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

作者： Harrison, Reid R. Koch, Christof Computation and Neural Systems Program 139-74 California Institute of Technology Pasadena CA 91125 United States

ISBN: (纸本)0262100762

Flies are capable of rapidly detecting and integrating visual motion information in behaviorly-relevant ways. The first stage of visual motion processing in flies is a retinotopic array of functional units known as elementary motion detectors (EMDs). Several decades ago, Reichardt and colleagues developed a correlation-based model of motion detection that described the behavior of these neural circuits. We have implemented a variant of this model in a 2.0-/im analog CMOS VLSI process. The re-sult is a low-power, continuous-time analog circuit with integrated photoreceptors that responds to motion in real time. The responses of the circuit to drifting sinusoidal gratings qualitatively resemble the temporal frequency response, spatial frequency response, and direction selectivity of motion-sensitive neurons observed in insects. In addition to its possible engineering applications, the circuit could potentially be used as a building block for constructing hardware models of higher-level insect motion integration.

关键词： Frequency response

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A model of early visual processing

A model of early visual processing

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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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Signal detection in noisy weakly-active dendrites 98

Signal detection in noisy weakly-active dendrites

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Proceedings of the 11th International Conference on neural Information Processing systems

作者： Amit Manwani Christof Koch Computation and Neural Systems Program California Institute of Technology Pasadena CA

Here we derive measures quantifying the information loss of a synaptic signal due to the presence of neuronal noise sources, as it electrotonically propagates along a weakly-active dendrite. We model the dendrite as an infinite linear cable, with noise sources distributed along its length. The noise sources we consider are thermal noise, channel noise arising from the stochastic nature of voltage-dependent ionic channels (K+ and Na+) and synaptic noise due to spontaneous background activity. We assess the efficacy of information transfer using a signal detection paradigm where the objective is to detect the presence/absence of a presynaptic spike from the post-synaptic membrane voltage. This allows us to analytically assess the role of each of these noise sources in information transfer. For our choice of parameters, we find that the synaptic noise is the dominant noise source which limits the maximum length over which information be reliably transmitted.

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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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Floating-gate circuits for adaptation of saccadic eye movement accuracy

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ANALOG INTEGRATED CIRCUITS AND SIGNAL PROCESSING 1997年第1-2期13卷 69-78页

作者： Horiuchi, TK Koch, C Computation and Neural Systems Program California Institute of Technology Pasadena

In this paper we describe an analog VLSI circuit, fabricated using a standard 2 mu m, n-well, BiCMOS process, which utilizes floating-gate structures for non-volatile, on-chip, analog parameter storage. This circuit is designed to operate in the context of a hardware model of the primate oculomotor system and performs visually-guided, saccadic adaptation. The chip contains a one-dimensional array of photoreceptors and floating-gate circuits which are used to map retinal positions to motor output commands. The system's functionality is demonstrated by training the chip with several different mapping functions using a supervised-learning technique.

关键词： neuromorphic analog VLSI saccadic eye movements learning floating-gate short-term adaptation

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Shunting inhibition does not have a divisive effect on firing rates

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neural computation 1997年第5期9卷 1001-1013页

作者： Holt, GR Koch, C Computation and Neural Systems Program California Institute of Technology Pasadena CA 91125 U.S.A.

Shunting inhibition, a conductance increase with a reversal potential close to the resting potential of the cell, has been shown to have a divisive effect on subthreshold excitatory postsynaptic potential amplitudes. It has therefore been assumed to have the same divisive effect on firing rates. We show that shunting inhibition actually has a subtractive effect on the firing rate in most circumstances. Averaged over several interspike intervals, the spiking mechanism effectively clamps the somatic membrane potential to a value significantly above the resting potential, so that the current through the shunting conductance is approximately independent of the firing rate. This leads to a subtractive rather than a divisive effect. In addition, at distal synapses, shunting inhibition will also have an approximately subtractive effect if the excitatory conductance is not small compared to the inhibitory conductance. Therefore regulating a cell's passive membrane conductance-for instance, via massive feedback-is not an adequate mechanism for normalizing or scaling its output.

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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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Monotonicity hints

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10th Annual Conference on neural Information Processing systems, NIPS 1996

作者： Sill, Joseph Abu-Mostafa, Yaser S. Computation and Neural Systems Program California Institute of Technology United States EE Department California Institute of Technology United States

ISBN: (纸本)0262100657

A hint is any piece of side information about the target function to be learned. We consider the monotonicity hint, which states that the function to be learned is monotonic in some or all of the input variables. The application of monotonicity hints is demonstrated on two real-world problems- a credit card application task, and a problem in medical diagnosis. A measure of the monotonicity error of a candidate function is defined and an objective function for the enforcement of monotonicity is derived from Bayesian principles. We report experimental results which show that using monotonicity hints leads to a statistically significant improvement in performance on both problems.

关键词： Diagnosis

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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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