Individual Detection Thresholds Research Articles

Binaural detection thresholds and audio quality of speech and music signals in complex acoustic environments.

Every-day acoustical environments are often complex, typically comprising one attended target sound in the presence of interfering sounds (e.g., disturbing conversations) and reverberation. Here we assessed binaural detection thresholds and (supra-threshold) binaural audio quality ratings of four distortions types: spectral ripples, non-linear saturation, intensity and spatial modifications applied to speech, guitar, and noise targets in such complex acoustic environments (CAEs). The target and (up to) two masker sounds were either co-located as if contained in a common audio stream, or were spatially separated as if originating from different sound sources. The amount of reverberation was systematically varied. Masker and reverberation had a significant effect on the distortion-detection thresholds of speech signals. Quality ratings were affected by reverberation, whereas the effect of maskers depended on the distortion. The results suggest that detection thresholds and quality ratings for distorted speech in anechoic conditions are also valid for rooms with mild reverberation, but not for moderate reverberation. Furthermore, for spectral ripples, a significant relationship between the listeners' individual detection thresholds and quality ratings was found. The current results provide baseline data for detection thresholds and audio quality ratings of different distortions of a target sound in CAEs, supporting the future development of binaural auditory models.

A study on the relationship between odor hedonic ratings and individual odor detection threshold

Odor hedonic perception (pleasant/unpleasant character) is considered as the first and one of the most prominent dimensions in olfaction and is known to depend on several parameters. Among them, the relation between the odorant concentration and the hedonic estimation has been widely studied. However, few studies have considered odor hedonic ratings (OHR) in relation to individual detection thresholds (IDT). Thus, the aim of this study was to determine olfactory detection thresholds and to describe hedonic rating variations from individual thresholds to higher concentrations. IDT were performed for two pleasant (apple and jasmine) and two unpleasant (durian and trimethylamine) odorant stimuli. The experimenter presented one by one in a randomized order, the different odorant concentrations above IDT. Participants rated odor hedonic valence of these stimuli on a visual analog scale. Results showed, except for trimethylamine, the same relationship between hedonic ratings and stimulus concentration, i.e., an increase of pleasantness (apple and jasmine)/unpleasantness (durian) ratings at low and middle concentrations followed by a plateau at high concentrations. Correlations between OHR and concentrations as well as between OHR and threshold steps were always significant. Moreover, comparisons between both conditions showed that the correlation coefficient was significantly higher for trimethylamine (and a trend for apple) when IDTs were considered, while no difference was found for jasmine and durian. Overall, results suggested that the relationship between OHR and IDT is odor specific. These findings contribute to explain the large variability of the hedonic tone (i.e., weakly vs. very pleasant, weakly vs. very unpleasant) at specific concentration in the general population and could serve future research in this field (e.g., olfactory preferences in nutrition studies, anhedonia in psychiatric disorders…).

An Exploratory Investigation of Pupillometry As a Measure of Tinnitus Intrusiveness on a Test of Auditory Short-Term Memory.

The purpose of the current study was to investigate the potential of pupillometry to provide an objective measure of competition between tinnitus and external sounds during a test of auditory short-term memory. Twelve participants with chronic tinnitus and twelve control participants without tinnitus took part in the study. Pretest sessions used an adaptive method to estimate listeners' frequency discrimination threshold on a test of delayed pitch discrimination for pure tones. Target and probe tones were presented at 72 dB SPL and centered on 750 Hz±2 semitones with an additional jitter of 5 to 20 Hz. Test sessions recorded baseline pupil diameter and task-related pupillary responses (TEPRs) during three blocks of delayed pitch discrimination trials. The difference between target and probe tones was set to the individual's frequency detection threshold for 80% response-accuracy. Listeners with tinnitus also completed the Tinnitus Handicap Inventory (THI). Linear mixed effects procedures were applied to examine changes in baseline pupil diameter and TEPRs associated with group (tinnitus versus control), block (1 to 3) and their interaction. The association between THI scores and maximum TEPRs was assessed using simple linear regression. Patterns of baseline pupil dilation across trials diverged in listeners with tinnitus and controls. For controls, baseline pupil dilation remained constant across blocks. For listeners with tinnitus, baseline pupil dilation increased on blocks 2 and 3 compared with block 1. TEPR amplitudes were also larger in listeners with tinnitus than controls. Linear mixed effects models yielded a significant group by block interaction for baseline pupil diameter and a significant main effect of group on maximum TEPR amplitudes. Regression analyses yielded a significant association between THI scores and TEPR amplitude in listeners with tinnitus. Our data indicate measures of baseline pupil diameter, and TEPRs are sensitive to competition between tinnitus and external sounds during a test of auditory short-term memory. This result suggests pupillometry can provide an objective measure of intrusion in tinnitus. Future research will be required to establish whether our findings generalize to listeners across a full range of tinnitus severity.

