1) + V(2)) blockade or V(2) blockade (1 mg/kg, i.v.) alone did not affect cardiovascular parameters. Mild hemorrhage (5 ml/kg per min) increased HF-BP variability, while moderate (10 ml/kg per min) and massive (15 ml/kg per min) hemorrhage did not affect it. In V(1), but not V(2), antagonist pre-treated SHR HF-BP increased significantly after moderate and massive hemorrhage. V(1) or V(2) antagonist pre-treatment also enhanced VLF-BP variability during massive hemorrhage. Moreover V(1) blockade prevented hemorrhage-induced bradycardia, while V(2) blockade potentiated it. It follows that in adult SHR, vasopressin buffers BP oscillations in HF and VLF frequency domains only in hypovolaemic conditions and that the modulation of the autonomic adjustment of the HR to hemorrhage by vasopressin is preserved.

Animals↗
PubMed2002

Photonic encoder and decoder for optical code-division multiplexing with time-to-space converters and angle-multiplexed holograms.

A photonic encoder-decoder pair for optical code-division multiplexing (OCDM) that uses time-to-space converters and angle-multiplexed holograms is proposed. The encoder converts the pulse from each input port into a specific code and multiplexes input signals into the output port. The hologram in the decoder generates a correlation waveform between the transmitted code and the recorded code. The performance of the OCDM system with the encoder-decoder pair is estimated. The maximum spectral efficiency for 8-bit length orthogonal codes in the worst case at a bit-error rate of 10(-9) is 0.17 (bits/s)/Hz when the number of channels is 8.

Journal Article↗
PubMed2003

Spatial spectrum analysis of wave-front correction with a segmented mirror.

An expression is derived for the spatial power spectrum of wave-front errors after correction with a segmented mirror. This includes estimates of the spectral contributions of segment piston and tilt corrections and spatial aliasing by a regular array of segments. The approach allows rapid computation of wave-front error spectra in systems with highly segmented mirrors.

Journal Article↗
PubMed1997

Bayesian color constancy.

The problem of color constancy may be solved if we can recover the physical properties of illuminants and surfaces from photosensor responses. We consider this problem within the framework of Bayesian decision theory. First, we model the relation among illuminants, surfaces, and photosensor responses. Second, we construct prior distributions that describe the probability that particular illuminants and surfaces exist in the world. Given a set of photosensor responses, we can then use Bayes's rule to compute the posterior distribution for the illuminants and the surfaces in the scene. There are two widely used methods for obtaining a single best estimate from a posterior distribution. These are maximum a posteriori (MAP) and minimum mean-square-error (MMSE) estimation. We argue that neither is appropriate for perception problems. We describe a new estimator, which we call the maximum local mass (MLM) estimate, that integrates local probability density. The new method uses an optimality criterion that is appropriate for perception tasks: It finds the most probable approximately correct answer. For the case of low observation noise, we provide an efficient approximation. We develop the MLM estimator for the color-constancy problem in which flat matte surfaces are uniformly illuminated. In simulations we show that the MLM method performs better than the MAP estimator and better than a number of standard color-constancy algorithms. We note conditions under which even the optimal estimator produces poor estimates: when the spectral properties of the surfaces in the scene are biased.

Color Perception↗
PubMed2006

Highly sensitive visible-blind extreme ultraviolet Ni/4H-SiC Schottky photodiodes with large detection area.

Ni/4H-SiC Schottky photodiodes of 5 mm x 5 mm area have been fabricated and characterized. The photodiodes show less than 0.1 pA dark current at -4 V and an ideality factor of 1.06. A quantum efficiency (QE) between 3 and 400 nm has been calibrated and compared with Si photodiodes optimized for extreme ultraviolet (EUV) detection. In the EUV region, the QE of SiC detectors increases from 0.14 electrons/photon at 120 nm to 30 electrons/photon at 3 nm. The mean energy of electron-hole pair generation of 4H-SiC estimated from the spectral QE is found to be 7.9 eV.

