Differences In Spectral Content Research Articles

Electrocorticography Analysis in Patients With Dual Neurostimulators Supports Desynchronization as a Mechanism of Action for Acute Vagal Nerve Stimulator Stimulation.

Both vagal nerve stimulation (VNS) and responsive neurostimulation (RNS System) are treatment options for medically refractory focal epilepsy. The mechanism of action of both devices remains poorly understood. Limited prior evidence suggests that acute VNS stimulation may reduce epileptiform activity and cause EEG desynchronization on electrocorticography (ECoG). Our study aims to isolate effects of VNS on ECoG as recorded by RNS System in patients who have both devices, by comparing ECoG samples with and without acute VNS stimulation. Ten 60-second ECoGs each from 22 individuals at 3 epilepsy centers were obtained-5 ECoGs with VNS "off" and 5 ECoGs with VNS "on." Electrocorticograps containing seizures or loss of telemetry connection artifact were excluded from analysis (total of 169 ECoGs were included). Electrocorticographs were analyzed for differences in spectral content by generating average spectrograms for "on" and "off" states and using a linear mixed-effects model to isolate effects of VNS stimulation. Acute VNS stimulation reduced average power in the theta band by 4.9%, beta band by 3.8%, and alpha band by 2.5%. The reduction in theta power reached statistical significance with a P value of <0.05. Our results provide evidence that acute VNS stimulation results in desynchronization of specific frequency bands (salient decrease in theta and beta bands, smaller decrease in alpha band) in ECoGs recorded by the RNS device in patients with dual (VNS and RNS) neurostimulators. This finding offers support for desynchronization as a theorized mechanism of action of VNS. Further research may lead to future improved neurostimulator efficacy by informing optimal stimulation programming parameters.

A system to mitigate deep mine tremor effects in the design of civil infrastructure

Deep mining may induce quakes reaching magnitude mL of 4.5 to 5.5 and leading to surface ground motion with Modified Mercalli intensities up to VIII. Such strong ground motions may cause serious damages in civil infrastructure in the vicinity of mines. However any adaptation of a classic seismic code in design faces an impending problem of differences in spectral content and duration between the surface records of the rockbursts and natural earthquakes, as well as in their different risk definitions. This paper presents a system to define design seismic load based on forecasted surface horizontal particle velocity from the rockbursts expected during the planned mining activities. Such forecasts are routinely prepared by the geophysical mine services. Respective seismic load may then be applied in the design of buildings and other structures to mitigate the rockburst induced seismic effects on them. For this purpose the European seismic code, Eurocode 8, is adapted.

Remote Sensing Image Matching using Sift And Affine Transformation

paper presents remote sensing image matching using sift algorithm and affine transformation. The novelty in our approach is to find the features in the reference image and then match the input image with that of reference image using Affine Transformation. Both synthetic and real data have been considered in this work for the evaluation of the proposed methodology. After registering the image, the outliers are removed. A speeded up affine invariant detector is proposed in this paper for local feature extraction. The experimental results show that the proposed algorithm decreases the redundancy of key points and speeds up the implementation. It is able to account for differences in spectral content, rotation, scale, translation, different viewpoint, and change in illumination. The proposed technique improves the computational efficiency and decrease the storage requirement.

Slowing of M1 oscillations in brain tumor patients in resting state and during movement

ObjectiveBrain tumors may severely disrupt the structure and function of the brain. While abnormal low-frequency activity can be found around tumor borders, disrupted structural connectivity may also impinge on neural activity in distant brain regions and other frequency bands. We investigated how glioma in patients with normal motor functioning affects activity in primary motor areas (M1). MethodsUsing magnetoencephalography in 12 patients with unilateral glioma located around the central sulcus, we studied activity in bilateral M1s in resting state and during movement with focus on motor-related mu (8–12Hz) and beta rhythms (15–30Hz). Principal component analysis served to test for differences in spectral content. ResultsA shift was found towards lower frequencies for M1 in the tumor hemisphere compared to M1 in the healthy hemisphere, caused by an increase in mu and decrease in beta power. This pattern was observed both in resting state and during movement. ConclusionsThis ‘slowing’ of brain oscillations in M1 resembles findings in patients with monohemispheric stroke and Parkinson’s disease. A loss of intra-cortical connectivity may account for these findings, possibly supplemented by tumor-induced changes in neurotransmitter systems. SignificanceMotor functioning may be unaffected by a spectral shift of mu and beta oscillations.