Effects of glaucoma on detection and discrimination of image blur.

PurposeBlur is one of the most commonly reported visual symptoms of glaucoma, but it is not directly measured by current clinical tests. We aimed to investigate the effects of glaucoma on detection and discrimination of image blur.MethodsParticipants were people with glaucoma, separated into two groups with (n = 15) or without (n = 17) central visual field defects measured by 10–2 perimetry, and an age‐similar control group (n = 18). First, we measured contrast detection thresholds centrally using a 2‐interval forced choice procedure. We then measured blur detection and discrimination thresholds for the same stimuli (reference blurs 0, 1 arcmin) using a 2‐alternative forced choice procedure under two contrast conditions: 4× individual detection threshold for the low contrast condition; 95% contrast for the high contrast condition. The stimulus was a horizontal edge bisecting a hard‐edged circle of 4.5° diameter. Data were analysed by linear mixed modelling.ResultsContrast detection thresholds for the glaucoma group with central visual field defects were raised by 0.01 ± 0.004 (mean ± SE, Michelson units) (p = 0.002) and by 0.01 ± 0.004 (p = 0.03) relative to control and glaucoma without central visual field defect groups, respectively. Blur detection and discrimination thresholds were similar between groups, with small elevations in blur detection thresholds in the glaucoma groups not reaching statistical significance (detection p = 0.29, discrimination p = 0.91). The lower contrast level increased thresholds from the higher contrast level by 1.30 ± 0.10 arcmin (p < 0.001) and 1.05 ± 0.10 arcmin (p < 0.001) for blur detection and discrimination thresholds, respectively.ConclusionsEarly‐moderate glaucoma resulted in only minimal elevations of blur detection thresholds that did not reach statistical significance in this study. Despite the prevalence of blur as a visual symptom of glaucoma, psychophysical measurements of blur detection or discrimination may not be good candidates for development as clinical tests for glaucoma.

Human detection thresholds of DC, AC, and hybrid electric fields: a double-blind study

BackgroundIn the course of the ongoing transition of electric energy systems, transmission corridors are often upgraded to higher voltages and other technologies leading to another quality of human exposure. The study aims to determine human detection thresholds for direct current (DC), alternating current (AC), and hybrid electric fields (various DC; constant AC).MethodsA total of 203 participants were exposed to DC, AC, and hybrid electric fields (EFs) in a highly specialized whole-body exposure laboratory using a double-blind experimental setting. Additionally, the participants were exposed to ion currents in part of the DC and hybrid sessions. To investigate environmental influences, relative humidity was changed in two subgroups during EF perception. Methods derived from the signal detection theory and the adaptive staircase procedure based on the single interval adjustment matrix were used to assess individual sensitivity and detection thresholds, respectively.ResultsThe results indicated that detection thresholds of hybrid EF were lower compared to single EF presentation of DC or AC. Ion current exposure enhanced EF perception. High relative humidity facilitated DC EF perception, whereas low relative humidity reinforced the perception of AC EFs.ConclusionsWith this systematic investigation of human perception of DC, AC, and hybrid EFs, detection thresholds were provided, which can help improve the construction processes of energy transmission systems and the prevention of unwanted sensory perception by contributing to the determination of limit values.

