530 research outputs found
The hippocampus reevaluated in unconscious learning and memory: at a tipping point?
Classic findings from the neuropsychological literature invariably indicated that performances on tests of memory that can be accomplished without conscious awareness were largely spared in amnesia, while those that required conscious retrieval (e.g., via recognition or recall) of information learned in the very same sessions was devastatingly impaired. Based on reports of such dissociations, it was proposed that one of the fundamental distinctions between memory systems is whether or not they support conscious access to remembered content. Only recently have we come to realize that the putative systemic division of labor between conscious and unconscious memory is not so clean. A primary goal of this review is to examine recent evidence that has been advanced against the view that the hippocampus is selectively critical for conscious memory. Along the way, consideration is given to criticisms that have been levied against these findings, potential explanations for differences in the reported results are proposed, and methodological pitfalls in investigations of unconscious memory are discussed. Ultimately, it is concluded that a tipping point has been reached, and that while conscious recollection depends critically on hippocampal integrity, the reach of the hippocampus extends to unconscious aspects of memory performance when relational memory processing and representation are required
Impact of schizophrenia on anterior and posterior hippocampus during memory for complex scenes.
ObjectivesHippocampal dysfunction has been proposed as a mechanism for memory deficits in schizophrenia. Available evidence suggests that the anterior and posterior hippocampus could be differentially affected. Accordingly, we used fMRI to test the hypothesis that activity in posterior hippocampus is disproportionately reduced in schizophrenia, particularly during spatial memory retrieval.Methods26 healthy participants and 24 patients with schizophrenia from the UC Davis Early Psychosis Program were studied while fMRI was acquired on a 3 Tesla Siemens scanner. During encoding, participants were oriented to critical items through questions about item features (e.g., "Does the lamp have a square shade?") or spatial location (e.g., "Is the lamp on the table next to the couch?"). At test, participants determined whether scenes were changed or unchanged. fMRI analyses contrasted activation in a priori regions of interest (ROI) in anterior and posterior hippocampus during correct recognition of item changes and spatial changes.ResultsAs predicted, patients with schizophrenia exhibited reduced activation in the posterior hippocampus during detection of spatial changes but not during detection of item changes. Unexpectedly, patients exhibited increased activation of anterior hippocampus during detection of item changes. Whole brain analyses revealed reduced fronto-parietal and striatal activation in patients for spatial but not for item change trials.ConclusionsResults suggest a gradient of hippocampal dysfunction in which posterior hippocampus - which is necessary for processing fine-grained spatial relationships - is underactive, and anterior hippocampus - which may process context more globally - is overactive
Assessment of the effects of genetically modified potatoes on the structure and functioning of soil fungal communities
This thesis investigates the effects of genetic modification of the starch quality in potato on the structure and function of the soil fungal community via changes in root-exudates and litter composition, and compares the observed differences between the GM- and its parental variety in the context of the __normal__ variation effected by conventionally produced cultivars. In order to study the fungal community composition and functionality, an integrated approach of molecular fingerprinting methods and measurements of fungal enzymes involved in degradation of organic matter in the soil was employed. In field experiments the effect of soil type, season and plant growth stage on rhizosphere fungi were evaluated and in the greenhouse experiments stable isotopes were employed to monitor carbon flow from the plant to rhizosphere microbes and a decomposer experiment was designed to investigate the faith of the potatoes and leaves possibly left into the soil. The detailed greenhouse studies revealed differences between GM- and its parental variety. The field studies, however, confirmed that these differences are transient in field conditions and that fungi in the potato rhizosphere are affected more by soil type, sampling year, plant growth stage and cultivar type than the genetic modification.LEI Universiteit LeidenPlantenecologi
Facets of Distribution Identities in Probabilistic Team Semantics
We study probabilistic team semantics which is a semantical framework allowing the study of logical and probabilistic dependencies simultaneously. We examine and classify the expressive power of logical formalisms arising by different probabilistic atoms such as conditional independence and different variants of marginal distribution equivalences. We also relate the framework to the first-order theory of the reals and apply our methods to the open question on the complexity of the implication problem of conditional independence.Peer reviewe
Polyteam Semantics
Team semantics is the mathematical framework of modern logics of dependence and independence in which formulae are interpreted by sets of assignments (teams) instead of single assignments as in first-order logic. In order to deepen the fruitful interplay between team semantics and database dependency theory, we define "Polyteam Semantics" in which formulae are evaluated over a family of teams. We begin by defining a novel polyteam variant of dependence atoms and give a finite axiomatisation for the associated implication problem. We also characterise the expressive power of poly-dependence logic by properties of polyteams that are downward closed and definable in existential second-order logic (ESO). The analogous result is shown to hold for poly-independence logic and all ESO-definable properties.Peer reviewe
Parametrised Complexity of Model Checking and Satisfiability in Propositional Dependence Logic
In this paper, we initiate a systematic study of the parametrised complexity
in the field of Dependence Logics which finds its origin in the Dependence
Logic of V\"a\"an\"anen from 2007. We study a propositional variant of this
logic (PDL) and investigate a variety of parametrisations with respect to the
central decision problems. The model checking problem (MC) of PDL is
NP-complete. The subject of this research is to identify a list of
parametrisations (formula-size, treewidth, treedepth, team-size, number of
variables) under which MC becomes fixed-parameter tractable. Furthermore, we
show that the number of disjunctions or the arity of dependence atoms
(dep-arity) as a parameter both yield a paraNP-completeness result. Then, we
consider the satisfiability problem (SAT) showing a different picture: under
team-size, or dep-arity SAT is paraNP-complete whereas under all other
mentioned parameters the problem is in FPT. Finally, we introduce a variant of
the satisfiability problem, asking for teams of a given size, and show for this
problem an almost complete picture.Comment: Update includes refined result
Affect in mathematics education
There are two different uses for the word “affect” in behavioral sciences. Often it is used as an overarching umbrella concept that covers attitudes, beliefs, motivation, emotions, and all other noncognitive aspects of human mind. In this article, however, the word affect is used in a more narrow sense, referring to emotional states and traits. A more technical definition of emotions, states, and traits will follow later.Peer reviewe
Complexity Thresholds in Inclusion Logic
Logics with team semantics provide alternative means for logical
characterization of complexity classes. Both dependence and independence logic
are known to capture non-deterministic polynomial time, and the frontiers of
tractability in these logics are relatively well understood. Inclusion logic is
similar to these team-based logical formalisms with the exception that it
corresponds to deterministic polynomial time in ordered models. In this article
we examine connections between syntactical fragments of inclusion logic and
different complexity classes in terms of two computational problems: maximal
subteam membership and the model checking problem for a fixed inclusion logic
formula. We show that very simple quantifier-free formulae with one or two
inclusion atoms generate instances of these problems that are complete for
(non-deterministic) logarithmic space and polynomial time. Furthermore, we
present a fragment of inclusion logic that captures non-deterministic
logarithmic space in ordered models
- …