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At least 55 records · Page 3Linked to original sources
PubMed2006

Dynamics and topographic organization of recursive self-organizing maps.

Recently there has been an outburst of interest in extending topographic maps of vectorial data to more general data structures, such as sequences or trees. However, there is no general consensus as to how best to process sequences using topographic maps, and this topic remains an active focus of neurocomputational research. The representational capabilities and internal representations of the models are not well understood. Here, we rigorously analyze a generalization of the self-organizing map (SOM) for processing sequential data, recursive SOM(RecSOM) (Voegtlin, 2002), as a nonautonomous dynamical system consisting of a set of fixed input maps. We argue that contractive fixed-input maps are likely to produce Markovian organizations of receptive fields on the RecSOM map. We derive bounds on parameter beta (weighting the importance of importing past information when processing sequences) under which contractiveness of the fixed-input maps is guaranteed. Some generalizations of SOM contain a dynamic module responsible for processing temporal contexts as an integral part of the model. We show that Markovian topographic maps of sequential data can be produced using a simple fixed (nonadaptable) dynamic module externally feeding a standard topographic model designed to process static vectorial data of fixed dimensionality (e.g., SOM). However, by allowing trainable feedback connections, one can obtain Markovian maps with superior memory depth and topography preservation. We elaborate on the importance of non-Markovian organizations in topographic maps of sequential data.

Algorithms↗
PubMedDate not supplied

New approaches in brain morphometry.

The complexity and variability of the human brain across subjects is so great that reliance on maps and atlases is essential to effectively manipulate, analyze, and interpret brain data. Central to these tasks is the construction of averages, templates, and models to describe how the brain and its component parts are organized. Design of appropriate reference systems for human brain data presents considerable challenges because these systems must capture how brain structure and function vary in large populations, across age and gender, in different disease states, across imaging modalities, and even across species. The authors introduce the topic of brain maps as applied to a variety of questions and problems in health and disease and include a brief survey of the types of maps relevant to mental disorders, including maps that capture dynamic patterns of brain change in dementia.

Brain↗
PubMed1989

Mapping population data from zone centroid locations.

The author describes the difficulties associated with the use of maps to represent census data. "A review of the problems associated with population mapping is followed by a discussion of [an alternative method known as] a raster method for handling census data, based on population-weighted centroids, and its implications for GIS "[geographic information systems]." The geographical scope is worldwide, with an example provided using data for Wales.

Developed Countries↗
PubMed2005

CiteSpace II: visualization and knowledge discovery in bibliographic databases.

This article presents a description and case study of CiteSpace II, a Java application which supports visual exploration with knowledge discovery in bibliographic databases. Highly cited and pivotal documents, areas of specialization within a knowledge domain, and emergence of research topics are visually mapped through a progressive knowledge domain visualization approach to detecting and visualizing trends and patterns in scientific literature. The test case in this study is progressive knowledge domain visualization of the field of medical informatics. Datasets based on publications from twelve journals in the medical informatics field covering the time period from 1964-2004 were extracted from PubMed and Web of Science (WOS) and developed as testbeds for evaluation of the CiteSpace system. Two resulting document-term co-citation and MeSH term co-occurrence visualizations are qualitatively evaluated for identification of pivotal documents, areas of specialization, and research trends. Practical applications in bio-medical research settings are discussed.

Algorithms↗
PubMed2005

Evaluation of two dependency parsers on biomedical corpus targeted at protein-protein interactions.

We present an evaluation of Link Grammar and Connexor Machinese Syntax, two major broad-coverage dependency parsers, on a custom hand-annotated corpus consisting of sentences regarding protein-protein interactions. In the evaluation, we apply the notion of an interaction subgraph, which is the subgraph of a dependency graph expressing a protein-protein interaction. We measure the performance of the parsers for recovery of individual dependencies, fully correct parses, and interaction subgraphs. For Link Grammar, an open system that can be inspected in detail, we further perform a comprehensive failure analysis, report specific causes of error, and suggest potential modifications to the grammar. We find that both parsers perform worse on biomedical English than previously reported on general English. While Connexor Machinese Syntax significantly outperforms Link Grammar, the failure analysis suggests specific ways in which the latter could be modified for better performance in the domain.

Abstracting and Indexing↗
PubMedDate not supplied

Face identification using one spike per neuron: resistance to image degradations.

The short response latencies of face selective neurons in the inferotemporal cortex impose major constraints on models of visual processing. It appears that visual information must essentially propagate in a feed-forward fashion with most neurons only having time to fire one spike. We hypothesize that flashed stimuli can be encoded by the order of firing of ganglion cells in the retina and propose a neuronal mechanism, that could be related to fast shunting inhibition, to decode such information. Based on these assumptions, we built a three-layered neural network of retino-topically organized neuronal maps. We showed, by using a learning rule involving spike timing dependant plasticity, that neuronal maps in the output layer can be trained to recognize natural photographs of faces. Not only was the model able to generalize to novel views of the same faces, it was also remarkably resistant to image noise and reductions in contrast.

Action Potentials↗
PubMedDate not supplied

Some benchmark searches for testing search capabilities and medical coverage of internet discovery tools.

The past few years have seen a proliferation of search engines for the World Wide Web (WWW), as well as a growing number of specialized subject directories geared to the needs of health care professionals. Yet documentation on scope, coverage, and search features is often uneven at best; and even documented search features may not perform as advertised. This paper will present a group of sample searches to assist users in gauging database size, determining default search operators, and testing for the presence of advanced search features such as case sensitivity, stemming, and concept mapping for medical topics on English-language web sites.

Databases, Factual↗
PubMed2005

Visual exploration of landmarks and trends in the medical informatics literature.

This study presents preliminary results from a visual study of a new dataset of forty years of citation data from publications of twelve journals in the medical informatics field covering the time period from 1964-2004. Highly cited and pivotal documents, areas of specialization within medical informatics, and emergence of research topics are visually mapped through a progressive knowledge domain visualization approach to detecting and visualizing trends and patterns in scientific literature.

Bibliometrics↗
PubMed1998

Rapid termination of intraoperative stimulation-evoked seizures with application of cold Ringer's lactate to the cortex. Technical note.

One major risk of intraoperative stimulation mapping is the production of stimulation-evoked seizures. Cold Ringer's lactate solution was applied directly to the irritated cortex in 22 patients with stimulation-induced seizures that occurred during intraoperative brain mapping procedures. The irrigation rapidly and reliably terminated these simple partial seizures and eliminated the need for intravenously administered short-acting barbiturates with antiepileptic properties. The authors describe a practical and simple method for controlling stimulation-induced seizure activity during brain mapping procedures.

Administration, Topical↗