Fusion Threshold Research Articles

The Relationship Between Concurrent Speech Segregation, Pitch-Based Streaming of Vowel Sequences, and Frequency Selectivity

Simultaneous and sequential segregation form the basis of auditory scene analysis and are likely involved in concurrent speech segregation. However, previous work showed that speech-in-noise perception was uncorrelated with simultaneous segregation, whereas it appeared to be related to the pure-tone fusion threshold of sequential streaming. The current study aimed to clarify the relationships between pitch-based speech-in-speech segregation, pitch-based streaming, and frequency selectivity. Twenty-three listeners with close to normal hearing were involved. Speech-in-speech perception was measured using words presented in a time-reversed single talker background, with various pitch differences between target and masker. Streaming performance was measured using an objective order-naming task on vowel sequences. Auditory filter widths were derived using a notch-noise method. Results showed a correlation between the effect of pitch on speech-in-speech perception and the effect of pitch on streaming performance. However, frequency selectivity was found to correlate with average speech-in-speech perception but not with streaming, and only in the region of the second formant. These latter results are consistent with the hypothesis that pitch-based streaming probably relies on pitch discrimination, which is only poorly correlated to frequency selectivity. Further, these results suggest that mild impairments in frequency selectivity do not systematically impair pitch-based streaming.

Time-dependent Hartree-Fock studies of the dynamical fusion threshold

A microscopic description of dynamical fusion threshold in heavy ion collisions is performed in the framework of time-dependent Hartree-Fock (TDHF) theory using Skyrme energy density functional (EDF). TDHF fusion threshold is in a better agreement with experimental fusion barrier. We find that the onset of extra push lies at the effective fissility 33, which is consistent with the prediction of Swiatecki’s macroscopic model. The extra push energy in our TDHF simulation is systematically smaller than the prediction in macroscopic model. The important dynamical effects and the way to fit the parameter might be responsible for the different results.

The placebo effect on psychomotor performance and working memory capacity: randomized single blind cross-over trial.

Imaging studies show that placebo enhance release of dopamine in the mesolimbic and mesocortical tracts. Dopamine in these areas are involved in attention and working memory function. We wanted to investigating the effect of placebo on psychomotor function and working memory capacity. 31 medical students participated in this single blind, crossover trial. Choice reaction time, critical flicker fusion threshold, n-back working memory tasks measured before and after one hour of the students receiving placebo in three different occasions as stimulant, unknown, and inert substance. Placebo, as stimulant, significantly enhanced choice reaction time and working memory function (P < 0.05) while showed no significant effect on critical flicker fusion threshold (P > 0.05). Placebo as unknown significantly deteriorates working memory capacity (P < 0.05). Placebo as inert substance shows no significant changes regarding choice reaction time, critical flicker fusion threshold, and working memory task. Placebo, as stimulant enhanced attention and improved working memory capacity, while as unknown may deteriorate working memory function.

Adaptive ROC-based ensembles of HMMs applied to anomaly detection

Hidden Markov models (HMMs) have been successfully applied in many intrusion detection applications, including anomaly detection from sequences of operating system calls. In practice, anomaly detection systems (ADSs) based on HMMs typically generate false alarms because they are designed using limited amount of representative training data. Since new data may become available over time, an important feature of an ADS is the ability to accommodate newly acquired data incrementally, after it has originally been trained and deployed for operations. In this paper, a system based on the receiver operating characteristic (ROC) is proposed to efficiently adapt ensembles of HMMs (EoHMMs) in response to new data, according to a learn-and-combine approach. When a new block of training data becomes available, a pool of base HMMs is generated from the data using a different number of HMM states and random initializations. The responses from the newly trained HMMs are then combined to those of the previously trained HMMs in ROC space using a novel incremental Boolean combination (incrBC) technique. Finally, specialized algorithms for model management allow to select a diversified EoHMM from the pool, and adapt Boolean fusion functions and thresholds for improved performance, while it prunes redundant base HMMs. The proposed system is capable of changing the desired operating point during operations, and this point can be adjusted to changes in prior probabilities and costs of errors. Computer simulations conducted on synthetic and real-world host-based intrusion detection data indicate that the proposed system can achieve a significantly higher level of performance than when parameters of a single best HMM are estimated, at each learning stage, using reference batch and incremental learning techniques. It also outperforms the learn-and-combine approaches using static fusion functions (e.g., majority voting). Over time, the proposed ensemble selection algorithms form compact EoHMMs, while maintaining or improving system accuracy. Pruning allows to limit the pool size from increasing indefinitely, thereby reducing the storage space for accommodating HMMs parameters without negatively affecting the overall EoHMM performance. Although applied for HMM-based ADSs, the proposed approach is general and can be employed for a wide range of classifiers and detection applications.

