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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 70 (1993), S. 1-13 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract We demonstrate that the map of the preferred orientations and the corresponding map of the orientation tuning strengths as measured with optical imaging are not independent, but that band-pass filtering of the preferred orientation map at each location yields a good approximation of the orientation tuning strength. Band-pass filtering is performed by convolving the map of orientation preference with its own autocorrelation function. We suggest an interpretation of the autocorrelation function of the preferred orientations as synaptic coupling function, i.e., synaptic strength as a function of intracortical distance between cortical cells. In developmental models it has been shown previously that a “Mexican hat”-shaped synaptic coupling function (with a shape similar to that of the autocorrelation function) can produce a realistical-looking pattern of preferred orientations. Since optical imaging performs surface averaging, we discuss the possibility that the connection between the two maps is a measurement artifact of optical imaging. Whether this is the case can only be decided by combining electrode penetrations with optical imaging techniques for which we suggest experiments. We present a model for the generation of both maps from a single computational concept. The model is based on inverse Fourier transform of rather simple two-dimensional annulus-shaped spectra which will produce a column structure very similar to real data. Thus, our approach shows that the complex appearance of cortical orientation columns has a rather simple description in the Fourier domain. Our theoretical analysis explains why singularities in the cortex do not have vorticities other than ±1/2, a result which corresponds to recent experimental findings. This study combines the results from several modeling approaches with recently available optical imaging data to construct a model of both aspects (angle and strength) of the cortical orientation column system. This could alter ideas about cortical development if the link between the two maps can be established as a physiological result.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 19 (2004), S. 0 
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In natural vision, the central nervous system actively selects information for detailed processing through mechanisms of visual attention. It is widely held that simple stimulus features such as color, orientation and intensity contribute to the determination of visual salience and thus can act to guide the selection process in a bottom-up fashion. Contrary to this view, Einhäuser, W. & König, P. [(2003) Eur. J. Neurosci., 17, 1089–1097] conclude from their study of human eye movements that luminance contrast does not contribute to the calculation of stimulus salience and that top-down, rather than bottom-up, factors therefore determine attentional allocation in natural scenes. In this article, we dispute their conclusion and argue that the Einhäuser and König study has a number of methodological problems, the most prominent of which is the unintentional introduction of changes in texture contrast. We hypothesize that texture contrast, like luminance contrast, can contribute to the guidance of attention in a bottom-up fashion, and that an appeal to top-down factors is not necessary. To test this hypothesis, we implement a purely bottom-up model of visual selective attention where salience is derived from both luminance and texture contrast. We find that the model can quantitatively account for Einhäuser and König's results and that texture contrast strongly influences attentional guidance in this particular paradigm. The significance of this result for attentional guidance in other paradigms is discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of computational neuroscience 1 (1994), S. 141-158 
    ISSN: 1573-6873
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine , Physics
    Notes: Abstract We propose a model for the neuronal implementation of selective visual attention based on temporal correlation among groups of neurons. Neurons in primary visual cortex respond to visual stimuli with a Poisson distributed spike train with an appropriate, stimulus-dependent mean firing rate. The spike trains of neurons whose receptive fields donot overlap with the “focus of attention” are distributed according to homogeneous (time-independent) Poisson process with no correlation between action potentials of different neurons. In contrast, spike trains of neurons with receptive fields within the focus of attention are distributed according to non-homogeneous (time-dependent) Poisson processes. Since the short-term average spike rates of all neurons with receptive fields in the focus of attention covary, correlations between these spike trains are introduced which are detected by inhibitory interneurons in V4. These cells, modeled as modified integrate-and-fire neurons, function as coincidence detectors and suppress the response of V4 cells associated with non-attended visual stimuli. The model reproduces quantitatively experimental data obtained in cortical area V4 of monkey by Moran and Desimone (1985).
    Type of Medium: Electronic Resource
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