Developmental trends in visual scanning.

DEVELOPMENTAL TRENDS IN VISUAL SCANNING

Mary Carol Day1 HARVARD UNIVERSITY

I. 11.

INTRODUCTION .........................................

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DEMONSTRATION OF A SYSTEMATIC STRATEGY FOR THE ACQUISITION OF VISUAL INFORMATION . . . . . . . . . . . . . . . . . . .

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111. MAINTENANCE OF A STRATEGY ACROSS VARIATIONS IN THE CONTENT AND ARRANGEMENT OF STIMULI . . . . . . . . . . . . . . . A. THE EFFECT OF STIMULUS STRUCTURE AND STIMULUS ATTRIBUTES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. CONTEXT SUPPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. CONTEXT INTERFERENCE . . . . . . . . . . . . . . . . . . . . . , . . . . . . . .

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IV . FOCUS ON ASPECTS OF THE VISUAL STIMULI MOST INFORMATIVE FOR THE SPECIFIC TASK . . . . . . . . . . . . . . . . . . . . . . A. FOCUS ON THE INFORMATIVE PORTIONS OF A DISPLAY . B. THE VIEWER'S QUESTIONS DURING VISUAL SCANNING..

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V.

EXHAUSTIVENESS AND EFFICIENCY OF VISUAL SCANNING . A. COMPARISON AND MATCHING-TO-STANDARD TASKS. . . . B. OUTLINED SHAPES AND REALISTIC VISUAL SCENES . . . . .

VI . SPEED OF VISUAL SCANNING VII . FIELD OF VIEW

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VIII. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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'Present address: The Learning Research and Development Center, University of Pittsburgh, Pittsburgh, Pennsylvania. 153

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I. Introduction In the visual environment a tremendous amount of varied information is potentially available to the perceiver. Although our field of vision spans about 210”, sharp and detailed vision is possible only within the small foveal region of the retina, which covers approximately 2”. Thus detailed perception requires movement of the eyes and successive fixations about the visual field. Visual scanning is the process by which the individual actively, selectively, and sequentially acquires information from the visual environment. While the term visual scanning most frequently refers to the sequential allocation of attention by successive eye movements, attention can also be selectively directed within a fixation (e.g., see Engel, 1971; Sperling, 1960). In this paper overt visual scanning will receive primary emphasis, although the direction of attention to certain areas within a fixation will be discussed where relevant. Visual scanning can be viewed as a “perceptual-motor” process, but it can also be viewed as a cognitively-mediatedprocess which reflects the individual’s interests, his expectations about the visual environment, and his strategies for acquiring visual information. Thus visual scanning patterns (the duration, location, and sequence of fixations), considered as overt behavioral correlates of some ir ternal mental processes, offer another window through which to view the changes which occur with development. The purpose of this paper is to provide a review of the developmental literature on visual scanning, identifying some general changes in scanning which occur during the preschool and elementary years. Data from numerous studies have demonstrated age differences in performance on tasks which require scanning. Eye movement data, both independently and in conjunction with other dependent variables, provide the most precise information on visual scanning. However, data on developmental changes in eye movement patterns are still quite limited, perhaps because of the difficult and restricting nature of eye movement recording and the time-consuming analyses required of these records. Therefore studies in which a variety of dependent variables and experimental tasks was used contributed to the attempt to identify developmental trends. One additional point should be made before proceeding further. Age, like socioeconomic status or sex, is a “package” variable. Pointing out that a particular behavior changes with age serves only as a description, and does not indicate the cause of the change nor specify the mechanism of the change. Wohlwill (1970) has argued that although cross-sectional research contrasting the performance of different age groups tends to make age an independent variable, the interest of the developmentalist is not in age per se, but is in the behavior changes that occur over an age span. The data from many of the studies reviewed here only described age differences in behavior within the experimental context. The relationship between characteristics of the age changes and independent