Task-dependent audiovisual temporal sensitivity is not affected by stimulus intensity levels

Flexibility and robustness of multisensory temporal recalibration is paramount for maintaining perceptual constancy of the surrounding natural world. Different environments impart various impediments, distances and routes that alter the propagation times of sight and sound cues comprising a multimodal event. One’s ability to rapidly calibrate and account for these external variations allows for maintained perception of synchrony which is crucial for coherent and consistent perception. The two common paradigms used to compare precision of temporal processing between experimental and control groups, the simultaneity judgment (SJ) and temporal order judgment (TOJ) tasks, often use supra-threshold stimuli. However, few studies have specifically examined the effects of normalizing stimulus intensities to participant’s unisensory detection thresholds. The current project presented multiple combinations of auditory and visual stimulus intensity levels, based on individual detection thresholds, during a TOJ and a SJ task. While no effect of stimulus intensity was found on temporal sensitivity or perceived temporal synchrony, there was a significant difference in point of subjective simultaneity (PSS) measures between tasks. In addition, PSS estimates were audio-leading, rather than visual-leading as previously reported, suggesting that exposure to the particular combinations of stimulus intensity levels used influenced temporal synchrony perception. Overall, these results support the use of supra-threshold stimuli in TOJ and SJ tasks as a way of minimizing the confound from differences in unisensory processing.

CopyDetective: Detection threshold-aware copy number variant calling in whole-exome sequencing data.

BackgroundCopy number variants (CNVs) are known to play an important role in the development and progression of several diseases. However, detection of CNVs with whole-exome sequencing (WES) experiments is challenging. Usually, additional experiments have to be performed.FindingsWe developed a novel algorithm for somatic CNV calling in matched WES data called “CopyDetective". Different from other approaches, CNV calling with CopyDetective consists of a 2-step procedure: first, quality analysis is performed, determining individual detection thresholds for every sample. Second, actual CNV calling on the basis of the previously determined thresholds is performed. Our algorithm evaluates the change in variant allele frequency of polymorphisms and reports the fraction of affected cells for every CNV. Analyzing 4 WES data sets (n = 100) we observed superior performance of CopyDetective compared with ExomeCNV, VarScan2, ControlFREEC, ExomeDepth, and CNV-seq.ConclusionsIndividual detection thresholds reveal that not every WES data set is equally apt for CNV calling. Initial quality analyses, determining individual detection thresholds—as realized by CopyDetective—can and should be performed prior to actual variant calling.

A psychoacoustical study to investigate the perceived unpleasantness of infrasound combined with audio-frequency sound

At many immission sites of infrasound (frequency f &lt; 20 Hz), humans are exposed to a mixture of infrasound and sound in the common audio-frequency range (audio sound, 20 Hz &lt; f &lt; 20 kHz). Therefore, the purpose of this study was to examine the auditory perception of infrasound and audio sound not only in isolation but also in combination. This laboratory study aims to investigate the perceived unpleasantness of infrasound (sinusoid at 12 Hz) and audio sound (sinusoid at 1000 Hz, pink-noise 250–4000 Hz), presented alone or in combination with each other. A pairwise comparison task and a rating task using a numerical scale were conducted with 19 normal hearing listeners. In addition, individual detection thresholds were determined for the infrasound stimulus. Combinations of infrasound and audio sound were rated as equally or more unpleasant than either sound presented alone. Inter-individual differences in unpleasantness ratings using the numerical scale were particularly high for stimuli containing infrasound. This can only in part be related to the large variability in infrasound thresholds. These findings suggest that simultaneous exposure to infrasound and audio sound can increase the perceived unpleasantness when both are presented at a sufficient level above the detection threshold.

Oil Perception-Detection Thresholds for Varying Fatty Stimuli and Inter-individual Differences.

