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  • 1975-1979  (2)
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  • 1
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The development of orientation selectivity in the primary visual cortex is described by first-order kinetics between three functional compartments chained in a catenary mode. A first model is presented, in which two unidirectional kinetics with constant exchange coefficients, symmetrical in their effects, function in an alternating mode depending on the presence or absence of visual experience. The failure of this model to simulate the modifications induced by a delayed visual experience, when the exchange coefficients are identified to fit normal and dark rearing, supports the hypothesis that the maturation process consequent to interaction with visual environment is dependent on the date at which it is allowed to take place. A second model is then proposed, in which exchange coefficients are piecewise linear functions of time. In order to correctly predict the functional effects of restricted visual experience following prior dark rearing, it is assumed that visuomotor experience during the critical period permits the expression of a non-linear “modifiability gradient” which may have been masked up to this point by the absence of vision or eye movements.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Kinetics of the development of orientation tuning are inferred from quantitative analysis of extracellular recordings in the primary visual cortex of normally and dark reared kittens. 712 visual cells were classified in three functional groups: a) non-specific cells, and b) immature cells which are not as orientation selective as c) specific cells. Power regression and covariance analysis indicate that the “critical period” begins before 19 days and that the kinetics of the immature pool are the same in both rearing conditions. A catenary process of development of orientation selectivity is proposed, the immature compartment being a transit pool between non-specific and specific cells. Two sequential stages occur: 1) the realisation of an intrinsic programme of maturation, by which cortical specificity appears at eye opening and increases independently of visual experience 2) a phase of “epigenesis” beginning at 19 days, during which functional modification depends on visual experience.
    Type of Medium: Electronic Resource
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