Basic Difference Between Brain and Computer: Integration of Asynchronous Processes Implemented as Hardware Model of the Retina

There exists a common view that the brain acts like a Turing machine: The machine reads information from an infinite tape (sensory data) and, on the basis of the machine's state and information from the tape, an action (decision) is made. The main problem with this model lies in how to synchronize a large number of tapes in an adaptive way so that the machine is able to accomplish tasks such as object classification. We propose that such mechanisms exist already in the eye. A popular view is that the retina, typically associated with high gain and adaptation for light processing, is actually performing local preprocessing by means of its center-surround receptive field. We would like to show another property of the retina: The ability to integrate many independent processes. We believe that this integration is implemented by synchronization of neuronal oscillations. In this paper, we present a model of the retina consisting of a series of coupled oscillators which can synchronize on several scales. Synchronization is an analog process which is converted into a digital spike train in the output of the retina. We have developed a hardware implementation of this model, which enables us to carry out rapid simulation of multineuron oscillatory dynamics. We show that the properties of the spike trains in our model are similar to those found in vivo in the cat retina     

Activity of common marmosets (Callithrix jacchus) in limited spaces: Hand movement characteristics.

The increasing popularity of marmoset monkeys (Callithrix jacchus) in anatomical, behavioral, and electrophysiological studies has called for a detailed analysis of their natural behavior within limited spaces. In the present study, the authors analyzed hand movements during horizontal and vertical progressions in a cylinder. The trajectory of each hand covered the entire cylinder floor during horizontal progressions and the entire cylinder wall during vertical progressions. Different marmosets have different patterns of hand movement. The average maximum angle of hand movements for all marmosets during horizontal and vertical progressions oscillates, although the average over time is constant and similar for both hands, whereas head movements during horizontal progressions become smaller with successive progressions. Another observed difference between rats and monkeys was in the size of head and hand movements at the beginning of each experimental session. During the 1st horizontal progression, all marmosets moved their heads to a greater extent than their hands. This sequential head and hand movement is referred as bistable behavior. The bistable pattern of motor behavior, which was also observed in successive progressions, may be derived from an inherent fear of predators or exploratory interest of a novel environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Vision: does top-down processing help us to see?

Anatomical studies of the visual cortex have identified massive back-projecting pathways. Theoretical studies suggest how such pathways may play important roles in vision by mediating 'top-down' processing, in which information from a relatively high level is fed back to early visual stages.     

A new class of eigenfunction expansion methods for fastfrequency-domain analysis of waveguides

This paper presents a new class of algorithms for a fast calculation of dispersion characteristics in inhomogeneously loaded strictly bidirectional waveguides. The algorithms use the method of moments to convert the wave equation to a matrix eigenvalue problem using, as a basis, a set of known solutions determined for a few selected points from the ω-β diagram. Depending on the choice of points for the basis and the testing functions, several algorithms are derived, each leading to extremely simple expressions for the calculation of the matrix elements