The role of inhibition in the development of pattern vision in human infants.
Item
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Title
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The role of inhibition in the development of pattern vision in human infants.
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Identifier
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AAI3296945
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identifier
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3296945
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Creator
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Garcia-Quispe, Leticia A.
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Contributor
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Adviser: James Gordon
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Date
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2008
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Neuroscience | Psychology, Psychobiology
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Abstract
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There are major developmental changes in the visual system early in infancy which continue throughout childhood and possibly even later. The purpose of this study is to describe the development of cortical responses to gratings of different contrasts and spatial frequencies in order to characterize the neural mechanisms that contribute to these responses. In spatial tuning functions from infants we examined the changes in the low spatial frequency limb of the function, the peak of the amplitude and the acuity limit, as well as differences between the eyes. In the contrast response functions, we obtained representative data from infants in order to quantify amplitude and phase functions using a nonlinear model based on shunting inhibition. The model generates estimates of shunting inhibition and integrative time constants in the visual system.;The stimuli were horizontal square-wave gratings contrast-reversed at 7.5 Hz. For spatial tuning functions, spatial frequency was swept in six octave steps from 0.8 c/deg to 24 c/deg in infants (1.6 c/deg to 48 c/deg in adults). Five or ten runs were obtained from each participant (6.4 s each). For the contrast response functions, gratings of 0.75 c/deg or 1.5 c/deg were used, and contrast was swept in eight octave steps from 0 to 64%. Ten runs were obtained (8.5 s each). Infants from 10 through 31 weeks of age were tested. Some children and adults were tested for comparison. The amplitude and phase of the second harmonic were computed and plotted versus spatial frequency or contrast.;The results indicate that in general, infants' spatial functions have a less pronounced low-spatial frequency fall-off, their amplitudes tend to be larger, the peak of their functions is at lower spatial frequencies, and they have lower acuities than adults. Infants show slight but adults show steep phase lags with increasing spatial frequency. Most infants had well-matched right versus left eye responses (a significant difference at one spatial frequency or none). In general, contrast response functions in infants are more linear with increases in contrast, and they do not show amplitude saturation. Infant phases are relatively flat whereas adult phases advance with increases in contrast. Adults show high contrast gain control (amplitude compression and phase advance) but it is lacking or weakly present in most infants. In general, infants have longer time constants than adults, and time constants decrease with increasing contrast. These results are consistent with greater inhibitory cortical activity (lateral inhibition and shunting inhibition) in adults than in infants.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
