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Introduction
Introduction
Pages 1-13
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From page 1... ...
Of great importance, also, even in a child who has learned to read, are the ease of reading and the pleasure afforded by the reading process when correctly and efficiently learned and the rewards that it brings by way of achievement. Motivation to read and extend one's knowledge is crucial in the acquisition of education, culture, and general enlightenment.
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From page 2... ...
per line, affording tachistoscopic exposures during which the span of apprehension permits intake and processing of information, provided that attention is maintained. At some level of the visual system, either in the retina or farther along in the visual pathways of the brain, suppression or inhibition of input apparently occurs during the intervening eye movements, inasmuch as no smearing or blurring of the type is apparent during the course of scansion of each line.
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From page 3... ...
; bipolar cells, which form synapses with cones and multisynaptic contacts with rods; and ganglion cells, which form synaptic contacts with bipolar cells. The axons of ganglion cells comprise the half-million fibers of the optic nerve in man.
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From page 5... ...
The light must also penetrate the layer of bipolar cells before it reaches the absorbing substances contained within the rods and cones, where photochemical processes occur. These reactions to light cause generator potentials to be built up in the receptor cells, thus initiating nerve impulses that are transmitted across the synapses between receptor cells and bipolar cells and then across the synapses between bipolar and ganglion cells.
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From page 6... ...
As the ciliary muscles attached to the ciliary body contract and reduce tension on the suspensory ligaments, the elastic properties of the lens allow it to bulge anteriorly; it thus has greater curvature and refracting power to bend light rays to a focus on the retina for a near-point fixation. When the eyes converge on a more distant point, the ciliary muscles relax, tension of the suspensory ligament is restored, and the lens tends to be flattened out, with less curvature and refracting power.
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From page 7... ...
When light activates the retina and generates impulses in the optic nerve and optic tract, most of these neural messages pass to the lateral geniculate nucleus in the thalamus and thence via the optic radiations to the primary visual cortex (area 17) along the striate area of the medial surface and the tip of the occipital lobe.
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From page 8... ...
Finally, because it has particular relevance to Sperry's paper, attention is drawn to how the nasal and temporal halves of the retina receive stimuli from the temporal and nasal halves, respectively, of the visual environmental fields. The optic nerve fibers from the nasal halves of each retina cross to the opposite sides in the optic chiasm and in the optic tract join the fibers coming from the temporal half of each retina.
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From page 9... ...
cut through the optic chiasm would eliminate the temporal visual fields for both eyes by inactivating the pathways leading to the visual cortex from the nasal half of each retina. Argument still prevails as to whether and how the central area of the fovea divides its input to the two halves of the brain, or whether the fovea centralis is bilaterally represented in the visual cortex of both hemispheres.
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From page 10... ...
The latter patients used the two hemispheres equally, often apparently without bias due to hereditarily or environmentally determined dominant hemispheric tendency; the hemispheres tended to have equivalent perceptual response patterns when tested separately, that is, by limiting input to one side or the other. By contrast, the group with section of the corpus callosum showed more complete visual perceptual performance for the dominant hemisphere than was possible with the nondominant hemisphere, but the minor hemisphere seemed to handle some nonvisual performances that the major hemisphere did not.
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From page 11... ...
Young proposes several refinements in the measurement of visual acuity and related optical characteristics of the eye. He believes that experimental studies in animals and man can be considered adequate for making evaluations only when several of these measures have been carefully applied and that the likelihood that children will experience visual difficulty due to optical causes in connection with reading can be appraised only when adequate assessment of schoolchildren is made by some of these methods.
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From page 12... ...
Several papers consider the effects of early experience and learning on visual information processing, conditions that tend to vary from individual to individual, in contrast with the visual mechanisms related to receiving, channeling, organizing, and storing, which are relatively constant for all individuals. Riesen discusses the effects of various types of visual environments on the functioning of the retina itself, and Flom discusses ways in which experience influences the visual behavior of the developing infant and also considers the role of early environment on the development of anomalous visual behavior.
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From page 13... ...
Finally, the patterns of development of visual information processing during the first year of life are discussed by Kagan. In addition to the panel discussion on the relationship between various factors involved in visual information processing and reading, three papers specifically relate various types of reading disabilities to the normal processing of visual information.
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