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  • 1
    Electronic Resource
    Electronic Resource
    Butterfly optics exceed the theoretical limits of conventional apposition eyes (1987)
    Springer
    Biological cybernetics 57 (1987), S. 159-168 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Optical experiments on butterfly compound eyes show that they have angular sensitivities narrower than expected from conventional apposition eyes. This superior performance is explained by a theoretical model where the cone stalk is considered as a modecoupling device. In this model the Airy diffraction pattern of the corneal facet excites a combination of the two waveguide modes LP01 and LP02. When the two modes propagate through the cone stalk the power of LP02 is transferred to LP01 alone which is supported by the rhabdom. This mechanism produces a higher on-axis sensitivity and a narrower angular sensitivity than conventional apposition optics. Several predictions of the model were confirmed experimentally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00364148
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  • 2
    Electronic Resource
    Electronic Resource
    A theory of maximizing sensory information (1992)
    Springer
    Biological cybernetics 68 (1992), S. 23-29 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract A theory is developed on the assumption that early sensory processing aims at maximizing the information rate in the channels connecting the sensory system to more central parts of the brain, where it is assumed that these channels are noisy and have a limited dynamic range. Given a stimulus power spectrum, the theory enables the computation of filters accomplishing this maximizing of information. Resulting filters are band-pass or high-pass at high signal-to-noise ratios, and low-pass at low signal-to-noise ratios. In spatial vision this corresponds to lateral inhibition and pooling, respectively. The filters comply with Weber's law over a considerable range of signal-to-noise ratios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203134
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  • 3
    Electronic Resource
    Electronic Resource
    An efficient algorithm for cable theory, applied to blowfly photoreceptor cells and LMC's (1986)
    Springer
    Biological cybernetics 54 (1986), S. 301-311 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract A both simple and efficient algorithm is presented that yields the voltages and currents in an arbitrary cable structure. The algorithm consists of the following steps: 1. The cable structure is divided into homogeneous cable segments; 2. Each cable segment is considered as a two-port, and replaced by an equivalent circuit consisting of discrete elements; 3. The resulting equivalent scheme of the whole cable structure is solved with an algorithm for ladder networks (or, if the structure is not tree-like, with a network analysis program), which yields the input and output voltages and currents of each cable segment; and if required 4. The voltage and current distribution in each segment is determined from the input and output voltages and currents. The algorithm is applied to blowfly photoreceptor cells that are electrically coupled, and to blowfly Large Monopolar Cells. For LMC's it is shown that the loads at the input and output sides of the axon determine whether unidirectional or bidirectional signal transmission occurs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318426
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  • 4
    Electronic Resource
    Electronic Resource
    Waveguide theory applied to optically measured angular sensitivities of fly photoreceptors (1984)
    Springer
    Journal of comparative physiology 154 (1984), S. 761-771 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Farfield radiation patterns of single ommatidia of the fly,Calliphora erythrocephala, have been photographed. Clear radiation patterns of the first and the second waveguide mode have been observed. 2. According to theory, the shape of the (optical) angular sensitivity of a photoreceptor equals the shape of its farfield radiation pattern, at least for a monomode fiber. 3. The farfield radiation patterns of single photoreceptors have been evaluated quantitatively by means of microdensitometry and have been compared with theoretical calculations according to a lens-waveguide model. Theory and experiment are in good accordance for different wavelengths, different lens apertures, and different photoreceptor diameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00610676
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  • 5
    Electronic Resource
    Electronic Resource
    On spiking units in the first optic chiasm of the blowfly (1993)
    Springer
    Journal of comparative physiology 173 (1993), S. 187-192 
    Details
    ISSN: 1432-1351
    Keywords: Blowfly ; Sustaining unit ; Lamina ; Spatio ; temporal processing ; On-off unit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We recorded from the spiking sustaining unit in the optic chiasm between lamina and medulla in the brain of the blowfly Calliphora vicina, and investigated both temporal and spatial properties of the light-adapted cell. The sustaining unit fails to follow the highest temporal frequencies followed by the photoreceptor, but its temporal resolution is substantially better than that of the on-off unit. The sustaining unit does not display the fast temporal adaptation as previously described in the on-off unit. As compared with the on-off unit, the sustaining unit has a high sensitivity to small contrasts. Although the sustaining unit continues spiking as long as the light is on, its response is also transient as it adapts rapidly after a change of intensity. The receptive field and the line spread function of the sustaining unit have a similar size and profile: a central lobe with a half-width of approximately 2° surrounded by a circular inhibitory zone located at about 3° off-axis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192977
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  • 6
    Electronic Resource
    Electronic Resource
    Angular sensitivity of blowfly photoreceptors: intracellular measurements and wave-optical predictions (1984)
    Springer
    Journal of comparative physiology 155 (1984), S. 239-247 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The angular sensitivity of blowfly photoreceptors was measured in detail at wavelengthsλ=355, 494 and 588 nm. 2. The measured curves often showed numerous sidebands, indicating the importance of diffraction by the facet lens. 3. The shape of the angular sensitivity profile is dependent on wavelength. The main peak of the angular sensitivities at the shorter wavelengths was flattened. This phenomenon as well as the overall shape of the main peak can be quantitatively described by a wave-optical theory using realistic values for the optical parameters of the lensphotoreceptor system. 4. At a constant response level of 6 mV (almost dark adapted), the visual acuity of the peripheral cells R1-6 is at longer wavelengths mainly diffraction limited, while at shorter wavelengths the visual acuity is limited by the waveguide properties of the rhabdomere. 5. Closure of the pupil narrows the angular sensitivity profile at the shorter wavelengths. This effect can be fully described by assuming that the intracellular pupil progressively absorbs light from the higher order modes. 6. In light-adapted cells R1-6 the visual acuity is mainly diffraction limited at all wavelengths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00612641
