366 research outputs found
Speed and Accuracy of Static Image Discrimination by Rats
When discriminating dynamic noisy sensory signals, human and primate subjects
achieve higher accuracy when they take more time to decide, an effect
attributed to accumulation of evidence over time to overcome neural noise. We
measured the speed and accuracy of twelve freely behaving rats discriminating
static, high contrast photographs of real-world objects for water reward in a
self-paced task. Response latency was longer in correct trials compared to
error trials. Discrimination accuracy increased with response latency over the
range of 500-1200ms. We used morphs between previously learned images to vary
the image similarity parametrically, and thereby modulate task difficulty from
ceiling to chance. Over this range we find that rats take more time before
responding in trials with more similar stimuli. We conclude that rats'
perceptual decisions improve with time even in the absence of temporal
information in the stimulus, and that rats modulate speed in response to
discrimination difficulty to balance speed and accuracy
The effect of slip variability on earthquake slip-length scaling
There has been debate on whether average slip D in long ruptures should scale with rupture length L, or with rupture width W. This scaling discussion is equivalent to asking whether average stress drop Δσ, which is sometimes considered an intrinsic frictional property of a fault, is approximately constant over a wide range of earthquake sizes. In this paper, we examine slip-length scaling relations using a simplified 1-D model of spatially heterogeneous slip. The spatially heterogeneous slip is characterized by a stochastic function with a Fourier spectrum that decays as k^(−α), where k is the wavenumber and α is a parameter that describes the spatial smoothness of slip. We adopt the simple rule that an individual earthquake rupture consists of only one spatially continuous segment of slip (i.e. earthquakes are not generally separable into multiple disconnected segments of slip). In this model, the slip-length scaling relation is intimately related to the spatial heterogeneity of the slip; linear scaling of average slip with rupture length only occurs when α is about 1.5, which is a relatively smooth spatial distribution of slip. We investigate suites of simulated ruptures with different smoothness, and we show that faults with large slip heterogeneity tend to have higher D/L ratios than those with spatially smooth slip. The model also predicts that rougher faults tend to generate larger numbers of small earthquakes, whereas smooth faults may have a uniform size distribution of earthquakes. This simple 1-D fault model suggests that some aspects of stress drop scaling are a consequence of whatever is responsible for the spatial heterogeneity of slip in earthquakes
A Fluctuation-Driven Mechanism for Slow Decision Processes in Reverberant Networks
The spike activity of cells in some cortical areas has been found to be correlated with reaction times and behavioral responses during two-choice decision tasks. These experimental findings have motivated the study of biologically plausible winner-take-all network models, in which strong recurrent excitation and feedback inhibition allow the network to form a categorical choice upon stimulation. Choice formation corresponds in these models to the transition from the spontaneous state of the network to a state where neurons selective for one of the choices fire at a high rate and inhibit the activity of the other neurons. This transition has been traditionally induced by an increase in the external input that destabilizes the spontaneous state of the network and forces its relaxation to a decision state. Here we explore a different mechanism by which the system can undergo such transitions while keeping the spontaneous state stable, based on an escape induced by finite-size noise from the spontaneous state. This decision mechanism naturally arises for low stimulus strengths and leads to exponentially distributed decision times when the amount of noise in the system is small. Furthermore, we show using numerical simulations that mean decision times follow in this regime an exponential dependence on the amplitude of noise. The escape mechanism provides thus a dynamical basis for the wide range and variability of decision times observed experimentally
Nuclear dependence of the transverse single-spin asymmetry in the production of charged hadrons at forward rapidity in polarized , Al, and Au collisions at GeV
We report on the nuclear dependence of transverse single-spin asymmetries
(TSSAs) in the production of positively-charged hadrons in polarized
, Al and Au collisions at
GeV. The measurements have been performed at forward
rapidity () over the range of GeV and
. We observed a positive asymmetry for
positively-charged hadrons in \polpp collisions, and a significantly reduced
asymmetry in + collisions. These results reveal a nuclear
dependence of charged hadron in a regime where perturbative techniques
are relevant. These results provide new opportunities to use \polpA collisions
as a tool to investigate the rich phenomena behind TSSAs in hadronic collisions
and to use TSSA as a new handle in studying small-system collisions.Comment: 303 authors from 66 institutions, 9 pages, 2 figures, 1 table. v1 is
version accepted for publication in Physical Review Letters. Plain text data
tables for the points plotted in figures for this and previous PHENIX
publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Nuclear dependence of the transverse-single-spin asymmetry for forward neutron production in polarized collisions at GeV
During 2015 the Relativistic Heavy Ion Collider (RHIC) provided collisions of
transversely polarized protons with Au and Al nuclei for the first time,
enabling the exploration of transverse-single-spin asymmetries with heavy
nuclei. Large single-spin asymmetries in very forward neutron production have
been previously observed in transversely polarized collisions at
RHIC, and the existing theoretical framework that was successful in describing
the single-spin asymmetry in collisions predicts only a moderate
atomic-mass-number () dependence. In contrast, the asymmetries observed at
RHIC in collisions showed a surprisingly strong dependence in
inclusive forward neutron production. The observed asymmetry in Al
collisions is much smaller, while the asymmetry in Au collisions is a
factor of three larger in absolute value and of opposite sign. The interplay of
different neutron production mechanisms is discussed as a possible explanation
of the observed dependence.Comment: 315 authors, 8 pages, 4 figures, 1 table. v2 is version accepted for
publication in Phys. Rev. Lett. Plain text data tables for the points plotted
in figures for this and previous PHENIX publications are (or will be)
publicly available at http://www.phenix.bnl.gov/papers.htm
- …