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variables has not been extensively probed, nor has attention been focused on explaining the age differences. In this paper the phrase “age differences” will be used with reference to the performance differences found at various ages in the primarily cross-sectional studies. This phrase is not meant to imply that the behavior is a function of age in a causative sense. In a number of studies, the greater familiarity of older children and adults with the stimulus materials and the task requirements may constitute a particularly important factor in the changes found over age. Furthermore, the research is too spotty to allow plotting trends precisely across ages or locating specific transition points, if they do exist. Six developmental trends can be identified in the literature on visual scanning. The trends will be stated in general terms here, and their scope and exceptions will be discussed. Comparing data from a variety of experimental contexts serves to highlight the importance of the relationships among the child’s knowledge and strategies, the specific stimulus materials, and the difficulty of the experimental tasks. In general, with age there is: 1‘. Increased demonstration of a systematic plan or strategy for the acquisition of visual information. 2. Increased maintenance of a strategy across variations in the context and arrangement of stimuli. 3. More focus on aspects of the visual stimuli most informative for the specific task. 4. Increased exhaustiveness and efficiency of visual scanning. 5 . Increased speed of visual scanning. 6. And, perhaps, an enlarged field of view. Each of the trends will be discussed in turn, commencing with a definition of the trend and a review of the evidence supporting that trend. A discussion of the main issues raised by the data and some possible interpretations will follow.

11. Demonstration of a Systematic Strategy for the Acquisition of Visual Information Since only limited information is obtained in each visual fixation, numerous fixations are typically required to scan a visual array. Many researchers have reported age differences in the extent to which the child’s sequential exploration is “systematic” or “nonsystematic.” These terms are generally defined operationally within the context of particular experiments, but a broader interpretation of them leads to several useful distinctions. “Nonsystematic” exploration by the child typically means that adults who are observing his successive encounters with the visual field do not see a task-appropriate pattern in the responses. However, a “nonsystematic” series of responses

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may nevertheless be rule-governed. The child may be following rules, but rules which the adult considers inadequate for the task. For example, in order to determine if two houses with six windows each are identical, adults will compare the windows in the corresponding locations on the two houses. A young child, when asked if the houses are the same, might search for a symmetrical window in each of the houses. This child would be following a rule, but it would not succeed by adult criteria. In general, a sequence of responses is termed “systematic” (or organized or patterned) if consistent, task-appropriaterelationship can be seen among the separate responses of the sequence. In comparison to a nonsystematic strategy, a systematic strategy is more likely to be exhaustive (i.e., to cover all of the visual array) although it could be applied to only a portion of an array. Enough responses must be made, however, for a pattern to be identified. Also, systematic responses are typically nonredundant, usually being spatially adjacent or alternating between each item in one display and the spatially corresponding item in another. A further differentiation can be made within the category of “systematic performance.” A child may either use a perceptually-given pattern or impose a pattern of his own on the array. A perceptual array may itself be sufficiently patterned that the child only needs to choose a starting point and a direction, and then use a relatively simple systematic strategy of following the clear contour of the array. If the child’s performance is systematic on patterned arrays (e.g., on linear arrays or arrays which form a circle or triangle), we cannot conclude that the child is imposing the pattern on the array. Rather, he may be simply following the pattern provided by the array. When, however, the child exhibits systematic performance on an array with no simple contours (i.e., when the child scans from left to right starting at the top and proceeding through each successive row of a 5 X 5 matrix array), the child must then make a series of decisions at choice points. Here we can assume that the child is imposing the pattern on the array. Two types of tasks have shown an increase with age in children’s use of a systematic scanning strategy. One type simply requires the subject to name all of the pictures in an array. The other one requires the subject to compare two displays or forms in order to make a “same” or “different” judgment. In the first case the systematicity of visual scanning is inferred from the pattern of naming. However, research is needed where eye movements are recorded simultaneously with naming responses in order to verify the correspondence of scanning and naming patterns, for the two might be different. All of the studies in which children have been asked to name the items in arrays of different configurations have clearly revealed an increase in systematic scanning and a decrease in errors of omission and commission between approximately 3 and 11 years of age (Dorman, 1971; Elkind & Weiss, 1967; Gottschalk, Bryden, & Rabinovitch, 1964; Hansley & Busse, 1969; Kugelmass

