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11th Annual Conference on neural Information Processing systems, NIPS 1997

作者： Itti, Laurent Braun, Jocheri Lee, Dale K. Koch, Christof Computation and Neural Systems California Institute of Technology MSG 139-74 Pasadena CA 91125 United States

ISBN: (纸本)0262100762

We propose a model for early visual processing in primates. The model consists of a population of linear spatial filters which interact through non-linear excitatory and inhibitory pooling. Statistical estimation theory is then used to derive human psychophysical thresholds from the responses of the entire population of units. The model is able to reproduce human thresholds for contrast and ori-entation discrimination tasks, and to predict contrast thresholds in the presence of masks of varying orientation and spatial frequency.

关键词： Mammals

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Solvable model for spatiotemporal chaos

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Physical Review E 1998年第1期57卷 388-388页

作者： R. O. Grigoriev H. G. Schuster []Condensed Matter Physics 114-36 and Neural Systems Program 139-74 California Institute of Technology Pasadena California 91125

We show that the dynamical behavior of a coupled map lattice where the individual maps are Bernoulli shift maps can be solved analytically for integer couplings. We calculate the invariant density of the system and show that it displays a nontrivial spatial behavior. We also introduce and calculate a generalized spatiotemporal correlation function.

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Floating-gate CMOS analog memory cell array

Floating-gate CMOS analog memory cell array

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IEEE International Symposium on Circuits and systems (ISCAS)

作者： R.R. Harrison P. Hasler B.A. Minch Computation and Neural Systems Program 139-74 California Institute of Technology NASA Pasadena CA USA Department of Electrical and Computer Engineering Georgia Institute of Technology Atlanta GA USA School of Electrical Engineering Cornell University Ithaca NY USA

The complexity of analog VLSI systems is often limited by the number of pins on a chip rather than by the die area. Currently, many analog parameters and biases are stored off chip. Moving parameter storage on chip could save pins and allow us to create complex programmable analog systems. In this paper, we present a design for an on-chip non-volatile analog memory cell that can be configured in addressable arrays and programmed easily. We use floating-gate MOS transistors to store charge, and we use the processes of tunneling and hot-electron injection to program values. We achieve greater than 13-bit precision with no crosstalk between memory cells.

关键词： Nonvolatile memory Analog memory Pins Voltage Potentiometers Tunneling Very large scale integration Secondary generated hot electron injection Analog computers CMOS technology

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Control of chaos by oscillating feedback

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Physical Review E 1997年第6期56卷 6410-6410页

作者： H. G. Schuster M. B. Stemmler Computation and Neural Systems Program California Institute of Technology 139-74 Pasadena California 91125

Parametric feedback control of chaos relies on detailed knowledge of the locations of unstable periodic orbits. We show that unstable periodic orbits of dynamical systems with unknown locations but known periodicity τ can be stabilized by an oscillating feedback term proportional to ɛt (x→t−x→t−τ), where x→t is the location of the trajectory at time t and ɛt is periodic in time. Periodic feedback overcomes the limitations of Giona’s theorem [Nonlinearity 4, 911 (1991)], which states that constant feedback (i.e., a time-independent ɛ) can stabilize an unstable periodic orbit only if the stability matrix has no positive eigenvalues greater than unity. As an application of oscillating feedback, we use it to stabilize the memory patterns in an associative memory (Hopfield [Proc. Natl. Acad. Sci. USA 79, 2554 (1982); 81, 3088 (1984)]) network, thereby enhancing the total capacity of the memory device. We extend our method to high-dimensional systems described by differential equations; in this framework, it is possible to stabilize the spatiotemporal chaos generated by the Kuramoto-Sivashinsky equation [G. J. Sivashinsky and D. M. Michelson, Prog. Theor. Phys. 63, 2122 (1980)].

关键词： Dynamics

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Pinning Control of Spatiotemporal Chaos

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Physical Review Letters 1997年第15期79卷 2795-2795页

作者： R. O. Grigoriev M. C. Cross H. G. Schuster Condensed Matter Physics 114-36 and Neural Systems Program 139-74 California Institute of Technology Pasadena California 91125

Linear control theory is used to develop an improved localized control scheme for spatially extended chaotic systems, which is applied to a coupled map lattice as an example. The optimal arrangement of the control sites is shown to depend on the symmetry properties of the system, while their minimal density depends on the strength of noise in the system. The method is shown to work in any region of parameter space and requires a significantly smaller number of controllers compared to the method proposed earlier by Hu and Qu [Phys. Rev. Lett. 72, 68 (1994)]. A nonlinear generalization of the method for a 1D lattice is also presented.

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TOWARDS ARTICULATORY SPEECH RECOGNITION: LEARNING SMOOTH MAPS TO RECOVER ARTICULATOR INFORMATION 5

TOWARDS ARTICULATORY SPEECH RECOGNITION: LEARNING SMOOTH MAP...