Fatiga del sistema nervioso después de realizar un test de capacidad de sprints repetidos (RSA) en jugadores de fútbol de categoría juvenil

Introduction and objectives Several authors have studied the influence of exercise on the nervous system and cognitive performance in untrained subjects and different stimuli such as intense anaerobic exercise to exhaustion, and submaximal endurance exercises using the Flicker Fusion Threshold (UFF). The effect on the central nervous system stimulation in repeated sprints testing has not been studied. The aims of this work are study the changes in Flicker Fusion thresholds before and after a test of repeated sprints (RSA) in soccer players, to evaluate the fatigue of the central nervous system. Methods We analysed 21 soccer players (18.1 ± 1.0 years, 72.1 ± 12.4 kg and 175.3 ± 6.2 cm). Each player completed the RSA test (7 × 30 m sprints with 20 seconds rest between each sprint). We analysed UFF, ascending (UFFa), descending (UFFd) and classical (UFFc), the subjective criterion (CS) and sensory sensitivity (SS), before and after the RSA test. Each subject performed the UFF test three times and an average value obtained. Results The results show how the values increased after the test: CS 77.8%, SS 2.6%, UFFc 77.8%, UFFd 1.3% and UFFa 4.0%, although none significantly ( P < .05). Conclusions With these results we conclude that the RSA does not generate fatigue in the central nervous system measured by Flicker Fusion Threshold.

The relation between the macular carotenoids, lutein and zeaxanthin, and temporal vision

Lutein (L) and zeaxanthin (Z) are the dominant carotenoids within the central retina (there, termed macular pigment, MP) and brain (approximately 70% of total carotenoid concentration). Past studies have shown that MP is related to many static indicators of visual performance, such as visibility and disability glare. It has also been shown that MP is related to a dynamic measure of visual performance, the critical flicker fusion threshold (CFF). In this study, we examine whether MP is related to CFF in a larger sample. We also test the relation between MP and the more complete temporal contrast sensitivity function (TCSF). A total of 70 participants were assessed for a comparison of MP and the full temporal function. A separate pool of 354 participants was assessed for a MP and CFF comparison. Peak MP density was measured psychophysically (via heterochromatic flicker photometry) using a 1-degree diameter test. CFF was measured using a 1-degree 570 nm test varied at 100% modulation. The full TCSF was measured centrally using a 1-degree, 660 nm test (the modulation depth of which could be adjusted directly by the subject) centered within a 5.5-degree, 660 nm surround. A small fixation point was used to test a 7-degree parafoveal site. MP density was positively related to temporal function as assessed by the full TCSF in the center (n = 70, r = -0.29, p < 0.01) but not at the parafoveal location (p < 0.07). MP was also positively related to critical flicker fusion thresholds (n = 354, r = 0.21, p < 0.0001).

Temporal Integration in Visual Word Recognition

When two displays are presented in close temporal succession at the same location, how does the brain assign them to one versus two conscious percepts? We investigate this issue using a novel reading paradigm in which the odd and even letters of a string are presented alternatively at a variable rate. The results reveal a window of temporal integration during reading, with a nonlinear boundary around approximately 80 msec of presentation duration. Below this limit, the oscillating stimulus is easily fused into a single percept, with all characteristics of normal reading. Above this limit, reading times are severely slowed and suffer from a word-length effect. ERPs indicate that, even at the fastest frequency, the oscillating stimulus elicits synchronous oscillations in posterior visual cortices, while late ERP components sensitive to lexical status vanish beyond the fusion threshold. Thus, the fusion/segregation dilemma is not resolved by retinal or subcortical filtering, but at cortical level by at most 300 msec. The results argue against theories of visual word recognition and letter binding that rely on temporal synchrony or other fine temporal codes.

Fusion of threshold rules for target detection in wireless sensor networks

We propose a binary decision fusion rule that reaches a global decision on the presence of a target by integrating local decisions made by multiple sensors. Without requiring a priori probability of target presence, the fusion threshold bounds derived using Chebyshev's inequality ensure a higher hit rate and lower false alarm rate compared to the weighted averages of individual sensors. The Monte Carlo-based simulation results show that the proposed approach significantly improves target detection performance, and can also be used to guide the actual threshold selection in practical sensor network implementation under certain error rate constraints.