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  • 7
    Electronic Resource
    Electronic Resource
    Electrical coupling of neuro-ommatidial photoreceptor cells in the blowfly (1986)
    Springer
    Journal of comparative physiology 158 (1986), S. 795-811 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A new method of microstimulation of the blowfly eye using corneal neutralization was applied to the 6 peripheral photoreceptor cells (R1–R6) connected to one neuro-ommatidium (and thus looking into the same direction), whilst the receptor potential of a dark-adapted photoreceptor cell was recorded by means of an intracellular microelectrode. Stimulation of the photoreceptor cells not impaled elicited responses in the recorded cell of about 20% of the response elicited when stimulating the recorded cell. This is probably caused by gap junctions recently found between the axon terminals of these cells. Stimulation of all 6 cells together yielded responses that were larger and longer than those obtained with stimulation of just the recorded cell, and intensity-response curves that deviated more strongly from linearity. Evidence is presented that the resistance of the axon terminal of the photoreceptor cells quickly drops in response to a light flash, depending on the light intensity. Incorporating the cable properties of the cell body and the axon, the resistance of the gap junctions, and the (adapting) terminal resistance, a theoretical model is presented that explains the measurements well. Finally, it is argued that the gap junctions between the photoreceptor cells may effectively uncouple the synaptic responses of the cells by counteracting the influence of field potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01324822
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  • 8
    Electronic Resource
    Electronic Resource
    The bright zone, a specialized dorsal eye region in the male blowflyChrysomyia megacephala (1989)
    Springer
    Journal of comparative physiology 164 (1989), S. 297-308 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. In the compound eye of the maleChrysomyia megacephala the facets in the ventral part of the eye are only ca. 20 μm in diameter, but increase abruptly to ca. 80 μm above the equator of the eye. Correspondingly there is a large and abrupt increase in the rhabdomere diameter from 2 to as much as 5 urn. The far-field radiation pattern of the eye shows that, despite the large change in ommatidial dimensions, the resolution of the eye remains approximately constant across the equator: angular sensitivity of the photoreceptors and sampling raster are similar ventrally and dorsally. The main result of the large dorsal facets is a more than tenfold increase in light capture. Thus this eye provides a clear example of an insect where large dorsal facets have evolved not for higher acuity, but rather for higher light capture. 2. Sensitivity is increased even more by a seventh photoreceptor cell joining neural superposition, as reported before for the dorsal eye of male houseflies. All seven photoreceptors have the same spectral sensitivity. 3. Angular sensitivities in the dorsal eye are more Gaussian-shaped than the flat-topped profile expected for large rhabdomere diameters. This is explained by the anatomical finding that the dorsal rhabdomeres taper strongly. It is suggested that the combination of high photon capture and rounded angular sensitivities is advantageous for monitoring movement and position of small objects. 4. Finally some of the constraints involved in constructing specialized dorsal eye regions for detection of small objects are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00612990
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  • 9
    Electronic Resource
    Electronic Resource
    On-off units in the first optic chiasm of the blowfly II. Spatial properties (1993)
    Springer
    Journal of comparative physiology 172 (1993), S. 467-471 
    Details
    ISSN: 1432-1351
    Keywords: Blowfly ; On-off unit ; Lamina ; Spatial processing ; Ganglion cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We recorded from the spiking on-off unit in the first optic chiasm (between lamina and medulla) in the blowfly Calliphora vicina, and investigated its spatial properties. The receptive field extends over (11.4±0.9)° horizontally and (8.7±0.6)° vertically, i.e. about 7 by 5 interommatidial angles. The line spread function of the on-off unit — calculated from its response to moving sinusoidal gratings — has a half-width of (2.3±0.2)°. This half-width is slightly broader than that of the photoreceptor. Lateral inhibition occurs when two different areas of the receptive field are stimulated simultaneously. Fast temporal adaptation (i.e. adaptation to trains of short light pulses) takes place independently in different areas of the receptive field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00213528
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  • 10
    Electronic Resource
    Electronic Resource
    Neural superposition and oscillations in the eye of the blowfly (1987)
    Springer
    Journal of comparative physiology 161 (1987), S. 849-855 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Neural superposition in the eye of the blowflyCalliphora erythrocephala was investigated by stimulating single photoreceptors using corneal neutralization through water immersion. Responses in Large Monopolar Cells (LMCs) in the lamina were measured, while stimulating one or more of the six photoreceptors connected to the LMC. Responses to flashes of low light intensity on individual photoreceptors add approximately linearly at the LMC. Higher intensity light flashes produce a maximum LMC response to illumination of single photoreceptors which is about half the maximum response to simultaneous illumination of the six connecting photoreceptors. This observation indicates that a saturation can occur at a stage of synaptic transmission which precedes the change in the post-synaptic membrane potential. 2. Stimulation of single photoreceptors yields high frequency oscillations (about 200 Hz) in the LMC potential, much larger in amplitude than produced by simultaneous stimulation of the six photoreceptors connected to the LMC. It is discussed that these oscillations also arise from a mechanism that precedes the change in the post-synaptic membrane potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00610226
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