Transient and sustained BOLD responses to sustained visual stimulation

Examining the transients of the blood-oxygenation-level-dependent (BOLD) signal using functional magnetic resonance imaging is a tool to probe basic brain physiology. In addition to the so-called initial dip and poststimulus undershoot of the BOLD signal, occasionally, overshoot at the beginning and at the end of stimulation and stimulus onset and offset ('phasic') responses are observed. Hemifield visual stimulation was used in human subjects to study the latter transients. As expected, sustained ('tonic') stimulus-correlated contralateral activation in the visual cortex and LGN was observed. Interestingly, bilateral phasic responses were observed, which only partly overlapped with the tonic network and which would have been missed using a standard analysis. A biomechanical model of the BOLD signal ('balloon model') indicated that, in addition to phasic neuronal activity, vascular uncoupling can also give rise to phasic BOLD signals. Thus, additional physiological information (i.e., cerebral blood flow) and examination of spatial distribution of the activity might help to assess the BOLD signal transients correctly. In the current study, although vascular uncoupled responses cannot be ruled out as an explanation of the observed phasic BOLD network, the spatial distribution argues that sustained hemifield visual stimulation evokes both bilateral phasic and contralateral sustained neuronal responses. As a consequence, in rapid event-related experimental designs, both the phasic and tonic networks cannot be separated, possibly confounding the interpretation of BOLD signal data. Furthermore, a combination of phasic and tonic responses in the same region of interest might also mimic a BOLD response typically observed in adaptation experiments.     

Auditory hazard from airbag noise exposure

Airbag deployment includes very intense acoustic stimulation, yet almost no tests of auditory hazard have been done with real ears. Therefore 32 anesthetized cats, positioned at the driver and passenger locations in a pickup truck, were exposed in pairs to one airbag deployment (electrically initiated). Hearing was tested at 1, 2, 4, 8, and 16 kHz by evoked-response audiometry just before exposure, immediately after and at 1 month and 6 months. Exposure conditions included doors open, compartment closed, and closed compartment sealed with tape: seven exposures to passenger bag only and nine to driver and passenger bags. Peak pressures ranged from 167 to 173 dB with unweighted energies as high as 4000 J/m2 (or 8 hr LEQA = 95.5 dB). The immediate threshold shift averaged 60 dB at 4.0 kHz that resolved to an average permanent shift of 37 dB. By extrapolation, these data from cats may indicate that susceptible human ears risk permanent hearing loss from airbag noise.     

A memory device sustained by noise

We propose a memory device consisting of a ring of two bistable coupled oscillators. We show that this system is capable of storing a single bit and its performance improves with noise, in agreement with previous experimental results obtained with discrete bistable electronic circuits. The stored bit can be retrieved asynchronously and, after a certain synchronization time, the probability of error does not depend on the interrogated oscillator. Memory persistence is shown to be maximized for the same noise range that both minimizes the probability of error and ensures synchronization.     

Subjective responses of Chinese to aircraft noise

A social study was undertaken of the subjective responses to aircraft noise of 909 Chinese in Hong Kong. The study population lives near, or adjacent to, the flight-paths of aircraft landing at, or taking off from, the international airport of Kai Tak. The subjective responses of the Chinese correlate well with the Noise and Number Index. Comparisons of the responses of the Chinese group with those of teachers and firemen in the city and with Londoners have been attempted.     

Auditory brainstem responses to chirps delivered by different insert earphones

The frequency response and sensitivity of the ER-3A and ER-2 insert earphones are measured in the occluded-ear simulator using three ear canal extensions. Compared to the other two extensions, the DB 0370 (Bru?el & Kj?r), which is recommended by the international standards, introduces a significant resonance peak around 4500 Hz. The ER-3A has an amplitude response like a band-pass filter (1400 Hz, 6 dB/octave -4000 Hz, -36 dB/octave), and a group delay with "ripples" of up to ±0.5 ms, while the ER-2 has an amplitude response, and a group delay which are flat and smooth up to above 10000 Hz. Both earphones are used to record auditory brainstem responses, ABRs, from 22 normal-hearing ears in response to two chirps and a click at levels from 20 to 80 dB nHL. While the click-ABRs are slightly larger for ER-2 than for ER-3A, the chirp-ABRs are much larger for ER-2 than for ER-3A at levels below 60 dB nHL. With a simulated amplitude response of the ER-3A and the smooth group delay of the ER-2 it is shown that the increased chirp-ABR amplitude with the ER-2 is caused by its broader amplitude response and not by its smoother group delay.     

