33 research outputs found
Neural Encoding and Decoding with Deep Learning for Natural Vision
The overarching objective of this work is to bridge neuroscience and artificial intelligence to ultimately build machines that learn, act, and think like humans. In the context of vision, the brain enables humans to readily make sense of the visual world, e.g. recognizing visual objects. Developing human-like machines requires understanding the working principles underlying the human vision. In this dissertation, I ask how the brain encodes and represents dynamic visual information from the outside world, whether brain activity can be directly decoded to reconstruct and categorize what a person is seeing, and whether neuroscience theory can be applied to artificial models to advance computer vision. To address these questions, I used deep neural networks (DNN) to establish encoding and decoding models for describing the relationships between the brain and the visual stimuli. Using the DNN, the encoding models were able to predict the functional magnetic resonance imaging (fMRI) responses throughout the visual cortex given video stimuli; the decoding models were able to reconstruct and categorize the visual stimuli based on fMRI activity. To further advance the DNN model, I have implemented a new bidirectional and recurrent neural network based on the predictive coding theory. As a theory in neuroscience, predictive coding explains the interaction among feedforward, feedback, and recurrent connections. The results showed that this brain-inspired model significantly outperforms feedforward-only DNNs in object recognition. These studies have positive impact on understanding the neural computations under human vision and improving computer vision with the knowledge from neuroscience
The Application of Continuous Wavelet Transform Based Foreground Subtraction Method in 21 cm Sky Surveys
We propose a continuous wavelet transform based non-parametric foreground
subtraction method for the detection of redshifted 21 cm signal from the epoch
of reionization. This method works based on the assumption that the foreground
spectra are smooth in frequency domain, while the 21 cm signal spectrum is full
of saw-tooth-like structures, thus their characteristic scales are
significantly different. We can distinguish them in the wavelet coefficient
space easily and perform the foreground subtraction. Compared with the
traditional spectral fitting based method, our method is more tolerant to
complex foregrounds. Furthermore, we also find that when the instrument has
uncorrected response error, our method can also work significantly better than
the spectral fitting based method. Our method can obtain similar results with
the Wp smoothing method, which is also a non-parametric method, but our method
consumes much less computing time.Comment: Accepted by Ap
Precessing Binary Black Holes as Better Dark Sirens
Gravitational waves (GWs) from binary black hole mergers provide unique
opportunities for cosmological inference such as standard sirens. However, the
accurate determination of the luminosity distance of the event is limited by
the correlation between the distance and the angle between the binary's orbital
angular momentum and the observer's line of sight. In the letter, we
investigate the effect of precession on the distance estimation of binary black
hole events for the third-generation (3G) GW detectors. We find that the
precession can enhance the precision of distance inference by one order of
magnitude compared to the scenario where precession is absent. The constraint
on the host galaxies can be improved due to the improved distance measurement,
therefore the Hubble constant can be measured with higher precision and
accuracy. These findings underscore the noteworthy impact of precession on the
precision of distance estimation for 3G ground-based GW detectors, which can
serve as highly accurate probes of the Universe.Comment: 6 pages, 6 figure
Galaxy Infall by Interacting with its Environment: a Comprehensive Study of 340 Galaxy Clusters
To study systematically the evolution on the angular extents of the galaxy,
ICM, and dark matter components in galaxy clusters, we compiled the optical and
X-ray properties of a sample of 340 clusters with redshifts , based on
all the available data with the Sloan Digital Sky Survey (SDSS) and {\it
Chandra}/{\it XMM-Newton}. For each cluster, the member galaxies were
determined primarily with photometric redshift measurements. The radial ICM
mass distribution, as well as the total gravitational mass distribution, were
derived from a spatially-resolved spectral analysis of the X-ray data. When
normalizing the radial profile of galaxy number to that of the ICM mass, the
relative curve was found to depend significantly on the cluster redshift; it
drops more steeply towards outside in lower redshift subsamples. The same
evolution is found in the galaxy-to-total mass profile, while the ICM-to-total
mass profile varies in an opposite way. We interpret that the galaxies, the
