1,176 research outputs found
Spatially valid proprioceptive cues improve the detection of a visual stimulus
Vision and proprioception are the main sensory modalities that convey hand location and direction of movement. Fusion of these sensory signals into a single robust percept is now well documented. However, it is not known whether these modalities also interact in the spatial allocation of attention, which has been demonstrated for other modality pairings. The aim of this study was to test whether proprioceptive signals can spatially cue a visual target to improve its detection. Participants were instructed to use a planar manipulandum in a forward reaching action and determine during this movement whether a near-threshold visual target appeared at either of two lateral positions. The target presentation was followed by a masking stimulus, which made its possible location unambiguous, but not its presence. Proprioceptive cues were given by applying a brief lateral force to the participantâs arm, either in the same direction (validly cued) or in the opposite direction (invalidly cued) to the on-screen location of the mask. The dⲠdetection rate of the target increased when the direction of proprioceptive stimulus was compatible with the location of the visual target compared to when it was incompatible. These results suggest that proprioception influences the allocation of attention in visual spac
A neural surveyor to map touch on the body
Perhaps the most recognizable sensory map in all of neuroscience is the somatosensory homunculus. Although it seems straightforward, this simple representation belies the complex link between an activation in a somatotopic map and the associated touch location on the body. Any isolated activation is spatially ambiguous without a neural decoder that can read its position within the entire map, but how this is computed by neural networks is unknown. We propose that the somatosensory system implements multilateration, a common computation used by surveying and global positioning systems to localize objects. Specifically, to decode touch location on the body, multilateration estimates the relative distance between the afferent input and the boundaries of a body part (e.g., the joints of a limb). We show that a simple feedforward neural network, which captures several fundamental receptive field properties of cortical somatosensory neurons, can implement a Bayes-optimal multilateral computation. Simulations demonstrated that this decoder produced a pattern of localization variability between two boundaries that was unique to multilateration. Finally, we identify this computational signature of multilateration in actual psychophysical experiments, suggesting that it is a candidate computational mechanism underlying tactile localization
Distances to Galactic high-velocity clouds. Complex C
We report the first determination of a distance bracket for the high-velocity
cloud (HVC) complex C. Combined with previous measurements showing that this
cloud has a metallicity of 0.15 times solar, these results provide ample
evidence that complex C traces the continuing accretion of intergalactic gas
falling onto the Milky Way. Accounting for both neutral and ionized hydrogen as
well as He, the distance bracket implies a mass of 3-14x10^6 M_sun, and the
complex represents a mass inflow of 0.1-0.25 M_sun/yr. We base our distance
bracket on the detection of CaII absorption in the spectrum of the blue
horizontal branch star SDSS J120404.78+623345.6, in combination with a
significant non-detection toward the BHB star BS 16034-0114. These results set
a strong distance bracket of 3.7-11.2 kpc on the distance to complex C. A more
weakly supported lower limit of 6.7 kpc may be derived from the spectrum of the
BHB star BS 16079-0017.Comment: Accepted for publication in ApJ Letter
The Origin of the Bifurcation in the Sagittarius Stream
The latest Sloan Digital Sky Survey data reveal a prominent bifurcation in
the distribution of debris of the Sagittarius dwarf spheroidal (Sgr) beginning
at a right ascension of roughly 190 degrees. Two branches of the stream (A and
B) persist at roughly the same heliocentric distance over at least 50 degrees
of arc. There is also evidence for a more distant structure (C) well behind the
A branch. This paper provides the first explanation for the bifurcation. It is
caused by the projection of the young leading (A) and old trailing (B) tidal
arms of the Sgr, whilst the old leading arm (C) lies well behind A. This
explanation is only possible if the halo is close to spherical, as the angular
difference between the branches is a measure of the precession of the orbital
plane.Comment: ApJ, in pres
The scaling relation of early-type galaxies in clusters. II: Spectroscopic data for galaxies in eight nearby clusters
AIMS: We present in this work low and intermediate resolution spectroscopic
data collected for 152 early type galaxies in 8 nearby clusters with z
0.10.
METHODS: We use low resolution data to produce the redshift and the
K-correction for every individual galaxy, as well as to give their overall
spectral energy distribution, and some spectral indicators, including the
4000\AA break, the Mg strength, and the NaD equivalent width.We have also
obtained higher resolution data for early type galaxies in three of the
clusters, to determine their central velocity dispersion.
RESULTS: The effect of the resolution on the measured parameters is
discussed.
CONCLUSIONS: New accurate systemic redshift and velocity dispersion is
presented for four of the surveyed clusters, A98, A3125, A3330, and DC2103-39.
We have found that the K-correction values for E/S0 bright galaxies in a given
nearby clusters are very similar. We also find that the distribution of the
line indicators significantly differ from cluster to cluster.Comment: 16 pages, 9 figures, Accepted in A&
Internal dynamics of the galaxy cluster Abell 545
Diffuse radio emission in galaxy clusters, and their connection with cluster
mergers, are still debated. We seek to explore the internal dynamics of the
radio halo cluster Abell 545. This cluster is also peculiar for hosting in its
center a very bright, red, diffuse intracluster light due to an old, stellar
population, so bright to be named as "star pile". Our analysis is based on
redshift data for 110 galaxies. We identify 95 cluster members and analyze the
cluster internal dynamics by combining galaxy velocities and positions. We also
use both photometric and X-ray data. We estimate the cluster redshift,
z=0.1580, a velocity dispersion of 1200 km/s, and ICM temperature kT_X~8 keV.
Our optical and X-ray analyses detect substructures. Optical data reveal three
main galaxy clumps (center, NNW, and NE), and possibly a fourth clump at South.
There is not a dominant galaxy and the four brightest galaxies avoid the
cluster core (>~0.4h distant from the cluster center) and are >~1500 km/s far
from the mean cluster velocity. The analysis of the X-ray surface brightness
distribution provides us evidence of a disturbed dynamical phase. Located in
the star pile region there is the brightest galaxies of the cluster core (CBCG)
and a very compact elliptical galaxy. We show that the star pile has a similar
redshift to that of the CBCG. Both the star pile and the CBCG are at rest in
the cluster rest frame. The emerging picture of Abell 545 is that of a massive,
M(R<1.6 h_70^-1 Mpc)=1.1-1.8x10^15 h_70^-1 Msun, very complex cluster with
merging occurring along two directions. A545 gives another proof in the favor
of the connection between cluster merger and extended, diffuse radio emission.
The star pile, likely due to the process of a brightest galaxy forming in the
cluster core. A545 represents a textbook cluster where to study the
simultaneous formation of a galaxy system and its brightest galaxy.Comment: 16 pages, 11 figures and 2 tables. Accepted in A&
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