Rotation in an asymmetric multidimensional periodic potential due to colored noise

We analyze the motion of an overdamped classical particle in a multidimensional periodic potential, driven by an external noise. We demonstrate that in the steady state the presence of temporal correlations in the noise and spatial asymmetry within a period of the potential could lead to particle rotation. The rotation is a direct consequence of a change in the sign of the noise-induced drift motion in each dimension. By choosing different potentials, we can generate a variety of flow patterns from laminar drifts to rotations.     

Synchronization of periodic self-oscillations by common noise

We consider the effect of external noise on the stability properties of self-oscillations. A stochastic equation for the phase is derived at the limit of weak noise (in the appropriate sense). The stationary probability-density distribution is used for an analytic calculation of the Lyapunov exponent. We show that the exponent is always negative for the small noise level, which corresponds to synchronization of self-oscillations.     

Dynamics of oscillators with periodic dichotomous noise

The dynamics of bistable oscillators driven by periodic dichotomous noise is described. The stochastic differential equation governing the flow implies smooth trajectories between noise switching events. The dynamics of the two-branched map induced by this flow is a Markov process. Harmonic and quartic models of the bistable potential are studied in the overdamped limit. In the linear (harmonic) case the dynamics can be reduced to a stochastic one-dimensional map with two branches. The moments decay exponentially in this case, although the invariant measure may be multifractal. For strong damping, relaxation induces a cascade leading to a Cantor set and anomalous decay of the density in this case is modeled by a Markov chain. For the physically more realistic case of a quartic potential many additional features arise since the contraction factor is distance dependent. By tuning the barrier-height parameter in the quartic potential, noise-induced transition rates with the characteristics of intermittency are found.     

Critique of subjective responses of Chinese to aircraft noise

A recent paper has reported a difference in response to aircraft noise between the community living around Hong Kong International Airport and that living around Heathrow Airport in the UK. The difference has been ascribed to a different sensitivity of Chinese in Hong Kong to aircraft noise. This paper questions whether any such difference exists and suggests that the result is more likely a function of the techniques of survey and analysis adopted in the Hong Kong study. This is based on a statistical comparison of the regression lines and on an examination of the problems associated with transferring an annoyance scale developed in one environment to another.     

Magnetoencephalographic responses correspond to individual annoyance of bandpass noise

The relation between human brain responses to an individual's annoyance of bandpass noise was investigated using magnetoencephalography (MEG) measurements and analysis by autocorrelation function (ACF) and cross-correlation function (CCF). Pure tone and bandpass noises with a centre frequency of 1000 Hz were used as source signals. The sound pressure level was constant at 74 dBA and the duration of the stimulus was 2.0 s. The scale values of annoyance for each subject were obtained by paired-comparison tests. In MEG measurements, the combination of a reference stimulus (pure tone) and test stimuli (bandpass noise) was alternately presented 30 times at a constant 2 s interstimulus interval. The results show that the effective duration of the ACF, τ_e, of MEG in the 8-13 Hz range, which represent repetitive features within the signal itself, became shorter during the presentation of an annoying stimulus. Also, the maximum value of the CCF, |φ(τ)|_max, became smaller. The shorter τ_e and smaller |φ(τ)|_max indicate that a wider area of the brain is unstable for longer with annoying auditory stimuli.     

Auditory steady-state responses to chirp stimuli based on cochlear traveling wave delay

This study investigates the use of chirp stimuli to compensate for the cochlear traveling wave delay. The temporal dispersion in the cochlea is given by the traveling time, which in this study is estimated from latency-frequency functions obtained from (1) a cochlear model, (2) tone-burst auditory brain stem response (ABR) latencies, (3) and narrow-band ABR latencies. These latency-frequency functions are assumed to reflect the group delay of a linear system that modifies the phase spectrum of the applied stimulus. On the basis of this assumption, three chirps are constructed and evaluated in 49 normal-hearing subjects. The auditory steady-state responses to these chirps and to a click stimulus are compared at two levels of stimulation (30 and 50 dB nHL) and a rate of 90s. The chirps give shorter detection time and higher signal-to-noise ratio than the click. The shorter detection time obtained by the chirps is equivalent to an increase in stimulus level of 20 dB or more. The results indicate that a chirp is a more efficient stimulus than a click for the recording of early auditory evoked responses in normal-hearing adults using transient sounds at a high rate of stimulation.     

Auditory evoked responses: A tool to assess the fetal neurological activity

An intact auditory system at birth is requisite for the successful accomplishment of many developmental skills. Evoked responses to auditory stimuli have been used as a sensitive test to determine the functional status of the adult and neonatal brain. It has been established that fetuses can hear in utero and respond to external acoustic stimuli. We present an overview of the transmission of sound through the maternal abdomen to the fetal ear and the recordings of an auditory evoked response obtained from the fetus using a non-invasive magnetoencephalography technique. The investigation of cortical activity of the fetus in response to auditory stimulation can help understand and track the neurological development of the fetus.     