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& Lieblich, 1970; Matheny, 1972; Teegarden, 1933). In most of these tasks systematic scanning patterns consisted of adjacent responses which mirrored contours or formed consistent horizontal and/or vertical patterns. In addition to an overall increase in systematic scanning with age, an interaction between age and stimulus configuration was found in the naming studies. Young children exhibited a more systematic pattern of exploration on simply patterned arrays than they did on matrix arrays or random arrays (i.e., arrays with pictures positioned to suggest no pattern). [In most of these studies the number of pictures was not held constant across stimulus arrangements; the random and matrix arrangements included more pictures than the arrangements which formed simple outlined figures. Dorman’s (1971) study was the notable exception, and her results were similar to those of the confounded studies.] Elkind and Weiss (1967) found that all of their 5-year-olds were systematic in naming the pictures in a triangular array whereas only half were systematic in exploring a random array. Other studies have shown that children are more systematic when pictures are arranged in the form of a T, a circle, vertically, or in a square than when they are arranged either randomly or in a matrix (Dorman, 1971; Kugelmass & Lieblich, 1970; Matheny, 1972). In addition, Dorman (1971) showed that providing structure by giving explicit instructions, as well as by presenting a simply patterned array, increased the organization of young children’s responses. In Dorman’s study, 3-year-olds performed least systematically when the stimuli were arranged randomly and when instructions were least explicit (i.e., “pick up some marbles” rather than “find a raisin hidden under one marble” or “pick up each marble once”). It thus appears that systematic exploration is a joint function of age and stimulus configuration. The child can respond systematicallyon a naming task by using a perceptually-given pattern at a younger age than he can impose a pattern which is not perceptually given. As discussed previously, systematic performance on the patterned array requires fewer decisions and a less complex strategy. More precise assessments of visual scanning made by photographing the eye movements of children during comparison tasks have also indicated an increase in systematic scanning with age (Nodine & Evans, 1969; Nodine & Lang, 1971; Nodine & Steuerle, 1973). For example, Nodine and Lang (1971) asked children to compare four-letter pseudowords in order to make a “same” or “different” judgment. In this task the appropriate systematic strategy is to make paired comparisons, i.e., to compare the letters in the same relative positions of the two words. Third graders made more paired comparisons than kindergarten children. Indeed, the kindergarten children tended to scan sequentially the letters within words more frequently than those between words. Differences were also found in the manner in which kindergarten, first grade, and third grade children compared graphemes which were enlarged to require fixations on different letter features

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(Nodine & Steuerle, 1973). The fixation patterns of the first and third graders were simpler and less redundant than those of kindergarten children. In a study conducted by Vurpillot (1968), similar age differences were found in the comparison of component parts of a visual stimulus. Vurpillot recorded the eye movements of children (3.9 to 8.8 years) as they compared pairs of houses, each house having six windows, in order to make a judgment of “same” or “different.” The youngest group of children appeared to scan the windows of the houses nonsystematically, making few paired comparisons between the corresponding windows of the two houses. The number of children making paired comparisons increased with age, and by 8.8 years 18 of 20 subjects made paired comparisons. All of these studies indicated an increase in task-appropriate, systematic scanning with age. The young child, especially the child younger than 5 years of age, is less likely than the older child to partition a display into a series of systematic encounters unless the display itself provides a concrete guide in the form of a simple perceptual pattern. When the child does not exhibit a systematic pattern of exploration, however, the reasons are not apparent. Perhaps the child does not understand what is expected of him; he may not understand the requirements of the task. Alternatively, the child may simply not produce a strategy that specifies more than a starting point and an initial direction; formulating a more extensive strategy may not occur to the child or he may be unable to formulate a more extensive strategy. Finally, the child may formulate a strategy but may be unable to use it for extended exploration, perhaps because he forgets the strategy or because he is distracted from his strategy by the stimulus content. These alternative explanations have not been researched extensively in visual scanning, although in other contexts they have been labeled comprehension, production, and mediation “deficiencies,” respectively (Bem, 1970; Flavell, 1970; Flavell, Beach, & Chinsky, 1966; Moely, Olson, Halwes, & Flavell, 1969). Data relevant to someofthesepossible explanationswill be discussedin SectionsIIIandIV.

111. Maintenance of a Strategy across Variations in the Content and Arrangement of Stimuli Young children’s performance on a visual scanning task is affected by characteristics of the visual stimuli to a greater extent than is the performance of older children and adults. The performances (or dependent variables) which have been assessed as a function of stimulus variation include the pattern of exploration, the accuracy of recognition or matching, and response latency. Three main types of variation in stimuli have been studied: the configuration or arrangement of a number of stimuli; the presence of visual noise (ix., visual information un-


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necessary for the task); and the structure or attributes of the individual stimulus (e.g., symmetry or complexity). These variations may either support or interfere with performance, depending upon the task requirements and, probably, the subject’s strategy. Stimulus variations which serve to improve performance on the dependent measure being used are said to offer context support, while those which disrupt performance are said to provide context interference. On the types of visual stimuli and tasks used in most visual scanning studies, young children appear to be more susceptible to both context support and context interference than older children and adults. With increasing age the child generally shows an increasing independence of the particularities of the visual field, which results in a greater consistency of performance across stimulus variation (cf. Gollin, 1968; Wohlwill, 1962).

