832 research outputs found
Elaboration of a model of Pavlovian learning and performance: HeiDI
The model elaborated here adapts the influential pooled error term, first described by Allan R. Wagner and his colleague Robert A. Rescorla, to govern the formation of reciprocal associations between any pair of stimuli that are presented on a given trial. In the context of Pavlovian conditioning, these stimuli include various conditioned and unconditioned stimuli. This elaboration enables the model to deal with cue competition phenomena, including the relative validity effect, and evidence implicating separate error terms and attentional processes in association formation. The model also includes a performance rule, which provides a natural basis for (individual) variation in the strength and nature of conditioned behaviors that are observed in Pavlovian conditioning procedures. The new model thereby begins to address theoretical and empirical issues that were apparent when the Rescorla-Wagner model was first described, together with research inspired by the model over ensuing 50 years
Individual differences in the nature of conditioned behavior across a conditioned stimulus: adaptation and application of a model
Pavlovian conditioning procedures produce marked individual differences in the form of conditioned behavior. For example, when rats are given conditioning trials in which the temporary insertion of a lever into an operant chamber (the conditioned stimulus, CS) is paired with the delivery of food (the unconditioned stimulus, US), they exhibit knowledge of the leverfood relationship in different ways. For some rats (known as sign-trackers) interactions with the lever dominate, while for others (goal-trackers) approaching the food well dominates. A formal model of Pavlovian conditioning (HeiDI) attributes such individual differences in behavior to variations in the perceived salience of the CS and US. An application of the model in which the perceived salience of the CS declines (i.e., adapts) across its duration, predicts changes in these individual differences within the presentation of the CS: The sign-tracking bias is predicted to decline and goal-tracking bias is predicted to increase across the presentation of a lever. The accuracy of these predictions was confirmed though analysis of archival data from female and male rats
The nature of phenotypic variation in Pavlovian conditioning
Pavlovian conditioning procedures result in dramatic individual differences in the topography of learnt behaviors in rats: When the temporary insertion of a lever into an operant chamber is paired with food pellets, some rats (known as sign-trackers) predominantly interact with the lever, while others (known as goal-trackers) predominantly approach the food well. Two experiments examined the sensitivity of these two behaviors to changing reinforcement contingencies in groups of males and female rats exhibiting the different phenotypes (i.e., sign-trackers and goal-trackers). In both phenotypes, behavior oriented to the food well was more sensitive to contingency changes (e.g., a reversal in which of two levers was reinforced) than was lever-oriented behavior. That is, the nature of the two behaviors differed independently of the rats in which they were manifest. These results indicate that the behavioral phenotypes reflect the parallel operation of a stimulus-stimulus associative process that gives rise to food-well activity and a stimulus-response process that gives rise to leveroriented activity, rather than the operation of a single process (e.g., stimulus-stimulus) that generates both behaviors
VIP: An Experiment to Search for a Violation of the Pauli Exclusion Principle
The Pauli Exclusion Principle is a basic principle of Quantum Mechanics, and
its validity has never been seriously challenged. However, given its
fundamental standing, it is very important to check it as thoroughly as
possible. Here we describe the VIP (VIolation of the Pauli exclusion principle)
experiment, an improved version of the Ramberg and Snow experiment (E. Ramberg
and G. Snow, {\it Phys. Lett. B} {\bf 238}, 438 (1990)); VIP has just completed
the installation at the Gran Sasso underground laboratory, and aims to test the
Pauli Exclusion Principle for electrons with unprecedented accuracy, down to
. We report preliminary experimental
results and briefly discuss some of the implications of a possible violation.Comment: Plenary talk presented by E. Milotti at Meson 2006, Cracow, 9-13 June
200
New experimental limit on the Pauli Exclusion Principle violation by electrons
The Pauli Exclusion Principle (PEP) is one of the basic principles of modern
physics and, even if there are no compelling reasons to doubt its validity, it
is still debated today because an intuitive, elementary explanation is still
missing, and because of its unique stand among the basic symmetries of physics.
The present paper reports a new limit on the probability that PEP is violated
by electrons, in a search for a shifted K line in copper: the presence
of this line in the soft X-ray copper fluorescence would signal a transition to
a ground state already occupied by 2 electrons. The obtained value, , improves the existing limit by almost two
orders of magnitude.Comment: submitted to Phys. Lett.
