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  • 1
    Electronic Resource
    Electronic Resource
    The role of transferrin-receptor variation in the host range of Trypanosoma brucei (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 391 (1998), S. 499-502 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Trypanosoma brucei is a unicellular parasite transmitted between African mammals by tsetse flies. T. brucei multiplies freely in the bloodstream of many different mammals, and survives by antigenic variation of the main component of its surface coat, variant surface glycoprotein (VSG),. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35166
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  • 2
    Electronic Resource
    Electronic Resource
    Differences in peripheral and foveal effects observed in stabilized vision (1978)
    Springer
    Experimental brain research 32 (1978), S. 225-243 
    Details
    ISSN: 1432-1106
    Keywords: Stablized images ; Perceptive elements ; Fading time ; Foveal activity ; Filling-in
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Foveal images fade much faster than peripheral images, at light-on as well as at light-off. An opposite result can be obtained, however, in case of unsatisfactory stabilization. The amount and extension of the brightness spreading before the fading depend on the stimulus brightness and its location on the retina. The intensity threshold and the maximal obtainable sharpness of the image decrease towards the periphery, the image becomes wider and sharper on increasing the stimulus intensity. In the foveal area brightness or darkness can be observed (even from stimuli below the foveal threshold) by a filling-in from the periphery, which has a lower threshold. On increasing the stimulus intensity very small pinpoints of light, tiny dots are observable in the foveal area. Each dot measures less than 1 min arc in diameter and is visible for a few hundred milliseconds only. The final sharply contoured foveal percept of a narrow line, observed at higher intensities, is made up of a crowding of these tiny dots. When lines wider than about 10 min arc are used as stimuli these small foveal dots are only seen along the inside contours but not on the (diffuse) interior of the line. In the periphery no tiny dots but only spots of larger size can be observed. At each location of the visual field the final percept seems to be built up from the co-operation of a number of perceptive elements of different sizes. Small elements fade faster, have higher thresholds, habituate more easily on repeated stimulation and become easier activated by small-amplitude stimulus displacements than larger elements. The results described, contradicting some literature data, depend heavily on the quality of the stabilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239729
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  • 3
    Electronic Resource
    Electronic Resource
    Apparent movements induced by stroboscopic illumination of stabilized images (1979)
    Springer
    Experimental brain research 34 (1979), S. 471-488 
    Details
    ISSN: 1432-1106
    Keywords: Temporal modulation ; Stabilized images ; Habituation ; Perceptive elements ; Barriers ; Filling-in
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Stroboscopic illumination of stabilized images causes habituation effects and illusory phenomena which, at low stimulation frequencies, show up as brighter patches. When a line is used as a stimulus, these patches are observed as brighter spots in the line surrounded by dimmer patches in the background. These locally brighter parts function as sources from which brightness spreads in the direction of the line at light-on and as sinks to which the brightness retracts again after light-off. This spread and retraction of the brightness induces the perception of movements. Higher stimulation frequencies or a diminished stimulus-background contrast enables the brightness to spread also in the direction perpendicular to the line contour, i.e., into the background. Again a perception of movement is induced, local displacements of a part of the field are observed as a result of the brightness spread. Tiny pinpoints of light, the smallest foveal perceptive elements, visible in lines narrower than 10 min arc (Gerrits, 1978), are also observed when these lines are illuminated with Stroboscopic light. These tiny elements do not spread their brightnesses and so also no movement is induced. The results are discussed in relation to the properties of the perceptive elements and the cells activating them (habituation, barriers, filling-in).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239143
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  • 4
    Electronic Resource
    Electronic Resource
    Afterimages: a collective term for percepts of different origin (1988)
    Springer
    Experimental brain research 72 (1988), S. 279-286 
    Details
    ISSN: 1432-1106
    Keywords: Afterimage ; Intensitivity percepts ; Filling-in ; Receptive fields
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Exposure of the eye to a strong photoflash results in a so-called “afterimage”, which may last for 20 min or longer. In contrast, the true afterimage, which fluctuates in brightness and is best seen in complete darkness, lasts only a few minutes. This true afterimage can be attributed to the strong oscillatory neuronal responses immediately initiated by the flash. Thereafter dark and light regions, insensitivity percepts, are observable against bright and dark backgrounds, respectively. These percepts can be adequately explained by a reversal of the response behaviour of rod and cone driven ganglion cells situated along the contour of the flash-exposed area. The slow recovery of the rods explains why insensitivity percepts can be seen for many minutes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00250250
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  • 5
    Electronic Resource
    Electronic Resource
    Simultaneous contrast, filling-in process and information processing in man's visual system (1970)
    Springer
    Experimental brain research 11 (1970), S. 411-430 
    Details
    ISSN: 1432-1106
    Keywords: Simultaneous contrast ; Filling-in ; Scotomata ; Correlation with on-center and off-center cells ; Stabilized image disappearance ; Brightness perception
