2,018 research outputs found
Prioritized Sweeping Neural DynaQ with Multiple Predecessors, and Hippocampal Replays
During sleep and awake rest, the hippocampus replays sequences of place cells
that have been activated during prior experiences. These have been interpreted
as a memory consolidation process, but recent results suggest a possible
interpretation in terms of reinforcement learning. The Dyna reinforcement
learning algorithms use off-line replays to improve learning. Under limited
replay budget, a prioritized sweeping approach, which requires a model of the
transitions to the predecessors, can be used to improve performance. We
investigate whether such algorithms can explain the experimentally observed
replays. We propose a neural network version of prioritized sweeping
Q-learning, for which we developed a growing multiple expert algorithm, able to
cope with multiple predecessors. The resulting architecture is able to improve
the learning of simulated agents confronted to a navigation task. We predict
that, in animals, learning the world model should occur during rest periods,
and that the corresponding replays should be shuffled.Comment: Living Machines 2018 (Paris, France
Dynamical model of sequential spatial memory: winnerless competition of patterns
We introduce a new biologically-motivated model of sequential spatial memory
which is based on the principle of winnerless competition (WLC). We implement
this mechanism in a two-layer neural network structure and present the learning
dynamics which leads to the formation of a WLC network. After learning, the
system is capable of associative retrieval of pre-recorded sequences of spatial
patterns.Comment: 4 pages, submitted to PR
Why are Prices Sticky? Evidence from Business Survey Data
This paper offers new insights on the price setting behaviour of German retail firms using a novel dataset that
consists of a large panel of monthly business surveys from 1991-2006. The firm-level data allows matching changes
in firms' prices to several other firm-characteristics. Moreover, information on price expectations allow analyzing
the determinants of price updating. Using univariate and bivariate ordered probit specifications, empirical menu
cost models are estimated relating the probability of price adjustment and price updating, respectively, to both
time- and state- dependent variables. First, results suggest an important role for state-dependence; changes in
the macroeconomic and institutional environment as well as firm-specific factors are significantly related to the
timing of price adjustment. These findings imply that price setting models should endogenize the timing of price
adjustment in order to generate realistic predictions concerning the transmission of monetary policy. Second, an
analysis of price expectations yields similar results providing evidence in favour of state-dependent sticky plan
models. Third, intermediate input cost changes are among the most important determinants of price adjustment
suggesting that pricing models should explicitly incorporate price setting at different production stages. However, the results show that adjustment to input cost changes takes time indicating "additional stickiness" at the last stage of processing
The impact of sound field systems on learning and attention in elementary school classrooms
Purpose: An evaluation of the installation and use of sound field systems (SFS) was carried out to investigate their impact on teaching and learning in elementary school classrooms. Methods: The evaluation included acoustic surveys of classrooms, questionnaire surveys of students and teachers and experimental testing of students with and without the use of SFS. Students ’ perceptions of classroom environments and objective data evaluating change in performance on cognitive and academic assessments with amplification over a six month period are reported. Results: Teachers were positive about the use of SFS in improving children’s listening and attention to verbal instructions. Over time students in amplified classrooms did not differ from those in nonamplified classrooms in their reports of listening conditions, nor did their performance differ in measures of numeracy, reading or spelling. Use of SFS in the classrooms resulted in significantly larger gains in performance in the number of correct items on the nonverbal measure of speed of processing and the measure of listening comprehension. Analysis controlling for classroom acoustics indicated that students ’ listening comprehension score
Elemental spatial and temporal association formation in left temporal lobe epilepsy
The mesial temporal lobe (MTL) is typically understood as a memory structure in clinical settings, with the sine qua non of MTL damage in epilepsy being memory impairment. Recent models, however, understand memory as one of a number of higher cognitive functions that recruit the MTL through their reliance on more fundamental processes, such as “self-projection” or “association formation”. We examined how damage to the left MTL influences these fundamental processes through the encoding of elemental spatial and temporal associations. We used a novel fMRI task to image the encoding of simple visual stimuli, either rich or impoverished, in spatial or spatial plus temporal information. Participants included 14 typical adults (36.4 years, sd. 10.5 years) and 14 patients with left mesial temporal lobe damage as evidenced by a clinical diagnosis of left temporal lobe epilepsy (TLE) and left MTL impairment on imaging (34.3 years, sd. 6.6 years). In-scanner behavioral performance was equivalent across groups. In the typical group whole-brain analysis revealed highly significant bilateral parahippocampal activation (right > left) during spatial associative processing and left hippocampal/parahippocampal deactivation in joint spatial-temporal associative processing. In the left TLE group identical analyses indicated patients used MTL structures contralateral to the seizure focus differently and relied on extra-MTL regions to a greater extent. These results are consistent with the notion that epileptogenic MTL damage is followed by reorganization of networks underlying elemental associative processes. In addition, they provide further evidence that task-related fMRI deactivation can meaningfully index brain function. The implications of these findings for clinical and cognitive neuropsychological models of MTL function in TLE are discussed
