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  • 1
    Digitale Medien
    Digitale Medien
    An overall description of retinotopic mapping in the cat's visual cortex areas 17, 18, and 19 (1985)
    Springer
    Biological cybernetics 52 (1985), S. 45-51 
    Details
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract Mathematical functions are derived which model the retinotopic mapping in the cat's visual cortical areas 17, 18, and 19. All three mappings are simple modifications of a complex power function with an exponent of 0.43. This function is decomposed so as to give an intermediate stage which is common to all three mappings and can be regarded as a model of the lateral geniculate nucleus mapping. The influence of retinotopic mapping on visual receptive fields was studied. The results show that a dependence of the receptive field properties on the position in the visual field is to be expected.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00336934
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  • 2
    Digitale Medien
    Digitale Medien
    A psychophysical and computational analysis of intensity–based stereo (1996)
    Springer
    Biological cybernetics 75 (1996), S. 187-198 
    Details
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract. We describe two psychophysical experiments testing predictions of the square difference mechanism we have previously proposed for intensity–based stereo. Experiment 1 assesses the relative contributions of disparity and contrast to intensity–based stereo by measuring detection thresholds. The product of disparity and contrast at threshold is shown to be constant. In experiment 2, we measure quantitatively the global depth position perceived in stereograms of curved, smoothly shaded surfaces. The results show that disparity averaging over the surface involves a contrast-dependent weighting function. The results from both experiments are consistent with predictions derived from the square difference mechanism. The relation of this mechanism to feature correspondence stereopsis and shape–from–shading is discussed and a general framework for assessing the modularity of stereopsis is presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004220050286
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  • 3
    Digitale Medien
    Digitale Medien
    Is correspondence search in human stereo vision a coarse-to-fine process? (1996)
    Springer
    Biological cybernetics 74 (1996), S. 95-106 
    Details
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract One possible strategy for the solution of the correspondence problem of stereo matching is the coarse-to-fine mechanism: The matching process starts with a lowpassfiltered version of the stereogram where only a few, high-contrast image features can be extracted and the probability of false matches is therefore low. In subsequent stages, information from higher spatial frequencies is used gradually to improve the correspondence data obtained on the coarser scales. Coarse-to-fine strategies predict that information from coarse scale is used to disambiguate matching information on finer scales. We have tested this prediction by means of the wallpaper illusion using periodic intensity-profiles with different matching ambiguities on different spatial scale. Our psychophysical experiments show (i) that unambiguous information at coarse scale is not always used to disambiguate finer scale information, (ii) that unambiguous fine-scale information can be used to disambiguate coarsescale information and (iii) that low spatial frequency is more efficient for disambiguation than higher frequency. We conclude that the human stereo vision system does not always proceed from coarse to fine. As an alternative scheme for scale-space integration, we discuss more symmetric schemes such as maximum likelihood combinations of data from different channels.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00204198
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  • 4
    Digitale Medien
    Digitale Medien
    Inverse perspective mapping simplifies optical flow computation and obstacle detection (1991)
    Springer
    Biological cybernetics 64 (1991), S. 177-185 
    Details
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract We present a scheme for obstacle detection from optical flow which is based on strategies of biological information processing. Optical flow is established by a local “voting” (non-maximum suppression) over the outputs of correlation-type motion detectors similar to those found in the fly visual system. The computational theory of obstacle detection is discussed in terms of space-variances of the motion field. An efficient mechanism for the detection of disturbances in the expected motion field is based on “inverse perspective mapping”, i.e., a coordinate transform or retinotopic mapping applied to the image. It turns out that besides obstacle detection, inverse perspective mapping has additional advantages for regularizing optical flow algorithms. Psychophysical evidence for body-scaled obstacle detection and related neurophysiological results are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00201978
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  • 5
    Digitale Medien
    Digitale Medien
    Human stereovision without localized image features (1995)
    Springer
    Biological cybernetics 72 (1995), S. 279-293 
    Details
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract. Many theories of human stereovision are based on feature matching and the related correspondence problem. In this paper, we present psychophysical experiments indicating that localized image features such as Laplacian zerocrossings, intensity extrema, or centroids are not necessary for binocular depth perception. Smooth one-dimensional intensity profiles were combined into stereograms with mirror-symmetric half-images such that these localized image features were either absent or did not carry stereo information. In a discrimination task, subjects were asked to distinguish between stereograms differing only by an exchange of these half-images (ortho- vs. pseudoscopic stereograms). In a depth ordering task, subjects had to judge which of the two versions appeared in front. Subjects are able to solve both tasks even in the absence of the mentioned image features. The performance is compared to various possible stereo mechanisms. We conclude that localized image features and the correspondences between them are not necessary to perceive stereoscopic depth. One mechanism accounting for our data is correlation or mean square difference.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004220050130