Journal Article↗
PubMed2006

Probabilistic encoding of vocalizations in macaque ventral lateral prefrontal cortex.

We examined strategies for classifying macaque vocalizations into their corresponding categories, as well as whether or not there was evidence that prefrontal auditory neurons were related to this process. We found that static estimates of the spectral and temporal contrasts of the calls were not effective features for discriminating among the call classes. A hidden Markov model (HMM), however, was more effective at discriminating among the call classes, reaching a performance of almost 75% correct. Finally, we found that the responses of prefrontal auditory neurons could be predicted more effectively as linear functions of the probabilistic output of the HMM than as linear functions of the spectral features of the calls. This provides evidence that, for call recognition, the macaque auditory system likely performs dynamic processing of vocalizations, and that prefrontal auditory neurons carry a signal related to the output of this processing.

Acoustic Stimulation↗
PubMed2004

Interactive effects of task difficulty and personality on mood and heart rate variability.

Susceptibility to stress would presumably be different from person to person and be affected by the cause of the given stress. The purpose of this study was to investigate the interactive effects of task difficulty and subject's personality on mood and autonomic nervous function when stress was induced experimentally by tasks involving 3 degrees of difficulty: easy (Task A), difficult but controllable (Task B), and very difficult and uncontrollable (Task C). Twelve healthy female subjects volunteered for the experiment. We assessed their personalities using the Minnesota Multiphasic Personality Inventory (MMPI) questionnaire. Mood states were evaluated by a profile of mood states and a frontal alpha laterality ratio (FALR). Autonomic nervous function was estimated by a spectral analysis of heart rate variability (HRV). Repeated measures analysis of variance applied to two groups (low- and high-) divided by a median split of MMPI clinical scales, revealed significant interactions of time course x task difficulty x Hs (hypochondriasis) in FALR and time course x task difficulty x Pt (psychasthenia) in a low-frequency component and in a high-frequency component of HRV, and in FALR. The differences between low- and high-Hs, and low- and high-Pt were more obvious in Task B session. High-Hs group, whose members tend to place overemphasis on existing physical disorders, showed more negative FALR throughout the session, which would indicate prolonged negative mood possibly due to the task. High-Pt group, whose members tend to be susceptible to stress, showed sympathetic predominance during task period and parasympathetic predominance after task period, which would imply a tendency to overreact. These results suggest that task difficulties would affect mood states assessed by FALR and/or autonomic nervous function differently depending on the subject's personality, especially on Hs and Pt.

Adult↗
PubMedDate not supplied

[Influence of heart failure severity on heart rate variability].

INTRODUCTION: Autonomic regulation of cardiovascular functions in congestive heart failure is characterised by enhanced sympathetic and diminished parasympathetic activity. The long term predominance of sympathetic tone is a significant factor in arrhythmogenesis, sudden cardiac death, and progressive pump failure. Heart rate variability (HRV) is a noninvasive method for estimating the sympatho vagal balance in cardiovascular control. AIM: The aim of this study was to analyse the influence of heart failure severity on HRV. METHOD: HRV was estimated through the spectral analysis of short term ECG (Cardiovit AT 60, Schiller, CH) in 63 patients (78% male, mean age 56.9 +/- 10.9 years) and 14 healthy volunteers (57.1% male, mean age 53.1 +/- 8.2 years). The following spectral components were measured: VLF (very low frequency), LF (low frequency), HF (high frequency), and total power (Tot Power). RESULTS: All spectral componentswere statistically, significantly lower in patients with heart failure in comparison to healthy controls (VLF: 159.89 +/- 147.02 vs. 285.50 +/- 202.77 ms2; p = 0.023, LF: 161.48 +/- 204.01 vs. 474.57 +/- 362.93 ms2; p < 0.001, HF: 88.58 +/- 102.47 vs. 362.71+/- 318.28 ms2; p < 0.001), as well as total power (Tot Power: 723.39 +/- 644.52 vs. 1807.29 +/- 1204.74 ms2; p < 0.001). A significant, negative correlation between HRV parameters and NYHA class was detected in heart failure patients (VLF: r = -0.391; p = 0.002, LF: r = -0.401; p = 0.001, and Tot Power r = -0.372; p = 0.003). Ejection fraction proved to be in significant, positive correlation to VLF (r = 0.541; p = 0.002), LF (r = 0.531; p = 0.003), HF (r = 0.418; p = 0.020), and Tot Power (r = 0.457; p = 0.013). CONCLUSION: Significant HRV reduction is a precursor to incipient heart failure (NYHA I). In heart failure progression, total power as well as the power of all spectral components is progressively reduced. LF and Tot Power are the most prominent parameters for discriminating between the different stages of heart failure. These results could promote HRV as an important decision-making tool in heart failure treatment as well as in monitoring the results of that treatment.

