: We discuss some of the fundamental issues in the design of highly-parallel, dense, low-power motion sensors in analog VLSI. Since photoreceptor circuits are an integral part of all visual motion sensors, we discuss how the sizing of photosensitive areas can affect the performance of such systems. We review the classic gradient and correlation algorithms and give a survey of analog motion-sensing architectures inspired by them. We calculate how the measurable speed range scales with signal-tonoise ratio for a classic Reichardt sensor with a fixed time constant. We show how this speed range may be improved using a nonlinear filter with an adaptive time constant, constructed out of a diode and a capacitor, and present data from a velocity sensor based on such a filter. Finally, we describe how arrays of such velocity sensors can be employed to compute the heading direction of a moving subject and to estimate the time-to-contact between the sensor and a moving object. Keywords: motion se...

This paper presents a one-dimensional visual sensor, implemented on a single VLSI chip using analog neuromorphic circuits, for selectively detecting and tracking the position of the feature with the highest spatial contrast present in the visual scene. The chip's photoreceptors adapt to stationary backgrounds and can be tuned to respond maximally to specific target velocities. The sensor drastically reduces the amount of data to be transmitted to further processing stages by encoding, in real time, the position of the target in the form of a single continuous-time analog variable. We describe the circuits implementing the sensor and show applications to three examples of tracking tasks: a stand-alone visual tracking system, an active fully analog tracking system, and a mobile platform line-following system.

An object-based analog very large-scale integration (VLSI) model of selective attentional processing has been implemented using a standard 2.0-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.

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. In this paper we present two analog VLSI circuits that implement current mode winner-take-all (WTA) networks with lateral excitation. We describe their principles of operation and compare their performance to previously proposed circuits. The desirable properties of these circuits, namely compactness, low power consumption, collective processing and robustness to noisy inputs make them ideal for system level integration in analog VLSI neuromorphic systems. As application example, we implemented a circuit that employs an adaptive photoreceptor array as the input stage to the WTA network for edge enhancement. Keywords: Analog VLSI, Current mode circuits, WTA networks, Edge detection, Visual attention 1. Introduction The analog VLSI current mode winner-take-all (WTA) circuit, originally presented in [8] is a good example of a very well designed architecture. It is able to process globally all the signals of an input array, it uses a very limited amount of transistors per input node a...

We describe a neuromorphic chip that utilizes transistor heterogeneity, introduced by the fabrication process, to generate orientation maps similar to those imaged in vivo. Our model consists of a recurrent network of excitatory and inhibitory cells in parallel with a push-pull stage. Similar to a previous model the recurrent network displays hotspots of activity that give rise to visual feature maps. Unlike previous work, however, the map for orientation does not depend on the sign of contrast. Instead, signindependent cells driven by both ON and OFF channels anchor the map, while push-pull interactions give rise to sign-preserving cells. These two groups of orientation-selective cells are similar to complex and simple cells observed in V1. 1 Orientation Maps Neurons in visual areas 1 and 2 (V1 and V2) are selectively tuned for a number of

Biological retinas extract spatial and temporal features in an attempt to reduce the complexity of performing visual tasks. We have built and tested a silicon retina which encodes several useful temporal features found in vertebrate retinas. The cells in our silicon retina are selective to direction, highly sensitive to positive contrast changes around an ambient light level, and tuned to a particular velocity. Inhibitory connections in the null direction perform the direction selectivity we desire. This silicon retina is on a 4.6×6.8mm die and consists of a 47×41 array of photoreceptors. 1

We present three di#erent 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 obtainedfrom the VLSI chips developed demonstrate their correct performance and their limits of operation. 1: Introduction Analog velocity sensor circuits have been thoroughly investigated in the past years #19,2,1,7,4,17,5#. Nonetheless, researchers were unable to obtain a device that would simultaneously be compact, robust to background brightness level, insensitivetostimulus contrast and have a wide, unambiguous, range of speed selectivity. Recently novel velocity sensors that are sensitive to low contrast stimuli, independentofcontrast #for intermediate and high contrast values#, selectivetoover 3 orders of magnitude of velocityandover 2 orders of magnitu...

: An analogue-VLSI winner-take-all circuit is enhanced through the addition of hysteretic feedback that emphasizes the spatial locality of competing signals using a resistive network. This circuit has application to tasks in areas such as image processing, in which inputs are not stationary with respect to the circuit array. Introduction Analogue VLSI circuits facilitate the implementation of low-power, real-time visual image processing systems [1]. One task, critical to developing such visual systems that solve real-world problems, is the process of selecting an object and maintaining attention on that selected object [2]. Object selection that produces an output that represents a single stimulus (object) can be accomplished using a winner-take-all circuit. In order to mediate the competition between potential winners, hysteresis can be added to such a winner-takeall circuit through the addition of local feedback to the winning node in the array. The addition of hysteresis enhances ...

Two analog integrated circuits that locate velocity discontinuities in a one-dimensional image are presented. Each circuit combines the image-sensing stage and the motion -processing stage on a single chip. q'he circuits are compax:t arid operate in real time, so that they are suitable for use in mobile systems to perform image segmentation for navigation purposes. Both chips were tested with high-contrast stimuli and showed good performncc.