Absence of periodic solutions to scale invariant classical field theories

It is shown that in 3 + 1 Minkowski space classical field theories with energy-momentum θ_μν(x,t) satisfying θ₀₀(x,t) ? 0 and θ_μ^μ(x,t) = 0 have no finite energy periodic (or static) solutions. In particular this rules out classical glueball solutions. to Yang-Mills theories with compact gauge groups.     

Phase-sensitive noise in quantum dots under periodic perturbation

We evaluate the ensemble averaged noise in a chaotic quantum dot subject to dc bias and a periodic perturbation of frequency Omega. The noise displays cusps at bias V(n)=n variant Planck's over 2 pi Omega/e that survive the average, even when the period of the perturbation is far shorter than the dwell time in the dot. These features are sensitive to the phase of the time-dependent scattering amplitudes of electrons to pass through the system, and thus provide a novel signature of phase-coherent transport that persists into the nonadiabatic limit.     

Unstable periodic orbits and noise in chaos computing

Different methods to utilize the rich library of patterns and behaviors of a chaotic system have been proposed for doing computation or communication. Since a chaotic system is intrinsically unstable and its nearby orbits diverge exponentially from each other, special attention needs to be paid to the robustness against noise of chaos-based approaches to computation. In this paper unstable periodic orbits, which form the skeleton of any chaotic system, are employed to build a model for the chaotic system to measure the sensitivity of each orbit to noise, and to select the orbits whose symbolic representations are relatively robust against the existence of noise. Furthermore, since unstable periodic orbits are extractable from time series, periodic orbit-based models can be extracted from time series too. Chaos computing can be and has been implemented on different platforms, including biological systems. In biology noise is always present; as a result having a clear model for the effects of noise on any given biological implementation has profound importance. Also, since in biology it is hard to obtain exact dynamical equations of the system under study, the time series techniques we introduce here are of critical importance.     

Sex-related differences in vocal responses to pitch feedback perturbations during sustained vocalization

The present study assessed the effect of sex on voice fundamental frequency (F(0)) responses to pitch feedback perturbations during sustained vocalization. Sixty-four native-Mandarin speakers heard their voice pitch feedback shifted at ± 50, ± 100, or ± 200 cents for 200 ms, five times during each vocalization. The results showed that, as compared to female speakers, male speakers produced significantly larger but slower vocal responses to the pitch-shifted stimuli. These findings reveal a modulation of vocal response as a function of sex, and suggest that there may be a differential processing of vocal pitch feedback perturbations between men and women.     

Auditory nerve fiber responses to electric stimulation: modulated and unmodulated pulse trains

Many modern cochlear implants use sound processing strategies that stimulate the cochlea with modulated pulse trains. Rubinstein et al. [Hear. Res. 127, 108 (1999)] suggested that representation of the modulator in auditory nerve responses might be improved by the addition of a sustained, high-rate, desynchronizing pulse train (DPT). In addition, activity in response to the DPT may mimic the spontaneous activity (SA) in a healthy ear. The goals of this study were to compare responses of auditory nerve fibers in acutely deafened, anesthetized cats elicited by high-rate electric pulse trains delivered through an intracochlear electrode with SA, and to measure responses of these fibers to amplitude-modulated pulse trains superimposed upon a DPT. Responses to pulse trains showed variability from presentation to presentation, but differed from SA in the shape of the envelope of the interval histogram (IH) for pulse rates above 4.8 kpps (kilo pulses per second). These IHs had a prominent mode near 5 ms that was followed by a long tail. Responses to modulated biphasic pulse trains resembled responses to tones in intact ears for small (<10%) modulation depths, suggesting that acousticlike responses to sinusoidal stimuli might be obtained with a DPT. However, realistic responses were only observed over a narrow range of levels and modulation depths. Improved coding of complex stimulus waveforms may be achieved by signal processing strategies for cochlear implants that properly incorporate a DPT.     

Effect of background levels on community responses to aircraft noise

The effect of variations in background noise levels on community reactions to aircraft noise has been investigated by using questionnaire and sound level data collected at a stratified random sample of residential sites in the vicinity of Toronto International Airport. The effects of variations in background noise (24 hour L_eq) on both individual and aggregate responses to aircraft noise have been examined. The response variables considered include annoyance, activity interference and complaints. The results of various statistical analyses show that the effect of background level is generally not significant. These findings are consistent with relevant findings from previous laboratory studies, but not with those from previous field studies.