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Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
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Page 1
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 2
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 3
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 4
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 5
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 6
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 7
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 8
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 9
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 10
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 11
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 12
Suggested Citation:"Introduction." National Research Council. 1970. Early Experience and Visual Information Processing in Perceptual and Reading Disorders: Proceedings of a Conference Held October 27-30, 1968, at Lake Mohonk, New York, in Association With the Committee on Brain Sciences, Division of Medical Sciences, National Research Council. Edited. Washington, DC: The National Academies Press. doi: 10.17226/18684.
×
Page 13

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DONALD B.LINDSLEY / FRANCIS A. YOUNG Introduction The principal means of acquiring and accumulating information is through the printed word or symbol. To optimize the use of printed information through a progressive learning process, it is necessary for a child not only to learn to read, but to gradually develop a high degree of skill, speed, and efficiency in reading. Some children, known as nonreaders, never learn to read. Others learn to read, but only very slowly, with great difficulty, and inefficiently, thus impairing their acquisition of knowledge during the school years and throughout life. Still others learn to read on schedule, but with varying degrees of skill and efficiency, as measured in terms of speed of reading, comprehension, ability to select information and process it into memory storage, and ability to retrieve information from short- or long- term storage and use it for concept formation, thinking, and problem- solving. 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 gen- eral enlightenment. It should be evident that reading, which, once learned, seems like

DONALD B. LINDSLEY / FRANCIS A. YOUNG such a simple process, is indeed a complicated aspect of a broader information-processing function, including perception and higher cogni- tive processes. The ability to see and read printed words depends on the qualities of the physical stimulus (e.g., illumination, visibility, contrast), the form and pattern of the printed elements (letters, words, sequences of words, and so on), and, of course, knowledge or understanding of the language of which the words are symbols. In addition, the eyes must be trained to scan the stationary stimulus patterns provided by the printed text in a series of stop-and-go movements, usually two or three fixations (saccadic eye movements) 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 ap- parently occurs during the intervening eye movements, inasmuch as no smearing or blurring of the type is apparent during the course of scan- sion of each line. Likewise, the adjacent portions of other lines, although within the visual field of each fixation, are somehow suppressed, pos- sibly by selective attention to the line being read. These are just a few of the aspects of the process of reading with which the conference was concerned. In planning the conference, it was recog- nized that there is a great deal of basic information about vision and visual perception and that in recent years much new information has been acquired about the mechanisms of the eye and the brain that has not been brought to the attention of those concerned with applied prob- lems in which these mechanisms are involved. Furthermore, consider- able effort has been expended in a search for the onset and develop- ment of various psychologic and behavioral functions, as well as their anatomic and physiologic precursors. In some instances, deliberate inter- ference with or blocking of development of functions has been attempted in young animals. In others, manipulation of the environment, either in the form of sensory deprivation or restriction or in the form of enrich- ment and enhancement of stimulation, has been studied, with the aim of determining how these changes affect the developing and maturing organism. To provide an orientation toward reading behavior, Jeanne Chall re- views the philosophies and methods that have been used during the last 40 years in the teaching and assessment of reading skills. Trends in the teaching of reading have gone full circle from a "decoding emphasis"—

Introduction first learning the alphabet and the composition of words—to "meaning emphasis"—largely ignoring the alphabet and syllable approach and con- centrating on the meanings of words and phrase patterns as wholes. Dur- ing the last decade, the more innovative approaches have shown a swing back to decoding emphasis, to be followed when appropriate by mean- ing emphasis. Although the results of her study seemed to favor this ap- proach, she cautiously states that the evidence is by no means clear-cut. Dr. Chall's presentation emphasizes the importance of periodic con- ferences of this kind in extending the knowledge of reading and reading disorders and providing bases for decisions. It also highlights the too common failure of basic scientists to realize the extent to which their own somewhat specialized research may have important implications for educators and practitioners. The initial papers are concerned with the role of the visual system in information processing, starting with the more peripheral aspects—those involving the eye—and moving along the visual pathways to the visual cortex. Because the nonspecialist may not be familiar with the visual process, a description of how the image is formed and what happens to the nerve impulses generated is presented here. Figure 1 is a schematic illustration of the general features of the visual system. The eye is essentially a spherical body, except for the slight bulge at its anterior surface provided by the cornea, the exposed part of the eye. The lateral and posterior walls of the eyeball consist of the sclera, a tough outer membrane that serves as a protective and restrain- ing covering for the contents of the eye, which are under pressure greater than that of the atmosphere. Inside the sclera is the deeply pigmented choroid, which contains the principal blood supply for the eye and pre- vents light from entering the eye through the sclera, thus preventing light scattering within the eye. Inside the choroid is the retina, contain- ing the receptor elements (rods and cones); 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. Also within the retina are important multiconnector cells (horizontal and amacrine), some cells thought to serve integrative and summative functions, and others thought to serve the role of lateral inhibition and excitation, which are important to image contrast in the retina and to on- and off-center receptive fields. The rods and cones are next to the choroid.