Multiple lines of research have demonstrated that humans can perceive fat in the form of free fatty acids (FFAs). However, the dietary concentration of FFAs is generally very low and fat is mainly consumed as triacylglycerol (TAG). The aim of this study was to examine the perception of different fatty stimuli and possible associations between them. Therefore, detection thresholds for 4 fatty stimuli (oleic acid [FFA], paraffin oil [mixture of hydrocarbon molecules], canola oil [TAG-rich], and canola oil spiked with oleic acid [rich in TAGs and FFAs]) were determined in 30 healthy participants. Additionally, inter-individual differences in fat perception were examined. It was observed that oleic acid was perceivable at significantly lower concentrations than all other stimuli (P < 0.001). Similarly, canola oil with oleic acid was detectable at lower concentrations than canola oil alone (P < 0.001). Moreover, canola oil detection thresholds were significantly lower than paraffin oil detection thresholds (P = 0.017). Participants who were sensitive for low concentrations for oleic acid showed lower detection thresholds for canola oil with and without oleic acid, compared with participants that were less sensitive for oleic acid. The results of this study demonstrate that the higher the concentrations of FFAs in the stimuli, the lower the individual fat detection threshold. Moreover, participants being sensitive for lower concentrations of FFAs are also more likely to detect low concentrations of TAG-rich fats as it is found in the human diet.

Energy-Efficient Joint Sensing Duration, Detection Threshold, and Power Allocation Optimization in Cognitive OFDM Systems

This paper investigates an energy efficiency optimization problem in cognitive orthogonal frequency division multiplexing systems. The goal is to maximize the energy efficiency by adapting the sensing duration, detection threshold, and transmit power to the constraints of the energy consumption of the secondary network and the interference to the primary network in a statistical manner. First, the case of identical detection threshold for all subcarriers is considered. In order to circumvent the intractability of the resulting problem, an alternate iteration framework is proposed to iteratively solve the three decoupled subproblems: sensing duration optimization, detection threshold optimization, and power allocation optimization. By exploiting the characteristics of each subproblem, the proposed framework is proved to be convergent. Then, the case with individual detection threshold for each subcarrier is explored. By proving that the optimal detection threshold is the root of a quadratic equation with one unknown variable, the proposed framework can be applied with minor modification. Simulation results show that the proposed alternating optimization framework can approach rapidly to the optimal solution, with less than 1% gap. Compared with the existing schemes, both the cases with identical and individual detection thresholds can achieve a considerable energy efficiency gain, with the latter further outperforming the former.

EP 68. Stochastic resonance in the vestibular system

Stochastic resonance (SR) is a phenomenon, wherein the response of a nonlinear system to weak input signals can be optimized by addition of a particular non-zero level of noise. Here we tested for the presence of SR in the vestibular system by evaluating if a white noise galvanic vestibular stimulation (GVS) lowers the vestibular detection threshold. Sixteen healthy subjects (mean age 28.9 ± 2.0 years) participated in the study. Vestibular threshold detection was done by identifying the amplitude of a 1 Hz sinusoidal GVS (Digitimer, Hertfordshire, UK) at which subjects exhibit motion induced by the stimulation. Threshold detection was performed without and with an additional white noise GVS within a frequency range of 0–30 Hz and an amplitude set to 80% of the individual cutaneous threshold for GVS. Each threshold detection task consisted in ten bipolar sinusoidal GVS trials with amplitudes ranging from 0.1 μA to 1.9 μA (0.2 μA steps) while subjects sat on a chair with their eyes closed. Body motion was recorded via two inertial sensors (APDM, Inc., Portland, OR) fixed on the head and the trunk and motion responses were counted whenever the motion amplitude exceeded two standard deviations from mean calculated during a resting period preceding each stimulation trial. Body motion responses to stimulation were normalized with respect to the largest response value across all stimulation trials. A binomial distribution function was fit to the GVS amplitude and body response data and the detection was then determined as the stimulation amplitude at the point of subjective equality (i.e., a 50% chance of motion detection). The total of 20 stimulation trials was examined in a random order and subjects were blinded to the protocol. Individual detection thresholds without and with white noise GVS were compared using a paired samples t-test. White noise GVS significantly lowered vestibular detection thresholds from 1.02 ± 0.06 μA to 0.87 ± 0.04 μA (p = 0.011). The mean improvement was 7.9 ± 5.9%. White noise GVS has been previously found to improve cardiac function, postural control, and dynamic walking stability in healthy subjects and patients with bilateral vestibular dysfunction as well as Parkinson’s disease. The present findings indicate that the previously observed ameliorating effects of white noise GVS might result from an enhanced vestibular information processing and provide thereby first evidence for the presence of SR phenomena in the vestibular system.

