Search PubMed⌕ Search
Home/Archive/PubMed

PubMed · 845514

Processing visual signals with nonlinear spatial filters.

K Wevelsiep
View original source ↗Export metadata ↓

Abstract

The properties of nonlinear spatial filters as a major part of the peripheral nervous system are investigated with respect to processing of two types of signals: a deterministic stepfunction and Graussian noise. The nonlinearity of the nerve cell is treated as a threshold element. It is shown that certain unfavorable characteristics of linear filters do not occur in such nonlinear filters. The basic nonlinear effects of combined space-time-filtering are demonstrated by using bandpass filters. Time-and space-dependent noise is applied to the nonlinear bandpass. The two subsystems formed by linear bandpass section and the threshold are treated separately. Two examples for the application of nonlinear spatial filtering are given.

Explore related subjects

FeedbackForm PerceptionInformation TheoryModels, NeurologicalNerve NetVisual PathwaysVisual PerceptionJournal Article

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

K Wevelsiep. 1977-02-28. Processing visual signals with nonlinear spatial filters.. https://doi.org/10.1007/bf00276354

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed1999

The modularity of biological regulatory networks.

A useful approach to complex regulatory networks consists of modeling their elements and interactions by Boolean equations. In this context, feedback circuits (i.e. circular sequences of interactions) have been shown to play key dynamical roles: whereas positive circuits are able to generate multistationarity, negative circuits may generate oscillatory behavior. In this paper, we principally focus on the case of gene networks. These are represented by fully connected Boolean networks where each element interacts with all elements including itself. Flexibility in network design is introduced by the use of Boolean parameters, one associated with each interaction or group of interactions affecting a given element. Within this formalism, a feedback circuit will generate its typical dynamical behavior (i.e. multistationarity or oscillations) only for appropriate values of some of the logical parameters. Whenever it does, we say that the circuit is 'functional'. More interestingly, this formalism allows the computation of the constraints on the logical parameters to have any feedback circuit functional in a network. Using this methodology, we found that the fraction of the total number of consistent combinations of parameter values that make a circuit functional decreases geometrically with the circuit length. From a biological point of view, this suggests that regulatory networks could be decomposed into small and relatively independent feedback circuits or 'regulatory modules'.

Feedback↗
PubMed1999

The effect of oleic acid on the human ileal brake and its implications for small intestinal transit of tablet formulations.

PURPOSE: A human volunteer study was carried out to investigate whether activation of the ileal brake mechanism affects the transit of tablets through the small intestine. METHODS: Oleic acid, which has previously been shown to activate the brake, was delivered to the small intestine in a modified release capsule at doses of 300 mg, 600 mg and 1200 mg. The effect of the oleic acid was determined by measuring the transit of two sets of radiolabelled tablets by gamma scintigraphy. One set of tablets was dosed with the capsule and the other one hour later. RESULTS: The results show that in the majority of the volunteers small intestinal residence time was greater with the oleic acid than control. The effect was most pronounced in the tablets given concomitantly with the capsule and with the higher doses of oleic acid. CONCLUSIONS: The ileal brake, activated by oleic acid, can slow the transit of tablets through the small intestine.

Feedback↗
PubMed1999

Predictive coding in the visual cortex: a functional interpretation of some extra-classical receptive-field effects.

We describe a model of visual processing in which feedback connections from a higher- to a lower-order visual cortical area carry predictions of lower-level neural activities, whereas the feedforward connections carry the residual errors between the predictions and the actual lower-level activities. When exposed to natural images, a hierarchical network of model neurons implementing such a model developed simple-cell-like receptive fields. A subset of neurons responsible for carrying the residual errors showed endstopping and other extra-classical receptive-field effects. These results suggest that rather than being exclusively feedforward phenomena, nonclassical surround effects in the visual cortex may also result from cortico-cortical feedback as a consequence of the visual system using an efficient hierarchical strategy for encoding natural images.

Feedback↗