Objective detection of the flicker fusion threshold with pupil diameter and visual evoked magnetic field

Objective detection of the flicker fusion threshold with pupil diameter and visual evoked magnetic field

The Role of Acetaldehyde in Human Psychomotor Function: A Double-Blind Placebo-Controlled Crossover Study

Acetaldehyde, the first product of ethanol metabolization, is a biologically active compound, but the behavioral properties of acetaldehyde in humans are largely undefined. We investigated the acute effects of both alcohol and acetaldehyde on psychomotor functions related to automobile driving skills. Twenty-four men were selected through genotyping; one-half had the ALDH2*1/*1 (active form) genotype and one-half had the ALDH2*1/*2 (inactive form) genotype. In a double-blind placebo-controlled crossover design, each subject was administered one of the following doses of alcohol: .25 g/kg, .5 g/kg, or .75 g/kg or a placebo in four trials that took place at 1-week intervals. Blood ethanol concentration (BEC) and blood acetaldehyde concentration (BAAC) were measured nine times, and psychomotor function tests (critical flicker fusion threshold, choice reaction time, compensatory tracking task, and digit symbol substitution test) were assessed seven times in total over 4 hours after study drug ingestion. After the consumption of alcohol, BEC was comparable in the two subject groups, whereas BAAC was significantly higher in subjects with ALDH2 *1/*2 than in those with ALDH2 *1/*1. The psychomotor performance of subjects with ALDH2*1/*2 was significantly poorer than that of subjects with ALDH2*1/*1. Significant correlations between psychomotor performance and both BEC and BAAC were observed. However, in the linear regression analysis, BAAC significantly predicted poorer psychomotor performance, whereas BEC was not associated with any measure of psychomotor function. Acetaldehyde might be more important than alcohol in determining the effects on human psychomotor function and skills.

Improvement in Intrusion Detection With Advances in Sensor Fusion

Various intrusion detection systems (IDSs) reported in the literature have shown distinct preferences for detecting a certain class of attack with improved accuracy, while performing moderately on the other classes. In view of the enormous computing power available in the present-day processors, deploying multiple IDSs in the same network to obtain best-of-breed solutions has been attempted earlier. The paper presented here addresses the problem of optimizing the performance of IDSs using sensor fusion with multiple sensors. The trade-off between the detection rate and false alarms with multiple sensors is highlighted. It is illustrated that the performance of the detector is better when the fusion threshold is determined according to the Chebyshev inequality. In the proposed data-dependent decision (DD) fusion method, the performance optimization of individual IDSs is first addressed. A neural network supervised learner has been designed to determine the weights of individual IDSs depending on their reliability in detecting a certain attack. The final stage of this DD fusion architecture is a sensor fusion unit which does the weighted aggregation in order to make an appropriate decision. This paper theoretically models the fusion of IDSs for the purpose of demonstrating the improvement in performance, supplemented with the empirical evaluation.

Predicting echo thresholds from speech onset characteristics

Echo threshold variability has previously been examined using stimuli that are carefully controlled and artificial (e.g., clicks and noise bursts), while studies using speech stimuli have only reported average thresholds. To begin to understand how echo thresholds might vary among speech sounds, four syllables were selected in pairs that contrasted abruptness vs gradualness of onset envelopes. Fusion and discrimination suppression thresholds, two echo thresholds commonly used to study the precedence effect, differed among syllables. Results were used to evaluate two predictive heuristics adapted from perceptual center (p-center) models.

ROLE OF STATIC DEFORMATION AND COMPACT ORIENTATION OF TARGET NUCLEUS IN MEASURED FUSION, FUSION-FISSION AND CAPTURE CROSS-SECTIONS OF 244Pu+48Ca REACTION

The dynamical cluster-decay model (DCM), with deformations and orientation degrees of freedom of the incoming nuclei and of outging fragments included, is used to study the excitation functions of the "equatorial" compact hot fusion reaction 244 Pu +48 Ca →292114* (compact orientation angle θc=90° for 244 Pu ). Considering the higher multipole deformations up to hexadecapole deformation β4 and configurations with "compact" orientation θc, the model is shown to give a good description of the measured individual light-particle decay channels σxn, here x=3, 4 and 5, and other decay channels, the fusion-fission σff and quasi-fission σqf (equivalently, capture σ cap ) with in one parameter fitting, the neck length ΔR. The quasi-fission is also considered as a cold process with an elongated "polar" configuration. The xn-channel cross-sections for collisions between nuclei with static deformations at their respective compact orientations are shown to be much more than for the case of the nuclei taken to be spherical, signifying the increase in fusion threshold for an intermediate hot fusion reaction to be associated with the static deformation of the target nucleus and its orientation at the point of collision in its path toward the (spherical) compound nucleus. The shell effects in both the potential and kinetic energy (the mass parameters) terms of the Hamiltonian are shown to be important. The free parameter ΔR of the model is shown to depend strongly on limiting angular momentum, which in turn depends on the use of sticking or non-sticking moment of inertia for angular momentum effects. For the sticking moment of inertia, the evaporation residue (neutron emission) is shown to occur almost promptly (largest ΔR), followed by the competing (hot/cold) quasi-fission and ending finally with fusion-fission of hot compound nucleus. Different ΔR's (equivalently, relative separations) for the three processes means to predict that the processes ER, ff and qf happen in different time-scales, in agreement with the indications of experiments.

