Search query: VLSI analogs of neuronal visual processing: a synthesis of form and function

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abstract: This thesis describes the development and testing of a simple visual system fabricated using complementary metal oxide semiconductor (CMOS) very large scale integration (VLSI) technology. This visual system is composed of three subsystems. A silicon retina, fabricated on a single chip, transduces light and performs signal processing in a manner similar to a simple vertebrate retina. A stereocorrespondence chip uses bilateral retinal input to estimate the location of objects in depth. A silicon optic nerve allows communication between chips by a method that preserves the idiom of action potential transmission in the nervous system. Each of these subsystems illuminates various aspects of the relationship between VLSI analogs and their neurobiological counterparts. The overall synthetic visual system demonstrates that analog VLSI can capture a significant portion of the function of neural structures at a systems level, and concomitantly, that incorporating neural architectures leads to new engineering approaches to computation in VLSI. The relationship between neural systems and VLSI is rooted in the shared limitations imposed by computing in similar physical media. The systems discussed in this text support the belief that the physical limitations imposed by the computational medium significantly affect the evolving algorithm. Since circuits are essentially physical structures, I advocate the use of analog VLSI as powerful medium of abstraction, suitable for understanding and expressing the function of real neural systems. The working chip elevates the circuit description to a kind of synthetic formalism. The behaving physical circuit provides a formal test of theories of function that can be expressed in the language of circuits.
author_names: Misha A Mahowald
title: VLSI analogs of neuronal visual processing: a synthesis of form and function
year: 1992

abstract: We have done integration and differentiation with simple, single timeconstant circuits that had ts 1 in the denominator of their transfer functions. These systems gave an exponentially damped response to step or impulse inputs. In Chapter 8, we showed how a second order system can give rise to a sinusoidal response. In this chapter, we will discuss a simple circuit that can generate a sinusoidal response. We call this circuit the second order section; we can use it to generate any response that can be represented by two poles in the complex plane, where the two poles have both real and imaginary parts. With this circuit, we can adjust the positions of the complex conjugate poles anywhere in the plane. The second order circuit is shown in Figure 11.1; it contains two cascaded follower integrator circuits and an extra amplifier. The capacitance C is the same for both stages (C1 C2 C) and the transconductance of the two feed forward amplifiers, A1 and A2, are the same: G1 G2 G (approximately if G is defined as the average of G1 and G2, small differences will have no first order effect on the parameters of the response) We obtain an oscillatory response by adding the feedback amplifier A3. This amplifier has transconductance G3, and its output current is proportional to the difference between V2 and V3, but the sign of the feedback is positive; for small signals, I3 is equal to G3(V2 V3) If we reduce the feedback to zero by shutting off the bias current in A3, each follower integrator circuit will have the transfer function given
author_names: Carver Mead
title: Analog VLSI and neural systems
year: 1989

abstract: From the Publisher: Neuromorphic engineers work to improve the performance of artificial systems through the development of chips and systems that process information collectively using primarily analog circuits. This book presents the central concepts required for the creative and successful design of analog VLSI circuits. The discussion is weighted toward novel circuits that emulate natural signal processing. Unlike most circuits in commercial or industrial applications, these circuits operate mainly in the subthreshold or weak inversion region. Moreover, their functionality is not limited to linear operations, but also encompasses many interesting nonlinear operations similar to those occurring in natural systems. Topics include device physics, linear and nonlinear circuit forms, translinear circuits, photodetectors, floating gate devices, noise analysis, and process technology.
author_names: Shih-Chii Liu

Tobi Delbruck

Jorg Kramer

Giacomo Indiveri

Rodney J Douglas
title: Analog VLSI: Circuits and Principles
year: 2002

abstract: A two dimensional object based analog VLSI model of selective attentional processing has been implemented using a standard 1.2 /spl mu/m CMOS process. This chip extends previous work modeling object based selection and scanning by incorporating the circuity and architectural changes necessary for two dimensional focal plane processing. To balance the need for closely spaced large photodetectors with the space requirements of complex in pixel processing, the chip implements a multiresolution architecture. The system has he ability to group pixels into objects; this grouping is dynamic, driven solely by the segmentation criterion at the input. In the demonstration system, image intensity has been chosen for the input saliency map and the segmentation is based on spatial lowpass filtering followed by an intensity threshold. We present experimental results.
author_names: Charles S Wilson