Forgetting, Reminding, and Remembering: The Retrieval of Lost Spatial Memory
Retrograde amnesia can occur after brain damage because this disrupts sites of storage, interrupts memory consolidation, or interferes with memory retrieval. While the retrieval failure account has been considered in several animal studies, recent work has focused mainly on memory consolidation, and the neural mechanisms responsible for reactivating memory from stored traces remain poorly understood. We now describe a new retrieval phenomenon in which rats' memory for a spatial location in a watermaze was first weakened by partial lesions of the hippocampus to a level at which it could not be detected. The animals were then reminded by the provision of incomplete and potentially misleading information—an escape platform in a novel location. Paradoxically, both incorrect and correct place information reactivated dormant memory traces equally, such that the previously trained spatial memory was now expressed. It was also established that the reminding procedure could not itself generate new learning in either the original environment, or in a new training situation. The key finding is the development of a protocol that definitively distinguishes reminding from new place learning and thereby reveals that a failure of memory during watermaze testing can arise, at least in part, from a disruption of memory retrieval
Photography, Politics and Childhood: Exploring children’s multimodal relations with the public sphere
In qualitative research with children visually oriented and multimodal approaches are identified in the literature as more appropriate for approaching children’s meanings and feelings often deemed to lie beyond the realm of language. In our own research, a comparative ethnography which enquired into the relationships between childhood and public life, with six-to-eight year olds in three cities (Athens, Hyderabad and London), we have reflexively experimented with the employment and remixing of methodologies which would allow us to explore such relationships. In the process of our research, incorporating different visual and ethnographic methods, we have developed a data collection and production process, an adaptation of the photo-story, which allows for a multimodal, processual and reflective enquiry into children’s relationships of concern and politics of care. We review the central visual methods in research with children, we then proceed to provide a documentation of the method, its development and its rationale. Consequently, we provide some examples of the photostory method’s implementation in the Connectors Study together with a discussion of the production processes of the photo-stories themselves and our readings of them. We conclude with a section with reflections on the method, which, we argue provides a departure point from which we may rethink the political in childhood, as well as the ways in which photography is employed as a research method in the social sciences
A Study of Time-Dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the Upsilon(4S)
We present a measurement of time-dependent CP-violating asymmetries in
neutral B meson decays collected with the BABAR detector at the PEP-II
asymmetric-energy B Factory at the Stanford Linear Accelerator Center. The data
sample consists of 29.7 recorded at the
resonance and 3.9 off-resonance. One of the neutral B mesons,
which are produced in pairs at the , is fully reconstructed in
the CP decay modes , , , () and , or in flavor-eigenstate
modes involving and (). The flavor of the other neutral B meson is tagged at the time of
its decay, mainly with the charge of identified leptons and kaons. The proper
time elapsed between the decays is determined by measuring the distance between
the decay vertices. A maximum-likelihood fit to this flavor eigenstate sample
finds . The value of the asymmetry amplitude is determined from
a simultaneous maximum-likelihood fit to the time-difference distribution of
the flavor-eigenstate sample and about 642 tagged decays in the
CP-eigenstate modes. We find , demonstrating that CP violation exists in the neutral B meson
system. (abridged)Comment: 58 pages, 35 figures, submitted to Physical Review
Measurement of the Branching Fraction for B- --> D0 K*-
We present a measurement of the branching fraction for the decay B- --> D0
K*- using a sample of approximately 86 million BBbar pairs collected by the
BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is
detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the
K*- through its decay to K0S pi-. We measure the branching fraction to be
B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}.Comment: 7 pages, 1 postscript figure, submitted to Phys. Rev. D (Rapid
Communications
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