Automatic Image Registration Through Image Segmentation and SIFT

Automatic image registration (AIR) is still a present challenge for the remote sensing community. Although a wide variety of AIR methods have been proposed in the last few years, there are several drawbacks which avoid their common use in practice. The recently proposed scale invariant feature transform (SIFT) approach has already revealed to be a powerful tool for the obtention of tie points in general image processing tasks, but it has a limited performance when directly applied to remote sensing images. In this paper, a new AIR method is proposed, based on the combination of image segmentation and SIFT, complemented by a robust procedure of outlier removal. This combination allows for an accurate obtention of tie points for a pair of remote sensing images, being a powerful scheme for AIR. Both synthetic and real data have been considered in this work for the evaluation of the proposed methodology, comprising medium and high spatial resolution images, and single-band, multispectral, and hyperspectral images. A set of measures which allow for an objective evaluation of the geometric correction process quality has been used. The proposed methodology allows for a fully automatic registration of pairs of remote sensing images, leading to a subpixel accuracy for the whole considered data set. Furthermore, it is able to account for differences in spectral content, rotation, scale, translation, different viewpoint, and change in illumination.

Effect of multiple equidistant imaging: analyzing the techniques of its monochromatic reproduction and the forms of manifestation

Monochromatic imaging systems with spatial-frequency filters in the form of Fabry-Perot interferometers, concentric ring masks, and diffractive multifocal lenses are shown to realize the same effect of multiple equidistant imaging. However, the forms of manifestation of this effect are not identical due to the difference in spectral content of generated wave fields. Self-imaging fields with a discrete angular spectrum inherent in the systems with masks and interferometers are found to comprise a subclass of periodically focused fields with a continuous angular spectrum peculiar to the systems with diffractive multifocal lenses. The advantages of the latter systems are the extremely high total light efficiency and the sharply defined longitudinal localization of generated wave fields, which enhance the brightness of the reproduced images and decreases their parasitic diffraction dispersion, background noise, and blurring.

Effect of preceding speech on nonspeech sound perception

Data from Japanese quail suggest that the effect of preceding liquids (/l/ or /r/) on response to subsequent stops (/g/ or /d/) arises from general auditory processes sensitive to the spectral structure of sound [A. J. Lotto, K. R. Kluender, and L. L. Holt, J. Acoust. Soc. Am. 102, 1134–1140 (1997)]. If spectral content is key, appropriate nonspeech sounds should influence perception of speech sounds and vice versa. The former effect has been demonstrated [A. J. Lotto and K. R. Kluender, Percept. Psychophys. 60, 602–619 (1998)]. The current experiment investigated the influence of speech on the perception of nonspeech sounds. Nonspeech stimuli were 80-ms chirps modeled after the F2 and F3 transitions in /ga/ and /da/. F3 onset was increased in equal steps from 1800 Hz (/ga/ analog) to 2700 Hz (/da/ analog) to create a ten-member series. During AX discrimination trials, listeners heard chirps that were three steps apart on the series. Each chirp was preceded by a synthesized /al/ or /ar/. Results showed context effects predicted from differences in spectral content between the syllables and chirps. These results are consistent with the hypothesis that spectral contrast influences context effects in speech perception. [Work supported by ONR, NOHR, and CNBC.]

Parameter optimization of influence functions in mining subsidence

Deep mining may induce quakes reaching magnitude mL of 4.5 to 5.5 and leading to surface ground motion with Modified Mercalli intensities up to VIII. Such strong ground motions may cause serious damages in civil infrastructure in the vicinity of mines. However any adaptation of a classic seismic code in design faces an impending problem of differences in spectral content and duration between the surface records of the rockbursts and natural earthquakes, as well as in their different risk definitions. This paper presents a system to define design seismic load based on forecasted surface horizontal particle velocity from the rockbursts expected during the planned mining activities. Such forecasts are routinely prepared by the geophysical mine services. Respective seismic load may then be applied in the design of buildings and other structures to mitigate the rockburst induced seismic effects on them. For this purpose the European seismic code, Eurocode 8, is adapted.