Tonia G Morris

Stephen P DeWeerth
title: A two dimensional, object based analog VLSI visual attention system
venue: Proceedings 20th Anniversary Conference on Advanced Research in VLSI
year: 1999

abstract: 1. A Neural Processor for Maze Solving. 2 Resistive Fuses: Analog Hardware for Detecting Discontinuities in Early Vision. 3 CMOS Integration of Herault Jutten Cells for Separation of Sources. 4 Circuit Models of Sensory Transduction in the Cochlea. 5 Issues in Analog VLSI and MOS Techniques for Neural Computing. 6 Design and Fabrication of VLSI Components for a General Purpose Analog Neural Computer. 7 A Chip that Focuses an Image on Itself. 8 A Foveated Retina Like Sensor Using CCD Technology. 9 Cooperative Stereo Matching Using Static and Dynamic Image Features. 10 Adaptive Retina.
author_names: Carver Mead

Mohammed Ismail
title: Analog VLSI Implementation of Neural Systems
venue: The Kluwer International Series in Engineering and Computer Science
year: 1989

abstract: An object based analog very large scale integration (VLSI) model of selective attentional processing has been implemented using a standard 2.0 /spl mu/m CMOS process. This chip extends previous work on modeling a saliency map based selection and scanning mechanism to incorporate the ability to group pixels into objects. This grouping, or segmentation, couples the circuitry of the object's pixels to act as a single, larger pixel. The grouping of pixels is dynamic, driven solely by the segmentation criterion at the input. In this demonstration circuit, image intensity has been chosen for the input saliency map and the segmentation is based on spatial low pass filtering followed by an intensity threshold. We present experimental results from a one dimensional implementation of the object based analog VLSI selective attention system.
author_names: Tonia G Morris

Timothy K Horiuchi

Stephen P DeWeerth
title: Object Based Selection Within an Analog VLSI Visual Attention System
year: 1998

abstract: Most models of visual search, whether involving overt eye movements or covert shifts of attention, are based on the concept of a saliency map, that is, an explicit two dimensional map that encodes the saliency or conspicuity of objects in the visual environment. Competition among neurons in this map gives rise to a single winning location that corresponds to the next attended target. Inhibiting this location automatically allows the system to attend to the next most salient location. We describe a detailed computer implementation of such a scheme, focusing on the problem of combining information across modalities, here orientation, intensity and color information, in a purely stimulus driven manner. The model is applied to common psychophysical stimuli as well as to a very demanding visual search task. Its successful performance is used to address the extent to which the primate visual system carries out visual search via one or more such saliency maps and how this can be tested.
author_names: Laurent Itti

Christof Koch
title: A saliency based search mechanism for overt and covert shifts of visual attention
venue: Vision Research
year: 2000

abstract: We describe a modification to our recent model of the action potential which introduces two additional equilibrium points. By using stability analysis we show that one of these equilibrium points is a saddle point from which there are two separatrices which divide the phase plane into two regions. In one region all phase paths approach a limit cycle and in the other all phase paths approach a stable equilibrium point. A consequence of this is that a short depolarizing current pulse will change an initially silent model neuron into one that fires repetitively. Addition of a third equation limits this firing to either an isolated burst or a depolarizing afterpotential. When steady depolarizing current was applied to this model it resulted in periodic bursting. The equations, which were initially developed to explain isolated triggered bursts, therefore provide one of the simplest models of the more general phenomenon of oscillatory burst discharge.
author_names: J L Hindmarsh

Robert M Rose
title: A model of neuronal bursting using three coupled first order differential equations
venue: Proceedings of the Royal Society of London. Series B. Biological Sciences
year: 1984

abstract: Introduction to a Transient World. Fourier Kingdom. Discrete Revolution. Time Meets Frequency. Frames. Wavelet Zoom. Wavelet Bases. Wavelet Packet and Local Cosine Bases. An Approximation Tour. Estimations are Approximations. Transform Coding. Appendix A: Mathematical Complements. Appendix B: Software Toolboxes.
author_names: Stephane Mallat
title: A wavelet tour of signal processing
year: 1998

abstract: After explaining the advantages expected from analog collective computation in solving perceptive tasks, this paper reviews various circuit techniques which are particularly well suited for such an approach. Several examples of working VLSI chips, some of them already used in industrial products, are then briefly presented.
author_names: Eric A Vittoz
title: Analog VLSI for collective computation
venue: 1998 IEEE International Conference on Electronics, Circuits and Systems. Surfing the Waves of Science and Technology (Cat. No.98EX196)
year: 1998