Auditory temporal resolution is linked to resonance frequency of the auditory cortex

A brief silent gap embedded in an otherwise continuous sound is missed by a human listener when it falls below a certain threshold: the gap detection threshold. This can be interpreted as an indicator that auditory perception is a non-continuous process, during which acoustic input is fragmented into a discrete chain of events. Current research provides evidence for a covariation between rhythmic properties of speech and ongoing rhythmic activity in the brain. Therefore, the discretization of acoustic input is thought to facilitate speech processing. Ongoing oscillations in the auditory cortex are suggested to represent a neuronal mechanism which implements the discretization process and leads to a limited auditory temporal resolution. Since gap detection thresholds seem to vary considerably between individuals, the present study addresses the question of whether individual differences in the frequency of underlying ongoing oscillatory mechanisms can be associated with auditory temporal resolution. To address this question we determined an individual gap detection threshold and a preferred oscillatory frequency for each participant. The preferred frequency of the auditory cortex was identified using an auditory steady state response (ASSR) paradigm: amplitude-modulated sounds with modulation frequencies in the gamma range were presented binaurally; the frequency which elicited the largest spectral amplitude was considered the preferred oscillatory frequency. Our results show that individuals with higher preferred auditory frequencies perform significantly better in the gap detection task. Moreover, this correlation between oscillation frequency and gap detection was supported by high test–retest reliabilities for gap detection thresholds as well as preferred frequencies.

MEASURING GALAXY CLUSTERING AND THE EVOLUTION OF [C II] MEAN INTENSITY WITH FAR-IR LINE INTENSITY MAPPING DURING 0.5 &lt;z&lt; 1.5

Infrared fine-structure emission lines from trace metals are powerful diagnostics of the interstellar medium in galaxies. We explore the possibility of studying the redshifted far-IR fine-structure line emission using the three-dimensional (3D) power spectra obtained with an imaging spectrometer. The intensity mapping approach measures the spatio-spectral fluctuations due to line emission from all galaxies, including those below the individual detection threshold. The technique provides 3D measurements of galaxy clustering and moments of the galaxy luminosity function. Furthermore, the linear portion of the power spectrum can be used to measure the total line emission intensity including all sources through cosmic time with redshift information naturally encoded. Total line emission, when compared to the total star formation activity and/or other line intensities, reveals evolution of the interstellar conditions of galaxies in aggregate. As a case study, we consider measurement of [C ii] autocorrelation in the 0.5 < z < 1.5 epoch, where interloper lines are minimized, using far-IR/submillimeter balloon-borne and future space-borne instruments with moderate and high sensitivity, respectively. In this context, we compare the intensity mapping approach to blind galaxy surveys based on individual detections. We find that intensity mapping is nearly always the best way to obtain the total line emission because blind, wide-field galaxy surveys lack sufficient depth and deep pencil beams do not observe enough galaxies in the requisite luminosity and redshift bins. Also, intensity mapping is often the most efficient way to measure the power spectrum shape, depending on the details of the luminosity function and the telescope aperture.

Detection threshold for sound distortion resulting from noise reduction in normal-hearing and hearing-impaired listeners.

Hearing-aid noise reduction should reduce background noise, but not disturb the target speech. This objective is difficult because noise reduction suffers from a trade-off between the amount of noise removed and signal distortion. It is unknown if this important trade-off differs between normal-hearing (NH) and hearing-impaired (HI) listeners. This study separated the negative effect of noise reduction (distortion) from the positive effect (reduction of noise) to allow the measurement of the detection threshold for noise-reduction (NR) distortion. Twelve NH subjects and 12 subjects with mild to moderate sensorineural hearing loss participated in this study. The detection thresholds for distortion were determined using an adaptive procedure with a three-interval, two-alternative forced-choice paradigm. Different levels of distortion were obtained by changing the maximum amount of noise reduction. Participants were also asked to indicate their preferred NR strength. The detection threshold for overall distortion was higher for HI subjects than for NH subjects, suggesting that stronger noise reduction can be applied for HI listeners without affecting the perceived sound quality. However, the preferred NR strength of HI listeners was closer to their individual detection threshold for distortion than in NH listeners. This implies that HI listeners tolerate fewer audible distortions than NH listeners.

