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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 53 (1983), S. 142-150 
    ISSN: 1432-1106
    Keywords: Oblique effect ; Vertical effect ; Meridional amblyopia ; Animal psychophysics ; Monkeys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Orientation anisotropies were investigated for monkeys with normal visual acuity and for monkeys with experimentally induced amblyopia. It was found that the majority of control monkeys showed a normal oblique effect if any existing refractive errors were carefully corrected, but a few of the control monkeys had a meridional amblyopia, i.e., an orientation anisotropy in which the grating orientation for the greatest and lowest contrast sensitivities were correlated with the principal meridians of an astigmatic refractive error even when the refractive error was corrected. For monkeys with strabismic amblyopia caused by a surgically induced divergent strabismus, the orientation anisotropies showed a vertical effect in which contrast sensitivity was lower for vertically oriented gratings than for horizontally oriented gratings. However, monkeys with the same degree of amblyopia resulting from experimental procedures that did not involve a misalignment of the visual axes showed orientation anisotropies that corresponded to the usual oblique effect.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1106
    Keywords: Amblyopia ; Stimulus deprivation ; Reverse deprivation ; Lateral geniculate nucleus ; Striate cortex ; Cytochrome oxidase ; Rhesus monkey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Monkeys had one eye closed at about 30 days of age for 14, 30, 60, or 90 days, then opened, and the fellow eye closed for another 120 days. The animals then had at least 10 months of binocular visual experience before extensive behavioral training and testing were carried out. In terminal experiments concluded more than 18 months later, microelectrode investigations of the striate cortex demonstrated that there was almost a complete absence of binocular neurons in all animals. The initially deprived eyes (IDEs) dominated the majority of cortical neurons, even when soma size measurements of lateral geniculate neurons indicated that the LGN cells driven by the IDE had not regained their normal size. The monkeys which had significant interocular differences in spatial vision also exhibited abnormalities in the distribution of the metabolic enzyme, cytochrome oxidase (CO), within the striate cortex. These results demonstrate that many of the severe alterations in cortical physiology and eye dominance produced by early monocular form deprivation can be reversed, with recovery of normal cortical function, via the reverse-deprivation procedure.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 80 (1990), S. 441-445 
    ISSN: 1432-1106
    Keywords: Lateral geniculate nucleus ; Visual cortex ; Receptive field ; Spatial phase ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We recorded single neuron responses in the cat's lateral geniculate nucleus (LGN) and visual cortex to compound stimuli composed of two sinusoidal gratings in a 2∶1 frequency ratio. To probe visual receptive field symmetry, we varied the relative spatial phase of the two components and measured the effect on neuronal responses. We expected that on-center LGN neurons would respond best to gratings combined in positive cosine (bright bar) phase, while off-center LGN neurons would respond best to gratings combined in negative cosine (dark bar) phase. When drifting stimuli were used, cells' phase preferences were roughly 90 deg away from the expected values; when stationary, contrast-modulated stimuli were used, phase preferences were as originally predicted. Computer simulations showed that this discrepancy could be explained by taking into account the cells' temporal properties. Thus, tests using drifting stimuli confound the spatial structure of visual neural receptive fields with their temporal response characteristics. A small sample of data from cortical neurons reveals the same confound.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 39 (1980), S. 351-356 
    ISSN: 1432-1106
    Keywords: Oblique effect ; Meridional amblyopia ; Contrast sensitivity ; Animal psychophysics ; Reaction time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Contrast sensitivity as a function of the orientation of a grating stimulus was determined by behavioral methods for four rhesus monkeys. Two of the monkeys had been reared with normal binocular experience, had spherical refractive errors, and showed a normal oblique effect. The other two monkeys which had been reared with one eyelid sutured (which was still sutured during these experiments), showed astigmatic refractive errors in the non-deprived eye and grating contrast sensitivity as a function of orientation that was correlated with the principal meridians of their astigmatism. Control experiments showed that the meridional amblyopia was not due to an uncorrected refractive error. Reaction time measures of contrast sensitivity for suprathreshold grating patterns showed that meridional amblyopia was not present for high contrast gratings.
    Type of Medium: Electronic Resource
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