Spectro-temporal factors in the perceptual segregation of tonal sequences

Spectral factors such as differences in harmonic content are powerful cues in the organization of tonal sequences. Temporal factors such as rise time, however, have been shown to be poor cues [W. M. Hartmann and D. Johnson, Mus. Perc. 9(2), 155–184 (1991)]. The relative salience of these factors was investigated further using complex tones sequenced in a repeating ABA-‘‘gallop’’ format, under conditions in which tones A and B had the same, or different harmonic content and/or temporal envelope shape. The F0 difference between A and B was initially 0 Hz, but increased over the course of a trial, until terminated by a listener, indicating perceptual segregation of the input sequence into sub-sequences comprising A and B tones, respectively. The F0 difference required to reach this segregation threshold provided a measure of the efficacy of stimulus features of A and B as cues for sequential organization. Sequences combining differences in spectral content and temporal envelope shape required the smallest F0 change for segregation. Sequences of tones with the same harmonic structure and temporal envelope required the largest F0 changes, while the other conditions fell in the middle of this range. Results will be discussed in terms of implications for sequential organization as well as for the perception of timbre. [Work supported by NSERC, Canada.]

Spectral content as a cue to perceived auditory distance.

Changes in the spectral content of wide-band auditory stimuli have been repeatedly implicated as a possible cue to the distance of a sound source. Few of the previous studies of this factor, however, have considered whether the cue provided by spectral content serves as an absolute or a relative cue. That is, can differences in spectral content indicate systematic differences in distance even on their first presentation to a listener, or must the listener be able to compare sounds with one another in order to perceive some change in their distances? An attempt to answer this question and simultaneously to evaluate the possibly confounding influence of changes in the sound level and/or the loudness of the stimuli are described in this paper. The results indicate that a decrease in high-frequency content (as might physically be produced by passage through a greater amount of air) can lead to increases in perceived auditory distance, but only when compared with similar sounds having a somewhat different high-frequency content, ie spectral information can serve as a relative cue for auditory distance, independent of changes in overall sound level.

Sensitometric responses of selected medical radiographic films.

Radiographic films produce different densities and contrast when processor changes occur, and the magnitude and rate of change vary with film type. The ability to detect and interpret the clinical importance of film density changes may depend on the method of sensitometry used. The characteristics of several medical radiographic films and various sensitometers were examined under three sensitometric variations and five processing variations. Of all variations used, only exposure with a single-versus a double-sided sensitometer caused a film type to have a marked different response. The results indicate that mismatching the sensitometer spectral output with the spectral sensitivity of the film in most cases does not affect the density changes of the film. The fact that a few films may be sensitive to differences in spectral content of the exposing light and dual- versus single-sided exposure and that only a limited number of film types were tested, however, leads to the prudent conclusion that the exposure conditions for quality control purposes should match clinical exposure conditions as closely as possible.

Auditory Brain Stem Response Spectral Content in Comatose Head-Injured Patients

Auditory brain stem response (ABR) spectral content was analyzed for 25 normal subjects and 70 comatose, severely head-injured subjects. The normal ABR spectrum was characterized by energy peaks in three main regions: 0 to 200 Hz, 500 to 600 Hz and 900 to 1000 Hz. Head-injured subjects, in contrast, showed less overall ABR spectral energy. Even head-injured subjects with normal ABR interwave latency values had reduced spectral energy in comparison to the normal group. Among these subjects, there were differences in spectral content for subjects with good neurologic outcome versus those who died within 2 weeks post injury. Finally, head-injured subjects with abnormal interwave latency intervals typically showed distinctive spectral patterns. This subject group demonstrated energy peaks in frequency regions which, for the other groups, were void of energy peaks. Rationale for further study of ABR spectral content is offered.

