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Towards the neuronal correlate of visual awareness

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 silicon model of the auditory neural perception of frequency modulated tones

A silicon model of the auditory neural perception of frequen...

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IEEE International Symposium on Circuits and systems (ISCAS)

作者： B.J. Arthur Computation and Neural Systems Program California Institute of Technology Pasadena CA USA

Frequency modulations in acoustic communication signals are thought to encode meaning in many animal species. Recent physiological experiments have elucidated possible neural mechanisms underlying their perception. The system described here attempts to model such mechanisms using subthreshold analog circuitry. It is built with a silicon cochlea and a unidirectional velocity-tuned delay line. Taps from the cochlea couple into the delay line. If the input frequency is modulated in the appropriate direction and right speed, the inputs to the delay line will coincide in time and summate. A similar design was recently used to detect motion in a vision chip.

关键词： Silicon Frequency modulation Delay lines Speech recognition Flexible manufacturing systems Circuits Motion detection Humans Filters Modulation coding

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Analog VLSI circuits for visual motion-based adaptation of post-saccadic drift

Analog VLSI circuits for visual motion-based adaptation of p...

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International Conference on Microelectronics for neural Networks

作者： T.K. Horiuchi C. Koch Computation and Neural Systems Program California Institute of Technology Pasadena CA USA

Using the analog VLSI-based saccadic eye movement system previously developed we investigate the use of biologically realistic error signals to calibrate the system in a manner similar to the primate oculomotor system. In this paper we introduce two new circuit components which are used to perform this task, a resettable-integrator model of the burst generator with a floating-gate structure to provide on-chip storage of analog parameters and a directionally-selective motion detector for detecting post-saccadic drift.

关键词： Very large scale integration Circuits Motion detection Muscles Detectors Eyes Humans Sockets Retina Biology computing

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System implementations of analog VLSI velocity sensors

System implementations of analog VLSI velocity sensors

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International Conference on Microelectronics for neural Networks

作者： G. Indiveri J. Kramer C. Koch Computation and Neural Systems Program California California Institute of Technology Pasadena CA USA

We present three different architectures that make use of analog VLSI velocity sensors for detecting the focus of expansion, time to contact and motion discontinuities respectively. For each of the architectures proposed we describe the functionality of their component modules and their principles of operation. Data measurements obtained from the VLSI chips developed demonstrate their correct performance and their limits of operation.

关键词： Very large scale integration Sensor systems Optical sensors Image motion analysis Sensor arrays Motion detection Focusing Vehicles Computer architecture Image sensors

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Monotonicity hints 96

Monotonicity hints

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Proceedings of the 10th International Conference on neural Information Processing systems

作者： Joseph Sill Yaser S. Abu-Mostafa Computation and Neural Systems program California Institute of Technology EE and CS Deptartments California Institute of Technology

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.

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Stimulating brain but not mind

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Nature 1996年第6598期383卷 301-303页

作者： C. Koch R. B. H. Tootell Computation and Neural Systems Program California Institute of Technology Pasadena USA Massachusetts General Hospital NMR Center Charlestown USA

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Analog VLSI architecture for computing heading direction

Analog VLSI architecture for computing heading direction

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IEEE Symposium on Intelligent Vehicle

作者： G. Indiveri J. Kramer C. Koch Computation and Neural Systems Program Pasadena CA USA

We describe a parallel analog VLSI architecture that integrates optical flow data obtained from arrays of elementary velocity sensors to estimate the direction of heading for pure translational motion sequences. We performed software simulations at different levels of abstraction to evaluate the most important qualitative properties of the optical flow field, determine the best functional operators for the implementation of the architecture and define the numerical values of some of the free parameters present in the hardware implementation. Furthermore we describe the properties of the circuits used in the hardware implementation and the functionality of the elementary motion sensors used to extract the optical flow field. Measurements from the chips developed and software simulation results are provided to show the validity of the followed approach.