Luminosity function of low-mass X-ray binaries in the globular cluster system of NGC 1399

We present a study of the faint-end of the X-ray Luminosity Function of Low Mass X-ray binaries in the Globular Cluster system of the cD galaxy NGC 1399 by performing a stacking experiment on 618 X-ray undetected GCs, in order to verify the presence of faint LMXBs and to constrain the faint-end slope of the GC-LMXBs XLF below the individual detection threshold of $8\times10^{37}$ erg s$^{-1}$ in the $0.5-8$ keV band. We obtain a significant X-ray detection for the whole GC sample, as well as for the red and blue GC subpopulations, corresponding to an average luminosity per GC $<L_{X}>_{GC}$ of $(3.6\pm1.0)\times10^{36}\ erg\ s^{-1}$, $(6.9\pm2.1)\times10^{36}\ erg\ s^{-1}$ and $(1.7\pm0.9)\times10^{36}\ erg\ s^{-1}$, respectively for all, red and blue GCs. If LMXBs in red and blue GCs have the same average intrinsic luminosity, we derive a red/blu ratio $\simeq 3$ of GCs hosting LMXBs ($2.5\pm1.0$ or $4.1\pm2.5$ depending on the surveyed region); alternatively, assuming the fractions observed for brighter sources, we measure an average X-ray luminosity of $L_{X}=(4.3\pm1.3)\times10^{37}\ erg\ s^{-1}$ and $L_{X}=(3.4\pm1.7)\times10^{37}\ erg\ s^{-1}$ per red and blue GC-LMXBs respectively. In the assumption that the XLF follows a power-law distribution, we find that a low-luminosity break is required at $L_{X}\leq 8\times10^{37}$ erg s$^{-1}$ both in the whole, as well as in the color-selected (red and blue) subsamples. Given the bright-end slopes measured above the X-ray completeness limit, this result is significant at $>3\sigma$ level. Our best estimates for the faint end slope are $\beta_{L}=-1.39/-1.38/-1.36$ for all/red/blue GC-LMXBs. We also find evidence that the luminosity function becomes steeper at luminosities $L_X\gtrsim 3\times 10^{39}$ erg s$^{-1}$, as observed in old ellipticals.

Analysis of Joint Multiband Sensing-Time M-QAM Signal Detection in Cognitive Radios

We analyze a wideband spectrum in a cognitive radio (CR) network by employing the optimal adaptive multiband sensing-time joint detection framework. This framework detects a wideband M-ary quadrature amplitude modulation (M-QAM) primary signal over multiple nonoverlapping narrowband Gaussian channels, using the energy detection technique so as to maximize the throughput in CR networks while limiting interference with the primary network. The signal detection problem is formulated as an optimization problem to maximize the aggregate achievable secondary throughput capacity by jointly optimizing the sensing duration and individual detection thresholds under the overall interference imposed on the primary network. It is shown that the detection problems can be solved as convex optimization problems if certain practical constraints are applied. Simulation results show that the framework under consideration achieves much better performance for M-QAM than for binary phase-shift keying or any real modulation scheme.

The influence of salt taste threshold on acceptability and purchase intent of reformulated reduced sodium vegetable soups

Evidence suggests a link between an individual’s salt taste sensitivity and their acceptance and consumption of salty foods. Individuals who consume a high salt diet appear to require a higher concentration of salt to obtain the same taste sensation as those less sensitive to salt. Therefore, in the present study the influence of salt taste threshold on the acceptability and subsequent purchase intent of a number of reformulated reduced salt vegetable soups was examined. Detection and recognition thresholds of salt taste in 60 consumers were measured via ingestion of a series of salt water solutions. The same 60 consumers then evaluated five vegetable soup samples, four of which had reduced salt concentrations (∼0.45%) and one which had regular commercial salt concentrations (0.93%). A nine point hedonic acceptability scale and a five point purchase intent scale were used to rate the samples. Individual detection and recognition thresholds had no significant effect (p>0.05) on acceptability or purchase intent scores for any of the vegetable soup samples. However, salt detection thresholds were found to differ significantly (p<0.05) between male (n=26) and female (n=34) consumers. Significant correlations were observed between vegetable soup acceptability scores and purchase intent ratings of the same samples (r=0.814; p=0.000). These results highlight the importance of both taste characteristics and the inclusion of the consumer in the reformulation process of reduced salt foods. The study also shows that salt reductions of up to 48% can be achieved in commercial vegetable soup samples without affecting consumers liking for the meal.