A. THEEFFECTOF STIMULUS STRUCTURE AND STIMULUS ATTRIBUTES Younger children appear to be more affected than older children by the particular attributes of the stimuli used in the experimental task. The symmetry of shapes, the “complexity” of shapes (generally defined by number of angles), and the location of the focal point of a figure are all stimulus variations which have been used in the studies which demonstrate this trend. The results of two studies using matching-to-standard tasks indicated that the search time of children varied more as a function of stimulus characteristics than did the search time of adults. Forsman (1967) found that both asymmetry and complexity of form slowed the search time of third graders more than that of sixth graders and adults. H. A. Spitz (1969) found that fourth graders’ search time was slowed more than seventh graders’ by lowering the “information value” of the standard to be located, where information value was defined either by number of angles or by independent raters’ judgments. A substantial amount of research has been focused on how the location of a focal point affects the recognition of tachistoscopically presented forms. For simple stimuli a focal point is defined as “the one differentiating feature in an otherwise homogeneous figure or card,” such as an acute angle or a convex portion. “By extension, the focal feature for complex figures can be defined functionally-behaviorally-as whatever kind of feature the young child prefers at the top [Braine, 1972, p. 1831.” Ghent (1961) found that young children best recognized a briefly-presented form when the focal feature was at the top. She hypothesized that children younger than 5 years of age begin scanning a form at its focal point and proceed in a downward direction, whereas older children start at the top of a form regardless of the location of its focal point. A substantial body of research has been generated in support of this hypothesis (Antonovsky & Ghent, 1964; Braine, 1965, 1968, 1972; Ghent, 1961; Ghent & Bernstein, 1961;

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Harris & Schaller, 1971; Strang, 1967). Thus processing proceeds in a downward vertical direction (on forms with a vertical main axis) at all of the ages studied, but the starting position, or the “phenomenal top,” changes at around 4 or 5 years of age. One characteristic of the stimuluDits focal point-determines the starting position of the scan for children under 5 , whereas children over 5 years of age appear consistently to impose a starting point at the top of the stimulus.

B . CONTEXTSUPPORT Context support for systematic scanning has been reported on naming tasks, on a comparison task, and on a matching-to-standard task. All of these studies suggest that young children can scan systematically with context support before they can without it. In the naming tasks previously described, the interaction between age and stimulus configuration offered evidence for the importance of context support for young children (Dorman, 1971; Kugelmass & Lieblich, 1970; Matheny, 1972). Children systematically named pictures arranged linearly or as a simple outlined form at a younger age than they systematically named pictures in a matrix or random array. The value of context support for systematic comparison was demonstrated in a study by Day and Bissell (in preparation). The Vurpillot (1968) comparison task, requiring paired comparisons of windows in the corresponding locations of two houses, was administered to 4-year-olds who were asked to justify their judgments verbally or by pointing to the windows of the houses. The justifications used by the children were categorized. Twenty-five percent of the 32 children used a paired comparison strategy on houses which were the pame but nor on houses which were different. When the houses were identical, the children used the identical windows to aid their comparisons. Given some notion that windows in the same relative location of each house should be compared, and given some perceptual help in the form of identical windows in the corresponding locations, children performed as would adults. On pairs of houses which were different from one another, however, children could not maintain the paired comparisons without the perceptual support provided by the identical windows, and they resorted to other inappropriate strategies. A similar finding was reported by Venger (1971), who asked children to find a match for a black strip of a specified length among 20 other strips of varying length. He found that 3- to 5-year-olds conducted a systematic search of a linearly-arranged array only when they depressed keys beneath the strips, thereby making a record of past guesses. Their search became disorganized, however, if the keys indicating their guesses did not remain depressed. Children of 5.5 to 7 years of age, in contrast, were able to maintain a systematic search without a concrete record of their past guesses.


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These studies suggest that an increase in systematic performance occurs at certain ages as a partial function of the availability of supportive perceptual information. Although longitudinal research is needed, these studies suggest the following developmental sequence in visual scanning: First, subjects are not able to explore an array systematically, regardless of characteristics of the array; second, subjects can conduct a systematic exploration by following a given perceptual pattern; and finally, subjects can impose a pattern that is not directly given by the perceptual array.