DONALD B. LINDSLEY / FRANCIS A. YOUNG CORNEA IRIS CILIARY BODY LENS OPTIC CHIASM OPTIC TRACT ANTERIOR COMMISSURE THALAMUS LAT. GENICULATE NUCLEUS SUP. COLLICULUS OPTOMOTOR NUCLEI CORPUS CALLOSUM VISUAL CORTEX FIGURE 1 Diagram of human visual system, showing visual fields and pathways.

Introduction Light penetrates the cornea and passes through the pupil, which is formed by the iris. The iris, through the action of its circular and radial muscular coats, regulates the size of the pupil and the amount of light entering the eye. The entering light is refracted or bent primarily at the air-cornea interface and slightly at the interface with the aqueous humor of the anterior chamber immediately behind the cornea. Following the major refractive effect of the cornea, the lens, whose curvature increases when the suspensory ligaments that encompass it are relaxed by action of the muscles of the ciliary body, provides the second most important refractive effect on the light rays. Light continues through the gel-like vitreous humor filling the posterior two thirds of the eyeball and then passes through the layer of ganglion cells and their axons, which leave the eye through the optic disk (blind spot) to form the optic nerve. The light must also penetrate the layer of bipolar cells before it reaches the absorbing substances contained within the rods and cones, where photo- chemical processes occur. These reactions to light cause generator poten- tials to be built up in the receptor cells, thus initiating nerve impulses that are transmitted across the synapses between receptor cells and bi- polar cells and then across the synapses between bipolar and ganglion cells. Horizontal and amacrine cells play a role in regulating the flow of impulses through these retinal paths to the optic nerve. For the most part, light that escapes the retinal receptors is absorbed by the heavily pigmented choroid. A schematic illustration of neuroretinal components is provided in the paper by Boynton (Figure 8, p. 107); histologic sec- tions of the retina are reproduced in Glickstein's paper. The optical apparatus of the eye needs physical and dynamically func- tional characteristics for bringing patterned rays of light into proper focus on the sensitive and labile photographic screen known as the ret- ina. Typically, if a point source is to be seen clearly at reading distance, accommodation must occur and the eyes must converge (as described below) in order to bring the image of the point onto the fovea (the por- tion of the retina at the back of the eyeball where only cones are found). At the same time, pupillary constriction limits the exposed lens to its region of greatest curvature and least aberration. The high density of cone receptors in the fovea and their essentially one-to-one relationship to bipolar and ganglion cells affords a high resolution of the image pro- jected on the foveal retina. If light were focused parafoveally or on the peripheral retina, fine discrimination and high-acuity resolution would not be possible. Such a situation may arise in the case of strabismus or

DONALD B. LINDSLEY / FRANCIS A. YOUNG "squint," described in Alpern's paper, if the muscles of the eyes are in- adequate to maintain proper convergence alignment, so that the images in the two eyes are not formed on corresponding retinal points. In nor- mal eyes, the two images are formed on corresponding retinal points, and the slightly different views of an object give rise to the stereoscopic effect of depth. However, with respect to most plane surfaces, the image formed on the retina of the nondominant eye is partially (sometimes wholly) suppressed in favor of the dominant eye. This suppression may be demonstrated by holding a finger at arm's length and looking over its tip binocularly at the wall beyond; when the right eye (if dominant) is closed, the view with the left eye shifts markedly to the right, wheveas, if the left eye is closed, the view remains the same as when seen binocu- larly. Visual accommodation is the process by which the lens of the eye ad- justs to focus light from a near object on the retina for near-point view- ing. 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 refract- ing 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. When either (or both) of these actions is no longer possible or when other characteristics of the eye change, making it impossible to bring light to a focus on the retina, corrective lenses are necessary. If light comes to a focus behind the retina, rather than on it, owing to lack of refractive power of the eye, a condition of hyperopia, or farsightedness, exists. In infancy, although the eye itself is small, the lens is nearly of adult size and thus contributes a greater portion of the total refraction of the eye than in the adult. In old age, the total refracting power of the lens is reduced by decreased elasticity, producing hyperopia, or farsighted- ness (presbyopia). Light focuses in front of the retina in nearsighted, or myopic, persons, who have no difficulty reading at near distances that would be difficult for a normal (emmetropic) eye. The power of a lens necessary to correct for improper focus on the retina is expressed in diopters, or the reciprocal of the focal length (given in meters). Thus, a concave (minus) lens with a focal length of-0.25 m would be 1/-0.25, or -4 diopters. Other aberrant properties of the optics of the eye that may lead to