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  • 6
    Digitale Medien
    Digitale Medien
    Editorial: Navigation in biological and artificial systems (2000)
    Springer
    Biological cybernetics 83 (2000), S. 169-170 
    Details
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004220000161
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  • 7
    Digitale Medien
    Digitale Medien
    Population networks: a large-scale framework for modelling cortical neural networks (1996)
    Springer
    Biological cybernetics 75 (1996), S. 441-452 
    Details
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract. Artificial neural networks are usually built on rather few elements such as activation functions, learning rules, and the network topology. When modelling the more complex properties of realistic networks, however, a number of higher-level structural principles become important. In this paper we present a theoretical framework for modelling cortical networks at a high level of abstraction. Based on the notion of a population of neurons, this framework can accommodate the common features of cortical architecture, such as lamination, multiple areas and topographic maps, input segregation, and local variations of the frequency of different cell types (e.g., cytochrome oxidase blobs). The framework is meant primarily for the simulation of activation dynamics; it can also be used to model the neural environment of single cells in a multiscale approach.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004220050309
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  • 8
    Digitale Medien
    Digitale Medien
    Where did I take that snapshot? Scene-based homing by image matching (1998)
    Springer
    Biological cybernetics 79 (1998), S. 191-202 
    Details
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract. In homing tasks, the goal is often not marked by visible objects but must be inferred from the spatial relation to the visual cues in the surrounding scene. The exact computation of the goal direction would require knowledge about the distances to visible landmarks, information, which is not directly available to passive vision systems. However, if prior assumptions about typical distance distributions are used, a snapshot taken at the goal suffices to compute the goal direction from the current view. We show that most existing approaches to scene-based homing implicitly assume an isotropic landmark distribution. As an alternative, we propose a homing scheme that uses parameterized displacement fields. These are obtained from an approximation that incorporates prior knowledge about perspective distortions of the visual environment. A mathematical analysis proves that both approximations do not prevent the schemes from approaching the goal with arbitrary accuracy, but lead to different errors in the computed goal direction. Mobile robot experiments are used to test the theoretical predictions and to demonstrate the practical feasibility of the new approach.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004220050470
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  • 9
    Digitale Medien
    Digitale Medien
    Learning View Graphs for Robot Navigation (1998)
    Springer
    Autonomous robots 5 (1998), S. 111-125 
    Details
    ISSN: 1573-7527
    Schlagwort(e): visual navigation ; topological maps ; environment modeling ; exploration ; cognitive maps ; mobile robots ; omnidirectional sensor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract We present a purely vision-based scheme for learning a topological representation of an open environment. The system represents selected places by local views of the surrounding scene, and finds traversable paths between them. The set of recorded views and their connections are combined into a graph model of the environment. To navigate between views connected in the graph, we employ a homing strategy inspired by findings of insect ethology. In robot experiments, we demonstrate that complex visual exploration and navigation tasks can thus be performed without using metric information.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008821210922
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  • 10
    Digitale Medien
    Digitale Medien
    Human stereovision without localized image features (1995)
    Springer
    Biological cybernetics 72 (1995), S. 279-293 
    Details
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract Many theories of human Stereovision are based on feature matching and the related correspondence problem. In this paper, we present psychophysical experiments indicating that localized image features such as Laplacian zerocrossings, intensity extrema, or centroids are not necessary for binocular depth perception. Smooth one-dimensional intensity profiles were combined into stereograms with mirror-symmetric half-images such that these localized image features were either absent or did not carry stereo information. In a discrimination task, subjects were asked to distinguish between stereograms differing only by an exchange of these half-images (ortho- vs. pseudoscopic stereograms). In a depth ordering task, subjects had to judge which of the two versions appeared in front. Subjects are able to solve both tasks even in the absence of the mentioned image features. The performance is compared to various possible stereo mechanisms. We conclude that localized image features and the correspondences between them are not necessary to perceive stereoscopic depth. One mechanism accounting for our data is correlation or mean square difference.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00202784
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