关键词： Very large scale integration Computer architecture Analog computers Optical sensors Image motion analysis Sensor arrays Optical arrays Sensor phenomena and characterization Hardware Integrated optics

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TOWARD COLOR IMAGE SEGMENTATION IN ANALOG VLSI - ALGORITHM AND HARDWARE

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INTERNATIONAL JOURNAL OF COMPUTER VISION 1994年第1期12卷 17-42页

作者： PEREZ, F KOCH, C 1. Computation and Neural Systems Program 216-76 California Institute of Technology 91125 Pasadena CA

Standard techniques for segmenting color images are based on finding normalized RGB discontinuities, color histogramming, or clustering techniques in RGB or CIE color spaces. The use of the psychophysical variable hue in HSI space has not been popular due to its numerical instability at low saturations. In this article, we propose the use of a simplified hue description suitable for implementation in analog VLSI. We demonstrate that if the integrated white condition holds, hue is invariant to certain types of highlights, shading, and shadows. This is due to the additive/shift invariance property, a property that other color variables lack. The more restrictive uniformly varying lighting model associated with the multiplicative/scale invariance property shared by both hue and normalized RGB allows invariance to transparencies, and to simple models of shading and shadows. Using binary hue discontinuities in conjunction with first-order type of surface interpolation, we demonstrate these invariant properties and compare them against the performance of RGB, normalized RGB, and CIE color spaces. We argue that working in HSI space offers an effective method for segmenting scenes in the presence of confounding cues due to shading, transparency, highlights, and shadows. Based on this work, we designed and fabricated for the first time an analog CMOS VLSI circuit with on-board phototransistor input that computes normalized color and hue.

关键词： Color image processing

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BAYESIAN MODELING AND CLASSIFICATION OF neural SIGNALS

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neural computation 1994年第5期6卷 1005-1030页

作者： LEWICKI, MS Computation Neural Systems Program California Institute of Technology 216-76 Pasadena CA 91125 USA

Identifying and classifying action potential shapes in extracellular neural waveforms have long been the subject of research, and although several algorithms for this purpose have been successfully applied, their use has been limited by some outstanding problems. The first is how to determine shapes of the action potentials in the waveform and, second, how to decide how many shapes are distinct. A harder problem is that action potentials frequently overlap making difficult both the determination of the shapes and the classification of the spikes. In this report, a solution to each of these problems is obtained by applying Bayesian probability theory. By defining a probabilistic model of the waveform, the probability of both the form and number of spike shapes can be quantified. In addition, this framework is used to obtain an efficient algorithm for the decomposition of arbitrarily complex overlap sequences. This algorithm can extract many times more information than previous methods and facilitates the extracellular investigation of neuronal classes and of interactions within neuronal circuits.

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A model for the neuronal implementation of selective visual attention based on temporal correlation among neurons

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Journal of computational Neuroscience 1994年第1-2期1卷 141-158页

作者： Niebur, Ernst Koch, Christof Computation and Neural Systems Program California Institute of Technology Pasadena 91125 CA United States

We propose a model for the neuronal implementation of selective visual attention based on temporal correlation among groups of neurons. Neurons in primary visual cortex respond to visual stimuli with a Poisson distributed spike train with an appropriate, stimulus-dependent mean firing rate. The spike trains of neurons whose receptive fields do not overlap with the "focus of attention" are distributed according to homogeneous (time-independent) Poisson process with no correlation between action potentials of different neurons. In contrast, spike trains of neurons with receptive fields within the focus of attention are distributed according to non-homogeneous (time-dependent) Poisson processes. Since the short-term average spike rates of all neurons with receptive fields in the focus of attention covary, correlations between these spike trains are introduced which are detected by inhibitory interneurons in V4. These cells, modeled as modified integrate-and-fire neurons, function as coincidence detectors and suppress the response of V4 cells associated with non-attended visual stimuli. The model reproduces quantitatively experimental data obtained in cortical area V4 of monkey by Moran and Desimone (1985). © 1994 Kluwer Academic Publishers.

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