152 research outputs found
Contextual emergence of intentionality
By means of an intriguing physical example, magnetic surface swimmers, that
can be described in terms of Dennett's intentional stance, I reconstruct a
hierarchy of necessary and sufficient conditions for the applicability of the
intentional strategy. It turns out that the different levels of the intentional
hierarchy are contextually emergent from their respective subjacent levels by
imposing stability constraints upon them. At the lowest level of the hierarchy,
phenomenal physical laws emerge for the coarse-grained description of open,
nonlinear, and dissipative nonequilibrium systems in critical states. One level
higher, dynamic patterns, such as, e.g., magnetic surface swimmers, are
contextually emergent as they are invariant under certain symmetry operations.
Again one level up, these patterns behave apparently rational by selecting
optimal pathways for the dissipation of energy that is delivered by external
gradients. This is in accordance with the restated Second Law of thermodynamics
as a stability criterion. At the highest level, true believers are intentional
systems that are stable under exchanging their observation conditions.Comment: 27 pages; 4 figures (Fig 1. Copyright by American Physical Society);
submitted to Journal of Consciousness Studie
A biophysical observation model for field potentials of networks of leaky integrate-and-fire neurons
We present a biophysical approach for the coupling of neural network activity
as resulting from proper dipole currents of cortical pyramidal neurons to the
electric field in extracellular fluid. Starting from a reduced threecompartment
model of a single pyramidal neuron, we derive an observation model for
dendritic dipole currents in extracellular space and thereby for the dendritic
field potential that contributes to the local field potential of a neural
population. This work aligns and satisfies the widespread dipole assumption
that is motivated by the "open-field" configuration of the dendritic field
potential around cortical pyramidal cells. Our reduced three-compartment scheme
allows to derive networks of leaky integrate-and-fire models, which facilitates
comparison with existing neural network and observation models. In particular,
by means of numerical simulations we compare our approach with an ad hoc model
by Mazzoni et al. [Mazzoni, A., S. Panzeri, N. K. Logothetis, and N. Brunel
(2008). Encoding of naturalistic stimuli by local field potential spectra in
networks of excitatory and inhibitory neurons. PLoS Computational Biology 4
(12), e1000239], and conclude that our biophysically motivated approach yields
substantial improvement.Comment: 31 pages, 4 figure
Recommended from our members
Inverse problems in neural field theory
We study inverse problems in neural field theory, i.e., the construction of synaptic weight kernels yielding a prescribed neural field dynamics. We address the issues of existence, uniqueness, and stability of solutions to the inverse problem for the Amari neural field equation as a special case, and prove that these problems are generally ill-posed. In order to construct solutions to the inverse problem, we first recast the Amari equation into a linear perceptron equation in an infinite-dimensional Banach or Hilbert space. In a second step, we construct sets of biorthogonal function systems allowing the approximation of synaptic weight kernels by a generalized Hebbian learning rule. Numerically, this construction is implemented by the Moore–Penrose pseudoinverse method. We demonstrate the instability of these solutions and use the Tikhonov regularization method for stabilization and to prevent numerical overfitting. We illustrate the stable construction of kernels by means of three instructive examples
Finding needles in haystacks: Symbolic resonance analysis of event-related potentials unveils different processing demands
Previous ERP studies have found an N400–P600 pattern in sentences in which the number of arguments does not match the number of arguments that the verb can take. In the present study, we elaborate on this question by investigating whether the case of the mismatching object argument in German (accusative/direct object versus dative/indirect object) affects processing differently. In general, both types of mismatches elicited a biphasic N400–P600 response in the ERP. However, traditional voltage average analysis was unable to reveal differences between the two mismatching conditions, that is, between a mismatching accusative versus dative. Therefore, we employed a recently developed method on ERP data analysis, the symbolic resonance analysis (SRA), where EEG epochs are symbolically encoded in sequences of three symbols depending on a given parameter, the encoding threshold. We found a larger proportion of threshold crossing events with negative polarity in the N400 time window for a mismatching dative argument compared to a mismatching accusative argument. By contrast, the proportion of threshold crossing events with positive polarity was smaller for dative in the P600 time window. We argue that this difference is due to the phenomenon of “free dative” in German. This result also shows that the SRA provides a useful tool for revealing ERP differences that cannot be discovered using the traditional voltage average analysis
- …