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5th European Conference on Speech Communication and Technology, EUROSPEECH 1997

作者： Roweis, Sam Alwan, Abeer Computation and Neural Systems California Institute of Technology United States Department of Electrical Engineering University of California Los Angeles United States California Institute of Technology Mail Code 139-74 PasadenaCA91125 United States

We present a novel method for recovering articulator movements from speech acoustics based on a constrained form [9] of a hidden Markov model. The model attempts to explain sequences of high dimensional data using smooth and slow trajectories in a latent variable space. The key insight is that this continuity constraint when applied to speech helps to solve the "ill-posed" problem of acoustic to articulatory mapping. By working with sequences of spectra rather than looking only at individual spectra, it is possible to choose between competing articulatory configurations for any given spectrum by selecting the configuration "closest" to those at nearby times. We present results of applying this algorithm to recover articulator movements from acoustics using data from the Wisconsin X-ray microbeam project [3]. We find that the recovered traces are highly correlated with the measured articulator movements under a single linear transform. Such recovered traces have the potential to be used for speech recognition, an application we are currently investigating. © 1997 5th European Conference on Speech Communication and Technology, EUROSPEECH 1997. All rights reserved.

关键词： Hidden Markov models

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Towards the neuronal correlate of visual awareness

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CURRENT OPINION IN NEUROBIOLOGY 1996年第2期6卷 158-164页

作者： Koch, C Braun, J Computation and Neural Systems Program 139-74 California Institute of Technology Pasadena California 91125 USA

Several encouraging developments towards identifying the neuronal correlate of visual awareness have emerged recently. Increasingly sophisticated behavioral paradigms permit the study of visual awareness in humans as well as in non-human primates. In patients with anatomically restricted lesions in striate and extrastriate cortex, highly informative deficits of visual awareness are observed. Similar deficits can be obtained in normal observers with a novel class of psychophysical displays. Taken together, these results suggest that the contents of visual awareness reflect neuronal activity in certain extrastriate, but not in striate, visual cortical areas.

关键词： Animals Awareness Brain Diseases Humans Neurons Reference Values Research Support U.S. Gov't Non-P.H.S. Visual Cortex Visual Perception

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A single spike suffices: The simplest form of stochastic resonance in model neurons

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NETWORK-computation IN neural systems 1996年第4期7卷 687-716页

作者： Stemmler, M Computation and Neural Systems California Institute of Technology 139-74 Pasadena CA 91125 USA

Input noise, defined as the root mean square of the fluctuations in the input, typically limits the performance of any system in engineering or biology. We show that three different performance measures scale identically as a function of the noise in a simple model of neuronal spiking that has both a voltage and current threshold. These performance measures are: the probability of correctly detecting a constant input in a limited time, the signal-to-noise ratio in response to sinusoidal input, and the mutual information between an arbitrarily varying input and the output spike train of the model neuron. Of these, detecting a constant signal is the simplest and most fundamental quantity. For subthreshold signals, the model exhibits stochastic resonance, a non-zero noise amplitude that optimally enhances signal detection. in this case, noise paradoxically does not limit but instead improves performance. This resonance arises through the conjunction of two competing mechanisms: the noise-induced linearization ('dithering') of the model's firing rate and the increase in the variability of the number of spikes in the output. Even though the noise amplitude dwarfs the signal, detection of a weak constant signal using stochastic resonance is still possible when the signal elicits on average only one additional spike. Stochastic resonance could thus play a role in neurobiological sensory systems, where speed is of the utmost importance and averaging over many individual spikes is not possible.

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Control of Selective Visual Attention: Modeling the "Where" Pathway 8

Control of Selective Visual Attention: Modeling the "Where" ...

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8th International Conference on neural Information Processing systems, NIPS 1995

作者： Niebur, Ernst Koch, Christof Computation and Neural Systems 139-74 California Institute of Technology United States

Intermediate and higher vision processes require selection of a subset of the available sensory information before further processing. Usually, this selection is implemented in the form of a spatially circumscribed region of the visual field, the so-called "focus of attention" which scans the visual scene dependent on the input and on the attentional state of the subject. We here present a model for the control of the focus of attention in primates, based on a saliency map. This mechanism is not only expected to model the functionality of biological vision but also to be essential for the understanding of complex scenes in machine vision. © NIPS 1995: Proceedings of the 8th International Conference on neural Information Processing systems. All rights reserved.

关键词： Mammals

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Adaptive Retina with Center-Surround Receptive Field 8

Adaptive Retina with Center-Surround Receptive Field

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8th International Conference on neural Information Processing systems, NIPS 1995

作者： Liu, Shih-Chii Boahen, Kwabena Computation and Neural Systems 139-74 California Institute of Technology PasadenaCA91125 United States

Both vertebrate and invertebrate retinas are highly efficient in extracting contrast independent of the background intensity over five or more decades. This efficiency has been rendered possible by the adaptation of the DC operating point to the background intensity while maintaining high gain transient responses. The centersurround properties of the retina allows the system to extract information at the edges in the image. This silicon retina models the adaptation properties of the receptors and the antagonistic centersurround properties of the laminar cells of the invertebrate retina and the outer-plexiform layer of the vertebrate retina. We also illustrate the spatio-temporal responses of the silicon retina on moving bars. The chip has 59x64 pixels on a 6.9x6.8mm'2 die and it is fabricated in 2 μm n-well technology. © NIPS 1995: Proceedings of the 8th International Conference on neural Information Processing systems. All rights reserved.

关键词： Transient analysis

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