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  • 1
    Electronic Resource
    Electronic Resource
    Two Methods for Calculating the Responses of Photoreceptors to Moving Objects (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 308-314 
    Details
    ISSN: 1573-9686
    Keywords: Visual acuity ; Motion detection ; Impulse response ; Adapting bump model ; Photoreceptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The responses of photoreceptor cells to moving stimuli are crucial to understanding motion detection in visual systems. However, these responses are not well characterized quantitatively because they result from a combination of spatial optical behavior in the lens systems with temporal behavior in the phototransduction mechanism. While both these processes can now be modeled quite well by relatively simple equations, their combination cannot be easily obtained in a closed form. Here, we present two approaches to this problem, based on well-established models for the lens and photoreceptors systems of the fly compound eye. The first approach leads to a recursive formula for predicting the photoreceptor response to a moving point object. The second method is approximate, but almost equally accurate and more rapid. © 1998 Biomedical Engineering Society. PAC98: 4266Lc, 8722-q, 8710+e
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.58
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  • 2
    Electronic Resource
    Electronic Resource
    Fast-acting compressive and facilitatory nonlinearities in light-adapted fly photoreceptors (1995)
    Springer
    Annals of biomedical engineering 23 (1995), S. 70-77 
    Details
    ISSN: 1573-9686
    Keywords: Phototransduction ; Light adaptation ; Gamma function ; Impulse response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Light-adapted fly photoreceptor cells were stimulated with brief positive and negative contrast flashes (contrast=ΔI/I, I=intensity). Membrane potential responses to a wide range of flash intensities were well-fitted by a static nonlinearity followed by a compartmental model represented by a gamma function. However, the agreement improved if one parameter of the gamma function,n, varied quadratically with input light intensity. Response amplitude and time to peak were estimated from the fitted parameters. Response amplitude varied approximately linearly with contrast but showed nonlinear compression with the largest negative flashes. Reducing the background light level by 3 decades or hyperpolarizing the cell electrically produced stronger nonlinear compression with both contrast polarities. This is probably due to fast voltage-activated K+ channels. Responses to double flashes with varying time separations were well-fitted by summed gamma functions, allowing separation of the individual flash responses. There was no detectable time-dependent interaction between paired positive flashes at all separations. However, the response to two negative flashes was greater than the linear prediction at short separations, and this facilitatory nonlinearity decayed with a time constant of about 1 msec. The facilitation is probably related to resonant behavior in light-adapted photoreceptors and may be due to an IP3-induced intracellular Ca2+ release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368302
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    Paper (German National Licenses)
    Fulltext
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