44,460 research outputs found
Multisensory Integration Sites Identified by Perception of Spatial Wavelet Filtered Visual Speech Gesture Information
Perception of speech is improved when presentation of the audio signal is accompanied by concordant visual speech gesture information. This enhancement is most prevalent when the audio signal is degraded. One potential means by which the brain affords perceptual enhancement is thought to be through the integration of concordant information from multiple sensory channels in a common site of convergence, multisensory integration (MSI) sites. Some studies have identified potential sites in the superior temporal gyrus/sulcus (STG/S) that are responsive to multisensory information from the auditory speech signal and visual speech movement. One limitation of these studies is that they do not control for activity resulting from attentional modulation cued by such things as visual information signaling the onsets and offsets of the acoustic speech signal, as well as activity resulting from MSI of properties of the auditory speech signal with aspects of gross visual motion that are not specific to place of articulation information. This fMRI experiment uses spatial wavelet bandpass filtered Japanese sentences presented with background multispeaker audio noise to discern brain activity reflecting MSI induced by auditory and visual correspondence of place of articulation information that controls for activity resulting from the above-mentioned factors. The experiment consists of a low-frequency (LF) filtered condition containing gross visual motion of the lips, jaw, and head without specific place of articulation information, a midfrequency (MF) filtered condition containing place of articulation information, and an unfiltered (UF) condition. Sites of MSI selectively induced by auditory and visual correspondence of place of articulation information were determined by the presence of activity for both the MF and UF conditions relative to the LF condition. Based on these criteria, sites of MSI were found predominantly in the left middle temporal gyrus (MTG), and the left STG/S (including the auditory cortex). By controlling for additional factors that could also induce greater activity resulting from visual motion information, this study identifies potential MSI sites that we believe are involved with improved speech perception intelligibility
Multimode laser cooling and ultra-high sensitivity force sensing with nanowires
Photo-induced forces can be used to manipulate and cool the mechanical motion
of oscillators. When the oscillator is used as a force sensor, such as in
atomic force microscopy, active feedback is an enticing route to enhancing
measurement performance. Here, we show broadband multimode cooling of dB
down to a temperature of ~K in the stationary regime. Through the use
of periodic quiescence feedback cooling, we show improved signal-to-noise
ratios for the measurement of transient signals. We compare the performance of
real feedback to numerical post-processing of data and show that both methods
produce similar improvements to the signal-to-noise ratio of force
measurements. We achieved a room temperature force measurement sensitivity of
N with integration time of less than ms. The high
precision and fast force microscopy results presented will potentially benefit
applications in biosensing, molecular metrology, subsurface imaging and
accelerometry.Comment: 16 pages and 3 figures for the main text, 14 pages and 5 figures for
the supplementary informatio
Cavity-Enhanced Ultrafast Transient Absorption Spectroscopy
We present a new technique using a frequency comb laser and optical cavities
for performing ultrafast transient absorption spectroscopy with improved
sensitivity. Resonantly enhancing the probe pulses, we demonstrate a
sensitivity of OD = 1 \times 10^{-9}/\sqrt{\mbox{Hz}} for averaging
times as long as 30 s per delay point (OD).
Resonantly enhancing the pump pulses allows us to produce a high excitation
fraction at high repetition-rate, so that signals can be recorded from samples
with optical densities as low as OD , or column densities molecules/cm. This high sensitivity enables new directions for
ultrafast spectroscopy
Correlation between amygdala BOLD activity and frontal EEG asymmetry during real-time fMRI neurofeedback training in patients with depression
Real-time fMRI neurofeedback (rtfMRI-nf) is an emerging approach for studies
and novel treatments of major depressive disorder (MDD). EEG performed
simultaneously with an rtfMRI-nf procedure allows an independent evaluation of
rtfMRI-nf brain modulation effects. Frontal EEG asymmetry in the alpha band is
a widely used measure of emotion and motivation that shows profound changes in
depression. However, it has never been directly related to simultaneously
acquired fMRI data. We report the first study investigating
electrophysiological correlates of the rtfMRI-nf procedure, by combining
rtfMRI-nf with simultaneous and passive EEG recordings. In this pilot study,
MDD patients in the experimental group (n=13) learned to upregulate BOLD
activity of the left amygdala using an rtfMRI-nf during a happy emotion
induction task. MDD patients in the control group (n=11) were provided with a
sham rtfMRI-nf. Correlations between frontal EEG asymmetry in the upper alpha
band and BOLD activity across the brain were examined. Average individual
changes in frontal EEG asymmetry during the rtfMRI-nf task for the experimental
group showed a significant positive correlation with the MDD patients'
depression severity ratings, consistent with an inverse correlation between the
depression severity and frontal EEG asymmetry at rest. Temporal correlations
between frontal EEG asymmetry and BOLD activity were significantly enhanced,
during the rtfMRI-nf task, for the amygdala and many regions associated with
emotion regulation. Our findings demonstrate an important link between amygdala
BOLD activity and frontal EEG asymmetry. Our EEG asymmetry results suggest that
the rtfMRI-nf training targeting the amygdala is beneficial to MDD patients,
and that alpha-asymmetry EEG-nf would be compatible with the amygdala
rtfMRI-nf. Combination of the two could enhance emotion regulation training and
benefit MDD patients.Comment: 28 pages, 16 figures, to appear in NeuroImage: Clinica
Minimum requirements for feedback enhanced force sensing
The problem of estimating an unknown force driving a linear oscillator is
revisited. When using linear measurement, feedback is often cited as a
mechanism to enhance bandwidth or sensitivity. We show that as long as the
oscillator dynamics are known, there exists a real-time estimation strategy
that reproduces the same measurement record as any arbitrary feedback protocol.
Consequently some form of nonlinearity is required to gain any advantage beyond
estimation alone. This result holds true in both quantum and classical systems,
with non-stationary forces and feedback, and in the general case of
non-Gaussian and correlated noise. Recently, feedback enhanced incoherent force
sensing has been demonstrated [Nat. Nano. \textbf{7}, 509 (2012)], with the
enhancement attributed to a feedback induced modification of the mechanical
susceptibility. As a proof-of-principle we experimentally reproduce this result
through straightforward filtering.Comment: 5 pages + 2 pages of Supplementary Informatio
S-cone signals invisible to the motion system can improve motion extraction via grouping by color
Peer reviewedPublisher PD
Fighting against fast speckle decorrelation for light focusing inside live tissue by photon frequency shifting
Light focusing inside live tissue by digital optical phase conjugation (DOPC) has drawn increasing interest due to its potential biomedical applications in optogenetics, microsurgery, phototherapy, and deep-tissue imaging. However, fast physiological motions in a live animal, including blood flow and respiratory motions, produce undesired photon perturbation and thus inevitably deteriorate the performance of light focusing. Here, we develop a photon-frequency-shifting DOPC method to fight against fast physiological motions by switching the states of a guide star at a distinctive frequency. Therefore, the photons tagged by the guide star are well detected at the specific frequency, separating them from the photons perturbed by fast motions. Light focusing was demonstrated in both phantoms in vitro and mice in vivo with substantially improved focusing contrast. This work puts a new perspective on light focusing inside live tissue and promises wide biomedical applications
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