Introduction difficulty in reading come under the heading of astigmatism. The curva- ture of the cornea or lens may be irregular in one or more dimensions, so that the image on the retina is clear in one place and fuzzy in another. During accommodation and convergence, the pupil constricts. All three of these actions are mediated by the third cranial nerve (oculo- motor); they occur in focusing on a line of type in reading and create a sharp image on corresponding points of the two retinas. In reading, the eye moves from left to right in quick saccadic jerks produced by the ex- ternal rectus muscle of the right eye and the internal rectus of the left eye, while the opposed recti of both eyes retain sufficient tension to cause proper convergence. A pair of muscles is also attached above and below the eyeball. These four symmetrically placed muscles control up and down and right and left movements of each eye. In addition, a pair of obliquely placed muscles rotates and tilts the eye downward or up- ward. Innervation of the external eye muscles is via the third, fourth, or sixth cranial nerve. It is believed that in voluntary and perhaps also involuntary eye movements motor discharges from the motor eye fields of the cortex (Brodmann's area 8) convey impulses to the region of the midbrain and pons. Thus, cortical control of eye movements is possible, but it is uncertain how much of a role the higher centers in the motor cortex play in the usual tracking movements of the eyes during reading, with frequent stop and go interactions. It seems more probable that tracking movements are mainly of reflex nature and are a function of retinal excitation and neural discharges feeding back to optomotor and pretectal nuclei. 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. A much smaller fraction of the impulses pass by way of the superior colliculus to the tectal region of the midbrain. In Figure 1, pathways along the superior colliculus are shown schematically as curved lines emanating from below the lateral geniculate nucleus and passing to the superior colliculus or pretectal nuclei, whence it is a short path to the optomotor nuclei and the reticu- lar formation of the lower brain stem. The reticular formation plays a role in arousal, activation, and attention; some investigators think that it also plays a role in learning and memory processing. Thus, in addition to the specific visual pathways via the lateral geniculate nucleus of the

DONALD B. LINDSLEY / FRANCIS A. YOUNG thalamus and optic radiations to the visual cortex, there are indirect or nonspecific pathways from the optic tract to the superior colliculus and pretectal nuclei of the midbrain. The latter undoubtedly constitute im- portant feedback pathways for the regulation of the optics of the eye and eye-movement control, and provide possible connections with the reticular formation of the lower brain stem, and possibly also with the pulvinar. The excitability of the cortex may be influenced through these nonspecific arousal and activation mechanisms. Thus, such indirect con- trol of cortical activities generally, and perhaps visual cortical activity specifically, may play a role in the degree to which attention is main- tained in reading and similar visual tasks. The nonspecific visual path- ways are described in detail in the paper by Buser. The lateral geniculate nucleus is organized as a six-layered structure, and a pattern of input from the two eyes comes to the lateral geniculate laminae in a partially alternating manner. The organizational relationship to function in the retina and geniculate is demonstrated in Glickstein's paper. The receptive-field concept, described in detail in the paper by Jung and Spillmann and first demonstrated in the retina, includes the idea that the field representation is partially retained and in some re- spects elaborated at the level of the lateral geniculate nucleus and the visual cortex. In the visual cortex, organizations of neuron units seem to represent simple, complex, and hypercomplex patterns of activation and functioning with respect to information presented to the retina. Some units respond to angular and linear stimulus arrays, others seem to respond only to movement, and so forth. Marg reports on some of these characteristics for single units of the human visual cortex. Finally, because it has particular relevance to Sperry's paper, atten- tion 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. Thus, the temporal half of the left retina and the nasal half of the right retina, each viewing part of the right-half nasal field for left eye and temporal field for the right eye of the field of view when the eyes are converged to a fixation point, send their messages via pathways to the left hemisphere of the brain (left visual cortex of the occipital lobe). Similarly, the nasal half of the retina in the left eye and the temporal half in the right eye send their messages via pathways to the right hemi- 8