Multivariate pattern analysis of evoked brain potentials by temporal matching pursuit and support vector machine

Abstract Background/aims Electroencephalography (EEG) recorded as evoked brain potentials (EPs) reflects the cortical processing to an external event. This approach is often used to study the altered response to acute pain in chronic pain patients compared to healthy volunteers. However, discrimination of the responses from the study populations is a non-trivial task, which calls for improved objective methods. Methods To develop and validate a new methodology, we analyzed data from 16 type-1 diabetes mellitus patients and 15 age and gender matched volunteers, by means of brain activity recorded from 62 EEG channels. The EEG signals were recorded as EPs elicited by painful electrical stimulations in the oesophagus with an intensity corresponding to the individual pain detection threshold. The EPs from all channels and subjects were decomposed simultaneously by a temporal matching pursuit (TMP) algorithm with Gabor atoms. Results Amplitude and phase features were classified by a support vector machine (SVM) to discriminate patients from healthy volunteers. A classification performance of 93.1% (P&lt;0.001) was obtained when applying a majority voting scheme to the 3 best performing channels (FC4, C1, and C6) and including features from 2 atoms. The most discriminative features were determined by the slope coefficients from the SVM decision rule, which identified the biomarkers as delayed latency of the first atom (N2–P2 complex) and decreased amplitude of the second atom (NI–P1 complex). Conclusion The combination of TMP and SVM is a novel approach to classify two study populations, which may provide a new objective tool to identify biomarkers from various chronic pain populations.

Cross-correlating the thermal Sunyaev-Zel’dovich effect and the distribution of galaxy clusters

We present the analytical formulas, derived based on the halo model, to compute the cross-correlation between the thermal Sunyaev-Zel'dovich (SZ) effect and the distribution of galaxy clusters. By binning the clusters according to their redshifts and masses, this cross-correlation, the so-called stacked SZ signal, reveals the average SZ profile around the clusters. The stacked SZ signal is obtainable from a joint analysis of an arcminute-resolution cosmic microwave background (CMB) experiment and an overlapping optical survey, which allows for detection of the SZ signals for clusters whose masses are below the individual cluster detection threshold. We derive the error covariance matrix for measuring the stacked SZ signal, and then forecast for its detection from ongoing and forthcoming combined CMB-optical surveys. We find that, over a wide range of mass and redshift, the stacked SZ signal can be detected with a significant signal to noise ratio (total S/N \gsim 10), whose value peaks for the clusters with intermediate masses and redshifts. Our calculation also shows that the stacking method allows for probing the clusters' SZ profiles over a wide range of scales, even out to projected radii as large as the virial radius, thereby providing a promising way to study gas physics at the outskirts of galaxy clusters.

An electrophysiological study of conscious visual perception using progressively degraded stimuli

Previous event-related potential (ERP) studies have provided mixed results regarding the earliest manifestations of conscious visual report. One possible explanation for the results could be that conscious visual perception emerges progressively rather than appearing as a binary transition. In the present study, we used electrical neuroimaging to identify the stages of processing that lead to the successful conscious identification of a briefly presented degraded stimulus. Grayscale images of faces and butterflies were presented for 16 ms and their visibility was manipulated by means of random image structure evolution (RISE). Three levels of RISE image distortions were used for each image. First, we determined an individual detection threshold of 50% for each subject. We then added two control conditions, namely fully degraded stimuli and stimuli that yielded 80% detection. Topographic ERP analyses revealed distinct effects for identified and unidentified stimuli at the threshold of detection. Four stages were observed that distinguished successful from unsuccessful stimulus identification. This shows that the events associated with conscious perception occurs at several distinct stages in time starting as early as 220 ms after stimulus presentation, rather than translating as a single temporal event and includes marked top-down activations when identification becomes difficult.