The effect of hypoxia on the critical flicker fusion threshold in pilots

Human reactions to environmental changes have been the subject of numerous investigations related to pathophysiology, aviation psychology, aviation, and sports. The present study aimed at evaluating the perception of light stimulus via the Critical Flicker Fusion threshold (CFF) measurements among aviation pilots. The study was carried out under hypoxic conditions corresponding to 5000 m altitude, for a period of 30 min, without the use of supplemental oxygen. Fourteen volunteer pilots, 23-30 years of age, were examined in the hypobaric chamber (HC). The measurements were performed at normobaria and at the initial and final phase of hypoxia. Heart rate (HR) and blood oxygen saturation (SaO2) were monitored. The high altitude hypoxia was found to produce a decrease in the CFF threshold F(3.39) = 3.207, p < 0.05, and SaO2 F(3.39) = 52.651, p < 0.001, as well as HR increase F(3.39) = 7.356, p < 0.001. The results indicate that the higher the decrease in SaO2 under hypoxic conditions, the higher the decrease in CFF r = .567 p < 0.05. Likewise, the higher the increase in HR, the higher the decrease in CFF r = -0.491 p < 0.05. Under hypoxic conditions, the perceptual ability of the pilots is gradually decreasing. This has been confirmed by the findings of the physiological examinations. The authors express an opinion that it would be advisable to introduce CFF measurement into the hypobaric chamber tests as it allows individual assessment of the pilot's perceptual ability under conditions of incomplete physiological compensation of the high altitude hypoxia.

Non-arbitrary detection of the flicker fusion threshold with pupil diameter and visual evoked magnetic field

Non-arbitrary detection of the flicker fusion threshold with pupil diameter and visual evoked magnetic field

Numerical-Experimental Study and Solutions to Reduce the Dwell-Time Threshold for Fusion-Free Consecutive Injections in a Multijet Solenoid-Type CR System

In “multijet” common rail (CR) diesel injection systems, when two consecutive injection current pulses approach each other, a merging of the two injections into a single one can occur. Such an “injection fusion” causes an undesired excessive amount of injected fuel, worsening both fuel consumption and particulate emissions. In order to avoid this phenomenon, lower limits to the dwell-time values are introduced in the control unit maps by a conservatively overestimated threshold, which reduces the flexibility of multiple-injection management. The injection fusion occurrence is mainly related to the time delay between the electrical signal to the solenoid and the nozzle opening and closure. The dwell-time fusion threshold was found to strongly decrease particularly with the nozzle closure delay. A functional dependence of the nozzle opening and closure delays on the solenoid energizing time and nominal rail pressure was experimentally assessed, and the injection temporal duration was correlated to the energizing time and rail pressure. A multijet CR injection-system mathematical model that was previously developed, including thermodynamics of liquids, fluid dynamics, mechanics of subsystems, and electromagnetism equations, was applied to better understand the cause and effect relationships for nozzle opening and closure delays. In particular, numerical results on the time histories of delivery- and control-chamber pressures, pilot- and needle-valve lifts, and mass flow rates through Z and A holes were obtained and analyzed to highlight the dependence of nozzle opening and closure delays on injector geometric features, physical variables, and valve dynamics. The nozzle closure delay was shown to strongly depend on the needle dynamics. Parametric numerical tests were carried out to identify configurations useful for minimizing the nozzle closure delay. Based on the results of these tests, a modified version of a commercial electroinjector was built, so as to achieve effectively lower nozzle closure delays and very close sequential injections without any fusion between them.