Introduction sphere of the brain. A longitudinal (midsaggital) cut through the optic chiasm would eliminate the temporal visual fields for both eyes by inac- tivating 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. It is generally assumed that the left hemisphere of the brain in right- handed (and perhaps right-eyed) persons is the dominant or major hemi- sphere, whereas the right hemisphere is the nondominant or minor hemisphere. Objections to this assumption usually revolve around the determination of laterality or sidedness and whether hand or eye use is an adequate index of "native" or hereditary tendencies to unilateral hemisphere control or whether eye or hand use merely reflects the fact that we live in a world better adapted to the right-handed and right-eyed majority of people. For example, a typical school chair with a writing arm on the right is awkward for a left-handed person. There are many other examples of both unimanual objects and uniocular instruments built for the predominantly right-handed population. It is argued that such a dextrally organized world tends to prevent a hereditarily deter- mined preference for sinistrality from becoming a reality. It has fre- quently been observed that so-called right-handed children may have a native preference for the left that manifests itself on some unimanual or uniocular tests that are not biased by learning in favor of the right. Simi- larly, some left-handed children who were compelled to write with their right hands may have developed stuttering speech, illegible writing, or other aberrations. The tendency to read or write letters and words in reversed or mirror fashion appears in some children with reading dis- abilities. And there is much evidence that the controlling motor speech center (Broca's area) is situated in the dominant hemisphere, namely, in the left hemisphere of right-handed subjects. Damage to this area usually in- duces a motor aphasia, whereas damage to the homologous area of the nondominant hemisphere does not have this effect. Thus, for speech, there seems to be good evidence of unilaterality of control. Sperry's re- sults in contrasting the perceptual capabilities of patients with partially "split" brains, through section of the corpus callosum, after a lifetime of usage and orientation in which one hemisphere presumably dominated showed greater differential hemispheric effects and more profound

DONALD B. LINDSLEY / FRANCIS A. YOUNG deficits than in patients with agenesis of the corpus callosum. The latter patients used the two hemispheres equally, often apparently without bias due to hereditarily or environmentally determined dominant hemi- spheric 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 hemi- sphere, but the minor hemisphere seemed to handle some nonvisual per- formances that the major hemisphere did not. These results will, of course, have to be confirmed and extended, but they are important to concepts about the conflicting tendencies, with respect to both sensory input and motor outflow, that interfere with such processes as reading, writing, speaking, and, probably, general motor coordination in children or adults. There may also be important implications in this work for the estab- lishment early in life of sure laterality and hemispheric dominance. Once it is determined that a child is right- or left-handed and has a definitely dominant hemisphere for sensory input and motor outflow, there may be stimulus patterns or situations that should be reinforced if the domi- nance bias is to be retained and strengthened. There may even be charac- teristics of printed or written words that are not appropriate for persons with sinistral organization and dominance of the brain. This would seem to be true: the favored extensor usage of the arm in writing tends to favor the forward-moving (to the right) tendency of writing letters and words. That is to say, some letters—such as "d" and "q"—perhaps re- quire that the forward abduction (extensor) movement to the right be stopped in order to backtrack with an adductor (flexor) movement of the arm in making the bulge of the letter, whereas the writing of "p" or "b" seems mainly consistent with this direction of movement of the arm. More of our practiced movements with the arms, both reflex and voluntary, seem to involve extensor and abductor (push-away) move- ments than flexor and adductor movements. There is room for much more research in this field, and it seems apparent that such research will have relevance for speaking, reading, and writing, not to mention other functions that depend heavily on these basic modes of communicating and processing information. It is apparent that reading involves physical environmental stimuli whose potential informational value can be realized only if the visual 10

