67,284 research outputs found
fMRI Evidence for Modality-Specific Processing of Conceptual Knowledge on Six Modalities
Traditional theories assume that amodal representations, such as feature lists and semantic
networks, represent conceptual knowledge about the world. According to this view, the
sensory, motor, and introspective states that arise during perception and action are irrelevant
to representing knowledge. Instead the conceptual system lies outside modality-specific
systems and operates according to different principles. Increasingly, however, researchers
report that modality-specific systems become active during purely conceptual tasks,
suggesting that these systems play central roles in representing knowledge (for a review, see
Martin, 2001, Handbook of Functional Neuroimaging of Cognition). In particular,
researchers report that the visual system becomes active while processing visual properties,
and that the motor system becomes active while processing action properties. The present
study corroborates and extends these findings. During fMRI, subjects verified whether or not
properties could potentially be true of concepts (e.g., BLENDER-loud). Subjects received
only linguistic stimuli, and nothing was said about using imagery. Highly related false
properties were used on false trials to block word association strategies (e.g., BUFFALOwinged).
To assess the full extent of the modality-specific hypothesis, properties were
verified on each of six modalities. Examples include GEMSTONE-glittering (vision),
BLENDER-loud (audition), FAUCET-turned (motor), MARBLE-cool (touch),
CUCUMBER-bland (taste), and SOAP-perfumed (smell). Neural activity during property
verification was compared to a lexical decision baseline. For all six sets of the modalityspecific
properties, significant activation was observed in the respective neural system.
Finding modality-specific processing across six modalities contributes to the growing
conclusion that knowledge is grounded in modality-specific systems of the brain
A contrasting look at self-organization in the Internet and next-generation communication networks
This article examines contrasting notions of self-organization in the Internet and next-generation communication networks, by reviewing in some detail recent evidence regarding several of the more popular attempts to explain prominent features of Internet structure and behavior as "emergent phenomena." In these examples, what might appear to the nonexpert as "emergent self-organization" in the Internet actually results from well conceived (albeit perhaps ad hoc) design, with explanations that are mathematically rigorous, in agreement with engineering reality, and fully consistent with network measurements. These examples serve as concrete starting points from which networking researchers can assess whether or not explanations involving self-organization are relevant or appropriate in the context of next-generation communication networks, while also highlighting the main differences between approaches to self-organization that are rooted in engineering design vs. those inspired by statistical physics
Empirical Analysis of the Necessary and Sufficient Conditions of the Echo State Property
The Echo State Network (ESN) is a specific recurrent network, which has
gained popularity during the last years. The model has a recurrent network
named reservoir, that is fixed during the learning process. The reservoir is
used for transforming the input space in a larger space. A fundamental property
that provokes an impact on the model accuracy is the Echo State Property (ESP).
There are two main theoretical results related to the ESP. First, a sufficient
condition for the ESP existence that involves the singular values of the
reservoir matrix. Second, a necessary condition for the ESP. The ESP can be
violated according to the spectral radius value of the reservoir matrix. There
is a theoretical gap between these necessary and sufficient conditions. This
article presents an empirical analysis of the accuracy and the projections of
reservoirs that satisfy this theoretical gap. It gives some insights about the
generation of the reservoir matrix. From previous works, it is already known
that the optimal accuracy is obtained near to the border of stability control
of the dynamics. Then, according to our empirical results, we can see that this
border seems to be closer to the sufficient conditions than to the necessary
conditions of the ESP.Comment: 23 pages, 14 figures, accepted paper for the IEEE IJCNN, 201
Integration of continuous-time dynamics in a spiking neural network simulator
Contemporary modeling approaches to the dynamics of neural networks consider
two main classes of models: biologically grounded spiking neurons and
functionally inspired rate-based units. The unified simulation framework
presented here supports the combination of the two for multi-scale modeling
approaches, the quantitative validation of mean-field approaches by spiking
network simulations, and an increase in reliability by usage of the same
simulation code and the same network model specifications for both model
classes. While most efficient spiking simulations rely on the communication of
discrete events, rate models require time-continuous interactions between
neurons. Exploiting the conceptual similarity to the inclusion of gap junctions
in spiking network simulations, we arrive at a reference implementation of
instantaneous and delayed interactions between rate-based models in a spiking
network simulator. The separation of rate dynamics from the general connection
and communication infrastructure ensures flexibility of the framework. We
further demonstrate the broad applicability of the framework by considering
various examples from the literature ranging from random networks to neural
field models. The study provides the prerequisite for interactions between
rate-based and spiking models in a joint simulation
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Evolutionary optimization within an intelligent hybrid system for design integration
An intelligent hybrid approach has been developed to integrate various stages in total design, including formulation of product design specifications, conceptual design, detail design, and manufacture. The integration is achieved by blending multiple artificial intelligence (AI) techniques and CAD/CAE/CAM into a single environment. It has been applied into power transmission system design. In addition to knowledge-based systems and artificial neural networks, another AI technique, genetic algorithms (GAs), are involved in the approach. The GA is used to conduct optimization tasks: (1) searching the best combination of design parameters to obtain optimum design of gears, and (2) optimization of the architecture of the artificial neural networks used in the hybrid system. In this paper, after a brief overview of the intelligent hybrid system, the GA applications are described in detail
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