The VIP Experiment
The Pauli Exclusion Principle (PEP) is a basic principle of Quantum
Mechanics, and its validity has never been seriously challenged. However, given
its importance, it is very important to check it as thoroughly as possible.
Here we describe the VIP (Violation of PEP) experiment, an improved version of
the Ramberg and Snow experiment (Ramberg and Snow, Phys. Lett. B238 (1990)
438); VIP shall be performed at the Gran Sasso underground laboratories, and
aims to test the Pauli Exclusion Principle for electrons with unprecedented
accuracy, down to Comment: 7 pages, 5 figures, PDF only, presented by Edoardo Milotti to the
conference "Quantum Theory: reconsideration of foundations-3", Vaxjo
(Sweden), June, 6-11 200
New experimental limit on Pauli Exclusion Principle violation by electrons (the VIP experiment)
The Pauli Exclusion Principle is one of the basic principles of modern
physics and is at the very basis of our understanding of matter: thus it is
fundamental importance to test the limits of its validity. Here we present the
VIP (Violation of the Pauli Exclusion Principle) experiment, where we search
for anomalous X-rays emitted by copper atoms in a conductor: any detection of
these anomalous X-rays would mark a Pauli-forbidden transition. ] VIP is
currently taking data at the Gran Sasso underground laboratories, and its
scientific goal is to improve by at least four orders of magnitude the previous
limit on the probability of Pauli violating transitions, bringing it into the
10**-29 - 10**-30 region. First experimental results, together with future
plans, are presented.Comment: To appear in proceedings of the XLVI International Winter Meeting on
Nuclear Physics, Bormio, Italy, January 20-26, 200
First measurements at the DAΦNE φ-factory with the DEAR experimental setup
The relevant background for the DEAR experiment } low-energy X rays and ionizing particles } present in the DEAR interaction region of the DA'NE e'e~ collider was investigated using the "rst-stage DEAR setup and CCD detectors. An extensive Monte Carlo simulation was performed for the present setup and beam conditions. Good quantitative agreement between measurements and simulation was achieved. This is a con"rmation that, with respect to the expected background, which gives an important contribution to the statistical precision of the experiment, the con"guration chosen to measure the strong interaction shift and width in kaonic hydrogen and kaonic deuterium can indeed reach the planned level of accuracy. ( 2000 Elsevier Science B.V. All rights reserved
Shedding New Light on Kaon-Nucleon/Nuclei Interaction and Its Astrophysical Implications with the AMADEUS Experiment at DAFNE
The AMADEUS experiment deals with the investigation of the low-energy
kaon-nuclei hadronic interaction at the DA{\Phi}NE collider at LNF-INFN, which
is fundamental to respond longstanding questions in the non-perturbative QCD
strangeness sector. The antikaon-nucleon potential is investigated searching
for signals from possible bound kaonic clusters, which would open the
possibility for the formation of cold dense baryonic matter. The confirmation
of this scenario may imply a fundamental role of strangeness in astrophysics.
AMADEUS step 0 consisted in the reanalysis of 2004/2005 KLOE dataset,
exploiting K- absorptions in H, 4He, 9Be and 12C in the setup materials. In
this paper, together with a review on the multi-nucleon K- absorption and the
particle identification procedure, the first results on the {\Sigma}0-p channel
will be presented including a statistical analysis on the possible accomodation
of a deeply bound stateComment: 6 pages, 2 figure, 1 table, HADRON 2015 conferenc
Testing the Pauli Exclusion Principle for Electrons
One of the fundamental rules of nature and a pillar in the foundation of
quantum theory and thus of modern physics is represented by the Pauli Exclusion
Principle. We know that this principle is extremely well fulfilled due to many
observations. Numerous experiments were performed to search for tiny violation
of this rule in various systems. The experiment VIP at the Gran Sasso
underground laboratory is searching for possible small violations of the Pauli
Exclusion Principle for electrons leading to forbidden X-ray transitions in
copper atoms. VIP is aiming at a test of the Pauli Exclusion Principle for
electrons with high accuracy, down to the level of 10 - 10,
thus improving the previous limit by 3-4 orders of magnitude. The experimental
method, results obtained so far and new developments within VIP2 (follow-up
experiment at Gran Sasso, in preparation) to further increase the precision by
2 orders of magnitude will be presented.Comment: Proceedings DISCRETE 2012-Third Symposium on Prospects in the Physics
of Discrete Symmetries, Lisbon, December 3-7, 201
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