The effect of electrode position on atrial sensing for physiologically responsive cardiac pacemakers

Fully automatic pacing systems rely on accurate identification of spontaneous atrial signals for physiologically responsive pacing. These signals must be discriminated from far-field ventricular activity, which might otherwise be sensed in the atrium. To amplify on the previously reported superiority of bipolar signals and high-impedance circuitry for atrial sensing, we studied the effects of various intraatrial electrode positions on the atrial and ventricular contribution to electrograms recorded in this chamber. Compared with other intraatrial endocardial sites, right atrial signals were greatest in amplitude and slew rate in the appendage (RAA), averaging 3.3 ± 0.41 mV and 1.15 ± 0.16 V/sec (mean ± SEM), respectively. These values were substantially higher than in the low atrium ( p < 0.001 and 0.0005 for amplitude and slew rate, respectively) and the high lateral atrium ( p < 0.05 for slew rate). Appendage atrial electrograms also had significantly higher amplitude and slew rate than far-field R waves recorded here ( p < 0.0001 for both). Additionally, the greatest difference in spectral content between atrial and far-field ventricular signals was also observed in the RAA. Thus, parameters in the domain of both time and frequency identified the RAA as the superior location for atrial sensing. Except for phrenic nerve problems with pacing, the HRA also appears to be a suitable electrode location for sensing. These considerations are germane in light of a growing number of atrial active and passive fixation leads now being employed for physiologic pacing.

SIMS micro-analysis with a gallium ion microprobe

SIMS microanalysis is readily achieved by the adoption of the liquid metal field ion source for formation of the primary ion probe. These sources exhibit high brightness and small source size and permit the formation of high intensity sub-micron ion beams at low energies (⩽10 KeV). Operation is simple, UHV compatible and well suited to mulit-technique surface analysis systems, as well as dedicated SIMS instrumentation. Beam characteristics for a gallium probe allow image resolutions down to 1000 Å with probe currents ranging from 50 pA at high resolution, to maximum currents in excess of 100 nA. Image recording times range from 10 s to 10 min, typically. A gallium source has been in routine operation for over one year on a quadrupole based SIMS instrument, and a wide range of experience gained on various specimens. These include metals, semiconductors, insulators, polymers and biological materials. Some comparisons have been made between the use of argona and gallium beams with respect to spectral content and elemental sensitivities. In general the sensitivities are similar, while the main difference in spectral content is the presence of secondary ions of gallium and gallium complexes. Insulating specimens which have proved very difficult in Auger analysis such as optical fibres, or powders, have been studied more readily with the gallium probe in SIMS analysis. In this case charge neutralization is effected with an accurately positioned 500 eV electron beam.

ORIENTATION AND LEVER RESPONDING IN AUDITORY DISCRIMINATIONS IN SQUIRREL MONKEYS1

Head orientation during auditory discriminations was studies in squirrel monkeys using a two-lever trial-by-trial procedure. Animals were studied using auditory discriminations based on the position of the sound and on the spectral content differences between a pure tone and a noise. After the percentage of correct responses reached asymptote, head orientation was measured using videotape recordings. Orientation occurred on virtually every trial and was under the control of the position of the sound under all conditions. Lever responding was controlled by the same parameters of the sound under some conditions, and by different parameters in others. Orientation and lever responding were correlated (a level response could be predicted from the direction of orientation) when both responses were under the control of the same parameters of the sound. The two responses were uncorrelated when they were controlled by different parameters of the sound. Orientation and lever responding were not functionally related.

P-wave Spectra from Underground Nuclear Explosions

This paper reports observations of P-wave spectra from underground nuclear explosions for periods greater than about 1 s. The spectra have a maximum at about 2–3 s and decrease rapidly at longer periods. Two phenomena could cause such a decrease: (1) The surface reflection (pP), with its polarity opposite to that of the direct P wave, might differentiate the long-period signal and cause a modulation of 2|sin ωt0/2| where t0 is the interval of time between P and pP; or (2) the source time function for the pressure on the boundary of the elastic zone surrounding the explosion might more nearly resemble an impulse than a step function as often assumed. The data are consistent with the simultaneous occurrence of both phenomena, but they are of insufficient quality or quantity to establish which is more important. If other information shows that the reflection does not have a large effect on the observed spectrum, then the data show that the source time function is primarily an impulse. In addition, the pronounced difference in spectral content of P waves from earthquakes and underground nuclear explosions suggests a method for identification that is applicable for explosions large enough to be recorded by long-period seismographs at teleseismic distances. This method may be particularly important when long-period instruments are disturbed by other events and methods of identification that rely on analysis of surface waves become inapplicable.