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In psychophysical experiments described previously we found that a stimulus surrounding a retinal scotoma fills in the scotoma instantaneously with its brightness and color. However, it takes a few seconds to fill in a black stabilized disk which is equally immobile with respect to the retina. An experiment carried out to investigate the cause of this discrepancy suggested that a presumed contrast firing of neurons along the inside border of the black stabilized disk may explain the phenomena. The postulated border contrast discharge may form a barrier for the spreading of brightness information from the surround. If no barrier is generated (as in retinal scotomata) or if it has disappeared (by stabilization) the spreading of the activity itself occurs very rapidly (probably in higher centers). The co-operation of these effects, the activity along the border of a field (the simultaneous contrast) and the filling-in, investigated in the experiments, may explain many perceptual phenomena. A model is proposed which is based upon stabilization experiments, neuronal recordings of other authors and reports from patients with defective visual systems. The well-known first stages (retina-lateral geniculate body-area 17) and a following, yet unlocalized, stage (called “higher center”) are distinguished. Stabilization experiments suggest a spreading capacity and a long adaptation time of this higher center. The spreading of activity is inferred clinically and from observation of the filling-in phenomenon. Long adaptation time is suggested by the slow disappearance of the stabilized image. In normal vision small eye movements, continually activating on-center cells and off-center cells along the contrast border preserve continuous perception of the whole homogeneously illuminated area from transient border activities. Neuronal mechanisms and a model of antagonistic barriers and mutual neutralization are discussed and indicated in a diagram.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00237914
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  • 6
    Electronic Resource
    Electronic Resource
    The filling-in phenomenon in vision and McIlwain's periphery effect (1974)
    Springer
    Experimental brain research 19 (1974), S. 343-350 
    Details
    ISSN: 1432-1106
    Keywords: Optic tract ; Periphery effect ; Filling-in
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The change of activity of optic tract fibers of the cat has been measured when moving visual stimuli are presented at a large distance from the center of the receptive field (McIlwain's periphery effect). Two different patterns of moving visual stimuli are used. The effects of the same stimuli are studied psychophysically with stabilized images. It appears that the peripheral stimulus which is most effective in eliciting the periphery effect in the electrophysiological experiments does not cause the filling-in phenomenon in the psychophysical experiments, whereas on the other hand a stimulus which causes a psychophysically clearly observed filling-in phenomenon generates a very small periphery effect in the electrophysiological experiments. The conclusion is that, although some spread of activity over large distances in the retina exists, this spread is not correlated with the perception of the filling-in. These findings can be explained on the basis of a model of the information processing in the visual system, derived from experiments with stabilized images.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234459
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  • 7
    Electronic Resource
    Electronic Resource
    Analysis of the response characteristics of optic tract and geniculate units and their mutual relationship (1972)
    Springer
    Experimental brain research 15 (1972), S. 452-471 
    Details
    ISSN: 1432-1106
    Keywords: Optic tract ; Lateral geniculate nucleus ; Transfer characteristics ; Intrageniculate inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Responses to light stimuli of cat's optic tract and geniculate units are analyzed. Characteristics originating from the center and the surround of the receptive field are traced. These characteristics differ between ON-and OFF-center units. The origin of these differences is discussed. 2. Transfer characteristics of geniculate neurons have been determined by comparing the responses of optic tract and geniculate units. The main difference between these responses consists of a decreased responsiveness of the geniculate neurons. This is due to the fact that most recordings were made when the cat was asleep. During wakefulness the geniculate responses approximate most to the optic tract responses. Some other differences include an increase of inhibition in some periods of the LGN response. The firing pause of the ON-center geniculate neurons after the first excitation in particular is a characteristic feature of these neurons. 3. It is also possible to determine the input of geniculate neurons from the postsynaptic potentials visible in the quasi-intracellular recordings. Input-output relationships of these neurons confirm the differences mentioned above. These recordings show that the increase of inhibition is caused by intrageniculate hyperpolarizations. 4. It is generally accepted that the hyperpolarizations are mediated by the interneurons present in the LGN. Strong evidence exists that the input of these interneurons originates both from ON-center and OFF-center units as suggested by Burke and Sefton (1966a, b, c). Whether forward (optic tract) or backward (LGN) fibres project to these interneurons is not completely clear. Arguments for the existence of both types of projections are given. The function of this intrageniculate inhibition is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236402
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  • 8
    Electronic Resource
    Electronic Resource
    Characteristics of the transactivator gene ie1 of Spodoptera exigua multiple nucleopolyhedrovirus (2000)
    Springer
    Archives of virology 145 (2000), S. 2115-2133 
    Details
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary.  The genomic position and nucleotide sequence of the immediate early gene ie1 of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) were determined. The SeMNPV ie1 gene had the potential to encode a protein of 714 amino acids with a predicted molecular mass of 82.0 kDa, representing the largest baculovirus IE1 known to date. The similarity of SeMNPV IE1 with IE1 proteins from other baculoviruses was restricted to the basic C-terminal two-thirds of the protein, which is involved in DNA binding. A single ie1 transcript of 2.5 kb was detected at 1 h p.i., peaking at 8 h p.i. and disappearing at 24 h p.i. From 8 h p.i. onwards a 1.7 kb transcript was detected, which became more abundant late in infection. Primer extension analysis revealed the use of several start sites early and late in infection. One of these was located in the promoter motif CAGT located at position −15 relative to the translational start codon, most intensively used at 8 h p.i. Four kb upstream of the SeMNPV ie1 gene, ORF xd244 was identified with homology to the used left ie0 exon of AcMNPV, OpMNPV and LdMNPV. Phylogenetic analysis indicated that the SeMNPV IE1 protein shared the most recent ancestor with its HzSNPV and LdMNPV homologues, although their IE1 proteins had diverged considerably from each other and from other baculoviruses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007050070043
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