A Double-blind Placebo-controlled Investigation of the Psychomotor Profile of Clopidogrel in Healthy Volunteers

Clopidogrel is a thienopyridine antiplatelet agent that inhibits adenosine diphosphate-dependent platelet activation and aggregation and is currently one of the most widely prescribed antiplatelet drugs for the treatment of symptomatic coronary artery disease. Several large clinical trials have demonstrated that it has a potent protective effect against adverse vascular events, including coronary, cerebral, and peripheral arterial disease. These clinical trials have reported among other clopidogrel's adverse effects, the adverse effects related to the central nervous system including headache and dizziness occurring in 7.6% and 6.2% of patients, respectively. Aim of this study is to detect possible effect of clopidogrel on human psychomotor performance in healthy volunteers. Using a double-blind, placebo-controlled, balanced, between-subject design at laboratories of the pharmacology department in Al-Mustansiryiah University Medical College, Baghdad, Iraq, during the academic year 2007-2008. Fifty-four young healthy volunteers were enrolled, they received either single oral doses of clopidogrel 37.5 mg (Plavix; Sanofi-Synthelabo) or placebo. Each treatment was given to 27 subjects. Measurements of psychomotor performance including the choice reaction time and its 2 components, recognition reaction time and movement reaction time, and the critical flicker fusion threshold using the computerized Leed psychomotor tester were performed just before medication and 2 hours afterward. No statistically significant difference in the parameters measured was detected among the two treatment groups. In this study, we found that single oral doses of clopidogrel in our group of normal healthy volunteers did not affect their psychomotor performance.

The combined effects of L-theanine and caffeine on cognitive performance and mood

The aim of this study was to compare 50 mg caffeine, with and without 100 mg L-theanine, on cognition and mood in healthy volunteers. The effects of these treatments on word recognition, rapid visual information processing, critical flicker fusion threshold, attention switching and mood were compared to placebo in 27 participants. Performance was measured at baseline and again 60 min and 90 min after each treatment (separated by a 7-day washout). Caffeine improved subjective alertness at 60 min and accuracy on the attention-switching task at 90 min. The L-theanine and caffeine combination improved both speed and accuracy of performance of the attention-switching task at 60 min, and reduced susceptibility to distracting information in the memory task at both 60 min and 90 min. These results replicate previous evidence which suggests that L-theanine and caffeine in combination are beneficial for improving performance on cognitively demanding tasks.

A method for achieving an order-of-magnitude increase in the temporal resolution of a standard CRT computer monitor

As the frequency of a flickering light is increased, the perception of flicker is replaced by the perception of steady light at what is known as the critical flicker fusion threshold (CFFT). This threshold provides a useful measure of the brain's information processing speed, and has been used in medicine for over a century both for diagnostic and drug efficacy studies. However, the hardware for presenting the stimulus has not advanced to take advantage of computers, largely because the refresh rates of typical monitors are too slow to provide fine-grained changes in the alternation rate of a visual stimulus. For example, a cathode ray tube (CRT) computer monitor running at 100Hz will render a new frame every 10ms, thus restricting the period of a flickering stimulus to multiples of 20ms. These multiples provide a temporal resolution far too low to make precise threshold measurements, since typical CFFT values are in the neighborhood of 35ms. We describe here a simple and novel technique to enable alternating images at several closely-spaced periods on a standard monitor. The key to our technique is to programmatically control the video card to dynamically reset the refresh rate of the monitor. Different refresh rates allow slightly different frame durations; this can be leveraged to vastly increase the resolution of stimulus presentation times. This simple technique opens new inroads for experiments on computers that require more finely-spaced temporal resolution than a monitor at a single, fixed refresh rate can allow.

Fusion and masking threshold of a tone in narrowband noise

When comparing different pitch phenomena, it is not clear whether the expression pitch strength points towards a unique perceptive phenomenon or object. As many studies concentrate on one special phenomenon, the question, what is actually judged, seems only implicitly answered. Kubovy and Van Valkenburg (2001) define a perceptual object as "that what is susceptible to figure-ground segregation". Pitch plays a major role in these grouping processes. In this context the judgment of pitch strength refers to two perceptual cases. The first one is the pitch strength of a tone-in-noise, i.e. the case where the pitch is linked to a separate contour within the narrowband noise (NBN), while the second is the pitch strength of tonal noise. Here, the noise evokes a pitch sensation that is not related to a separate object. In order to explore the transition from case /1 tone-in-noise to case /2 tonal noise, the identification threshold hearing a tone in NBN centered on the tone is determined in a lab experiment. This segregation or fusion threshold is compared to the measured masking threshold for center frequencies 250-4000 Hz octave-wise at 60 dB SPL noise level. The bandwith of the NBN is varied from 50-250 Hz accordingly.