Introduction system is capable of carrying the load that it is presumed to carry. Its optical and oculomotor properties and characteristics must be properly functioning and understood to achieve optimal conditions for reading. Francis Young has studied several visual measuring methods in popu- lations living and working under environmental conditions that have in- fluenced the manner in which their eyes handle refractive problems. His data on nonhuman primates, Eskimos, and other people (both children and adults) appear to him quite compelling in showing that environment and usage of the eyes have strong influences on their optical character- istics. He reports that there are studies that favor hereditary determina- tion of optical characteristics of the eye and others that favor environ- mental influences, but that the evaluation methods are not always appropriate and the data in many cases have been obtained under an existing situation, rather than experimentally. Young proposes several refinements in the measurement of visual acuity and related optical characteristics of the eye. He believes that experimental studies in ani- mals 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. Schubert, whose contribution is closely related to that of Young, at- tempted to create myopia and astigmatism by the use of lenses and to study the effect on far-point perception when the stimuli were presented tachistoscopically. He concludes that this experimental approach dem- onstrates that students with relatively mild degrees of myopia or astig- matism are likely to be handicapped in the school situation, where rapid presentations of material at varied distances are involved. It would seem that further experimental studies, closely related to classroom condi- tions, would add valuable knowledge about visual requirements for stu- dents in the school situation, especially in relation to reading. Man's two eyes tend to work as a single unit because of their precisely coordinated movements. Cogan and Wurster discuss the development of the ocular motor control of the extraocular muscles that move the eyes. Assuming that a person has developed normal eye-movement patterns, how are these eye movements related to what is received in visual per- ception? This subject is discussed by Gaarder. With normal functioning of the individual eyes and coordinated func- tioning of the two eyes as a unit, the organism is ready to receive visual 11

DONALD B. LINDSLEY / FRANCIS A. YOUNG stimuli and to bring them to a focus on the retina itself. On the retina, however, there must be sufficient variation in brightness in the stimulus pattern to permit the observer to discriminate the pattern. Without dif- ferent levels of retinal contrast, all visual input would be uniform and consist mainly of evenly illuminated fields. The mechanisms underlying retinal contrast are discussed by Boynton. If the stimulus patterns over- lap, binocular interaction may momentarily suppress retinal sensitivity. Alpern relates this situation to the pupillary reflex to light in strabismus. Visual information reaching the brain is further processed by atten- tional and perceptual mechanisms in visual information processing. Doty discusses the various parts of the visual cortex and input areas of the nervous system that control input channeling and determine the charac- teristics of visual input, as far as the brain level is concerned. Sperry dis- cusses cerebral dominance and its major role in maturation of the indi- vidual's perceptual behavior. The papers mentioned previously deal with the characteristics of the visual input and the role of the nervous system in receiving and channel- ing the input. Turning now to attentional and perceptual mechanisms, the size of the visual receptive fields and the integration of perceptual phenomena to form a meaningful unit are discussed by Jung and Spill- mann. Marg's findings from single-unit recording in man are relevant here. The retention and storage of visual perceptual input and its modi- fication are the subjects of Sperling's paper, and he emphasizes the im- portance of scanning and rehearsal. Hochberg proposes that attention is an integral part of the reading process, and he explores the way in which the reader's knowledge affects paying attention. The importance of the relationship of language comprehension and use to reading ability is stressed by Hirsh. Several papers consider the effects of early experience and learning on visual information processing, conditions that tend to vary from individ- ual to individual, in contrast with the visual mechanisms related to re- ceiving, 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 develop- ing infant and also considers the role of early environment on the de- velopment of anomalous visual behavior. Fantz and Lipsitt discuss the development of pattern perception and the types of information-seeking that occur in early infancy. Hirsh considers, in the preceding section, 12

Introduction visual and auditory perception and language as they tend to be related in the development of reading behavior, which usually follows the devel- opment of language behavior. The effects of various types of social and environmental deprivations on the ability of the organism to handle visual input are discussed by Mason, and the specific effects occurring in the nervous system of various types of visual sensory deprivation are treated by Valverde and Ruiz-Marcos. 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 vari- ous factors involved in visual information processing and reading, three papers specifically relate various types of reading disabilities to the nor- mal processing of visual information. Ingram deals with the neurologic characteristics of persons exhibiting dyslexic behavior. Children with reading disabilities frequently have various types of disorganized visual perception; some of these disorganizations are discussed by Silver and Hagin. Masland points out the relationship between hemispheric domi- nance and tendencies toward reversal in visual perception input and the role they may play in reading ability. The very important relationship between research on problems of visual information processing and reading and the health and educational services available to the general public is outlined by Richardson. Per- haps changes in this interservice area of societal organization can con- tribute more to improving reading achievement than can changes in other areas of the problem. The conference concludes with a panel discussion among reading specialists. The panelists attempt to relate various pre- sentations to the development and treatment of reading disabilities; they give their opinions of the worth of interdisciplinary and interlevel com- munication as a means of applying research findings to human problems. 13

Next: Learning and Not Learning to Read: Current Issues and Trends »
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