The magnification exponents ¯ occuring in adaptive map formation algorithms like Kohonen's self-organizing feature map deviate for the information theoretically optimal value ¯ = 1 as well as from the values which optimize, e.g., the mean square distortion error (¯ = 1=3 for one-dimensional maps). At the same time, models for categorical perception such as the "perceptual magnet" effect which are based on topographic maps require negative magnification exponents ¯ ! 0. We present an extension of the self-organizing feature map algorithm which utilizes adaptive local learning step sizes to actually control the magnification properties of the map. By change of a single parameter, maps with optimal information transfer, with various minimal reconstruction errors, or with an inverted magnification can be generated. Analytic results on this new algorithm are complemented by numerical simulations. 1. Introduction The representation of information in topographic maps is a common property of...

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The representations of visual hemifields in the extrastriate areas of various species exhibit field discontinuities and islands. We propose that these violations of retinotopy are a developmental consequence of the elongated shape of the respective cortical areas. To substantiate this claim, we investigate a model of activity driven map formation. In agreement with observations, this model yields maps with field discontinuities if the cortical areas exceed a threshold elongation. Moreover, within the same model also island representations in the periphery and of the area centralis can be understood. A multistability of solutions in the model gives a very simple explanation for the observed interindividual variability of maps in cats. The model leads to a prediction for the radial dependence of the areal magnification factor near field discontinuities, which could be accessible for a high precision mapping experiment. Revised Version 14.10.1993 submitted to Biological Cybernetics 1 In...

The primate retina performs nonlinear "image" data reduction while providing a compromise between high resolution where needed, a wide field-of-view, and small output image size. For autonomous robotics, this compromise is useful for developing vision systems with adequate response times. This paper reviews the two classes of models of retino-cortical data reduction used in hardware implementations. The first class reproduces the retina to cortex mapping based on conformal mapping functions. The pixel intensities are averaged in groups called receptive fields (RF's) which are non-overlapping, and the averaging performed is uniform. As is the case in the retina, the size of the RF's increases with distance from the centre of the sensor. Implementations using this class of models are reported to run at video rates (30 frames per second). The second class of models reproduce, in addition to the variable-resolution retino-cortical mapping, the overlap feature of receptive fields of retinal...

this article, we summarize some of the approaches and some of the key results, that have contributed to our current understanding of how early vision works. It is easy to see that this is an extremely large area. The present article cannot be and does not even attempt to be comprehensive on this item. For example,we will commit ourselves almost exclusively on aspects of spatial vision and will not consider many important aspects of temporal coding such as spike and burst synchronization [Eckhorn et al., 1988, Gray et al., 1989, Gray and Singer, 1989, Ritz et al., 1994].

This article presents SERIF, a new model of eye movement control in reading that integrates an established stochastic model of saccade latencies (LATER; R. H. S. Carpenter, 1981) with a fundamental anatomical constraint on reading: the vertically split fovea and the initial projection of information in either visual field to the contralateral hemisphere. The novel features of the model are its simulation of saccade latencies as a race between two stochastic rise-to-threshold LATER units and its probabilistic selection of the target for the next saccade. The model generates simulated eye movement behavior that exhibits important characteristics of actual eye movements made during reading; specifically, simulations produce realistic saccade target distributions and replicate a number of critical reading phenomena, including the effects of word frequency on fixation durations, the inverted optimal viewing position effect, the trade-off between first and second fixation durations of refixated words, and the dependence of parafoveal preview benefit on eccentricity.

this article, we summarize some of the approaches and some of the key results, that have contributed to our current understanding of how early vision works. It is easy to see that this is an extremely large area. The present article cannot be and does not even attempt to be comprehensive on this item. For example, we will commit ourselves almost exclusively to aspects of spatial vision and will not consider many important aspects of temporal coding such as spike and burst synchronization [Eckhorn et al., 1988, Gray et al., 1989, Gray and Singer, 1989, Ritz et al., 1994].

The human visual system does not treat all parts of an image equally: the central segments of an image are processed with a higher resolution than the segments that fall in the visual periphery. These different representations do not usually disrupt our perception of seamless visual space. However, a dramatic temporal/spatial distortion is perceived by observers of the dynamic visual illusion presented in this paper. The illusion accentuates differences between peripheral and central visual processing by juxtaposing global motion information (a descending disk) and local motion information (an internal spin). The temporal/spatial distortion arises when an observer shifts the image of the descending disk from foveal to peripheral vision (or vice versa). We argue that the perceived distortion may influence real-world visual observations, and we present an analysis of the perception of certain pitches in the sport of baseball (the curveball and rising fastball).Visual Illusion Contributes 3 The process of visual perception begins when an image of the external world forms on the retina in the back of the eye (Wandell, 1996). The human visual system does not treat all parts of the image equally; rather, a disproportionate amount of neural processes are dedicated to the central two degrees of the image. At the level of retina, the central region (the fovea) has a higher density of photoreceptors and ganglion cells than does the periphery, and (unlike other mammalian foveae) appears disproportionately populated by midget retinal ganglion cells (Masland, 2001) that have a characteristic morphology unlike other regions of the retina (see Martin & Grünert, 2003). The central overrepresentation compared to the visual

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