ICM, and the dark matter components had similar angular distributions when a
cluster was formed, while the galaxies travelling interior of the cluster have
continuously fallen towards the center relative to the other components, and
the ICM has slightly expanded relative to the dark matter although it suffers
strong radiative loss. This cosmological galaxy infall, accompanied by an ICM
expansion, can be explained by considering that the galaxies interact strongly
with the ICM while they are moving through it. The interaction is considered to
create a large energy flow of erg per cluster from
the member galaxies to their environment, which is expected to continue over
cosmological time scales.Comment: 55 pages, 22 figures, accepted for publication in Astrophysical
Journa
Task-evoked functional connectivity does not explain functional connectivity differences between rest and task conditions
During complex tasks, patterns of functional connectivity differ from those in the resting state. However, what accounts for such differences remains unclear. Brain activity during a task reflects an unknown mixture of spontaneous and task-evoked activities. The difference in functional connectivity between a task state and the resting state may reflect not only task-evoked functional connectivity, but also changes in spontaneously emerging networks. Here, we characterized the differences in apparent functional connectivity between the resting state and when human subjects were watching a naturalistic movie. Such differences were marginally explained by the task-evoked functional connectivity involved in processing the movie content. Instead, they were mostly attributable to changes in spontaneous networks driven by ongoing activity during the task. The execution of the task reduced the correlations in ongoing activity among different cortical networks, especially between the visual and non-visual sensory or motor cortices. Our results suggest that task-evoked activity is not independent from spontaneous activity, and that engaging in a task may suppress spontaneous activity and its inter-regional correlation
Neuroprotective effect of arctigenin via upregulation of P-CREB in mouse primary neurons and human SH-SY5Y neuroblastoma cells.
Arctigenin (Arc) has been shown to act on scopolamine-induced memory deficit mice and to provide a neuroprotective effect on cultured cortical neurons from glutamate-induced neurodegeneration through mechanisms not completely defined. Here, we investigated the neuroprotective effect of Arc on H89-induced cell damage and its potential mechanisms in mouse cortical neurons and human SH-SY5Y neuroblastoma cells. We found that Arc prevented cell viability loss induced by H89 in human SH-SY5Y cells. Moreover, Arc reduced intracellular beta amyloid (Aβ) production induced by H89 in neurons and human SH-SY5Y cells, and Arc also inhibited the presenilin 1(PS1) protein level in neurons. In addition, neural apoptosis in both types of cells, inhibition of neurite outgrowth in human SH-SY5Y cells and reduction of synaptic marker synaptophysin (SYN) expression in neurons were also observed after H89 exposure. All these effects induced by H89 were markedly reversed by Arc treatment. Arc also significantly attenuated downregulation of the phosphorylation of CREB (p-CREB) induced by H89, which may contribute to the neuroprotective effects of Arc. These results demonstrated that Arc exerted the ability to protect neurons and SH-SY5Y cells against H89-induced cell injury via upregulation of p-CREB
The Physical Properties of Star-Forming Galaxies with Strong [O III] Lines at z=3.25
We present an analysis of physical properties of 34 [O III] emission-line
galaxies (ELGs) at z=3.2540.029 in the Extended Chandra Deep Field South
(ECDFS). These ELGs are selected from deep narrow H2S(1) and broad Ks imaging
of 383 arcmin obtained with CFHT/WIRCam. We construct spectral energy
distributions (SEDs) from U to Ks to derive the physical properties of ELGs.
These [O III] ELGs are identified as starburst galaxies with strong [O III]
lines of L([O III]) ~ 10 - 10 erg s, and have stellar
masses of M* ~ 10-10 M and star formation rates of ~
10-210 M yr. Our results show that 24% of our sample galaxies
are dusty with Av > 1 mag and EW(OIII) ~ 70-500 , which are often
missed in optically selected [O III] ELG samples. Their rest-frame UV and
optical morphologies from HST/ACS and HST/WFC3 deep imaging reveal that these
[O III] ELGs are mostly multiple-component systems (likely mergers) or compact.
And 20% of them are nearly invisible in the rest-frame UV owing to heavy dust
attenuation. Interestingly, we find that our samples reside in an overdensity
consisting of two components: one southeast (SE) with an overdensity factor of
~ 41 over a volume of 13 cMpc and the other
northwest (NW) with ~ 38 over a volume of 10 cMpc.
The two overdense substructures are expected to be virialized at z=0 with a
total mass of ~ 1.1 x 10 M and ~ 4.8 x 10 M, and
probably merge into a Coma-like galaxy cluster.Comment: 22 pages, 11 figures, 3 tables. Accepted for publication in Ap