Disease Progression↗
PubMed2006

Endothelial glycocalyx damage coincides with microalbuminuria in type 1 diabetes.

Chronic hyperglycemia underlies microvascular complications in patients with type 1 diabetes. The mechanisms leading to these vascular complications are not fully understood. Recently, we observed that acute hyperglycemia results in endothelial glycocalyx damage. To establish whether glycocalyx is associated with microvascular damage, we performed glycocalyx perturbation volume measurements in type 1 diabetic patients with microalbuminuria (DM1-MA group; n = 7), without microalbuminuria (DM1-NA group; n = 7), and in age-matched control subjects (CON; n = 7). Systemic glycocalyx volume was determined comparing intravascular distribution volume of a glycocalyx-permeable tracer (dextran 40) to that of a glycocalyx-impermeable tracer (labeled erythrocytes). Sublingual capillaries were visualized using orthogonal polarization spectral microscopy to estimate microvascular glycocalyx. Patients and control subjects were matched according to age and BMI. Glycocalyx volume decreased in a stepwise fashion from CON, DM1-NA, and finally DM1-MA subjects (1.5 +/- 0.1, 0.8 +/- 0.4, and 0.2 +/- 0.1 l, respectively, P < 0.05). Microvascular glycocalyx in sublingual capillaries was also decreased in type 1 diabetes versus the control group (0.5 +/- 0.1 vs. 0.9 +/- 0.1 microm, P < 0.05). Plasma hyaluronan, a principal glycocalyx constituent, and hyaluronidase were increased in type 1 diabetes. In conclusion, type 1 diabetic patients are characterized by endothelial glycocalyx damage, the severity of which is increased in presence of microalbuminuria.

Adult↗
PubMed1984

Interindividual differences in a set of biological rhythms documented during the high arctic summer (79 degrees N) in three healthy subjects.

The High Arctic summer with its permanent sunlight provides a situation in which one of the natural synchronizers, the light-dark alternation, is minimal. During the summers of 1981 and 1982 three healthy right-handed geographers who were performing field studies in Svalbard as part of their own research volunteered to document, 4-6 times per 24 hr for respectively 63, 141 and 147 days, a set of circadian rhythms: self-rated fatigue, oral temperature, grip strength of both hands, heart rate and times of awakening and retiring. Tests were performed before departure from France, in Svalbard (79 degrees N latitude) where their daily activities were often strenuous, and after returning to France. Time series were treated individually according to three methods: display of data as a function of time, cosinor analyses to quantify rhythm parameters, and spectral analyses to estimate component periods of rhythms. Circadian parameters such as period and acrophase of activity-rest, oral temperature and fatigue rhythms were not altered. On the other hand, the circadian rhythm in grip strength was altered: the period differed from 24 hr in one subject, while grip strength acrophase of the left, but not the right, hand of the other two subjects was phase shifted during the sojourn in Svalbard. A prominent circahemidian (about 12 hr) rhythm was observed in two subjects for their heart rate in Svalbard, while a prominent circadian rhythm (differing from exactly 24 hr) was observed in France associated with a small circahemidian component.

Activity Cycles↗