C. CONTEXTINTERFERENCE In some cases particular stimulus arrangements or visual noise result in the disruption of performance, or context interference. While the value of context support for the systematicity of visual scanning was discussed above, the disruptive influence of stimulus characteristics is revealed by other dependent measures-the accuracy of form recognition and response latency. One type of context interference may be created by the arrangement of stimuli. The positive effect of a patterned array was previously discussed, but on some tasks a clearly patterned array may not improve performance, as was found by Rand and Wapner (1969). Rand and Wapner presented 8- to 18-year-oldswith a “segment identification test” which required the subjects to match a simple isolated figure with 1 of 16 figures in an array. In one condition the figures of the array formed a contour; in the other condition the figures of the array were arranged randomly. Although the time required for a match decreased wiEh age, the primary finding was a significant interaction between age and configuration. The younger children had significantly longer search times on the patterned array than on the random array, while the configuration of the array had little effect on the search times of adults. Thus the arrangement of stimulus elements in a pattern positively influenced performance (by increasing its systematicity) on naming tasks but negatively influenced performance (by lengthening search time) on the segment identification task. Although the dependent variables were different, the studies do suggest, at a gross level, opposite effects of a patterned array. The studies differed, however, in the “tightness” of the contour formed by the distinct elements. In the naming tasks the pictures comprising the contour were quite clearly distinct from each other, but in the Rand and Wapner task the figures were pushed together to form a contour and were Jess distinct as independent units. Thus the parts had to be separated from the whole in order to identify the matching figure. Although Rand and Wapner did not describe the adults’ strategies, they may well have used the contour as a guide for the direction of the scan while also segmenting the contour to view the individual elements, thereby dealing with the parts and the whole simultaneously. Several studies have dem-

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onstrated that children have trouble dealing simultaneously with the parts and the whole of a visual form (Elkind, Koegler, & Go, 1964; Meili, 1931). Thus context interference may have been produced by adding to the task a requirement which is especially difficult for young children. Another type of context interference can occur when visual noise (irrelevant visual information) is added to a stimulus display. There is limited evidence that with increasing age the performance of children is less influenced by the presence of irrelevant information. Munsinger and Gummerman (1967) varied the type (random or systematic) and amount (low or high density) of background noise against which second grade, fifth grade, and college students tried to identify forms presented tachistoscopically. They found that children were much more adversely affected by the noise than were the adults. In a similar study, but one requiring tactual form discrimination, Gollin (1960, 1961) found that tactual noise (irrelevant tacks scattered around a shape formed by larger tacks) was more disruptive for the recognition performance of younger children than for older children and adults. The significance of the subject’s strategy in determining the effect of visual noise was demonstrated in a study reported by Hochberg (1970). Hochberg, Levin, and Frail presented two versions of short stories to first and second graders. In the unfilled version normal spaces were left between words, but in the filled version meaningless symbols were placed between words. When the 8 slowest and 8 fastest readers (of 24) on the unfilled version were compared with respect to their reading speed on the filled version, it was found that the faster readers, but not the slower readers, decreased in reading speed. The slower readers, who were still scanning letter by letter, would normally make little use of the blank spaces between words for directing their next eye movements. The faster readers, who do not scan letter by letter, might normally use these peripheral cues to guide subsequent fixations. When the cues are no longer available, their performance suffers. On a form recognition task it also seems likely that the subject’s strategy in interaction with the stimulus display would determine the effect of noise. If the child attends to relevant and irrelevant stimuli indiscriminately, we might expect noise to be more disruptive than if the child were to selectively attend to relevant stimuli while ignoring irrelevant stimuli. There is substantial common belief that with age children attend more selectively. However, surprisingly little concrete evidence exists for age changes in visual selective attention although there is evidence for age changes in auditory selective attention (e.g., see Doyle, 1973; Maccoby, 1969). In addition to the studies just described, incidental learning tasks provide some indirect evidence about selective attention to visual stimuli. In incidental learning tasks children are exposed to stimuli which are not referred to in the task instructions but which are included in subsequent tests of retention. These tasks have typically indicated that the retention of task-irrele-


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vant information remains constant across age or increases between the ages of approximately 7 and 1 1 years and then decreases between 11 and 13 years. Simultaneously, intentional learning increases consistently between 7 and 13 years (Druker & Hagen, 1969; Hagen, 1967; Maccoby & Hagen, 1965; Siege1& Stevenson, 1966; Steveson, 1972). The increase with age in the ratio of central to incidental learning has been interpreted as indicating developmental changes in selective attention to stimulus features critical for the task. The absence of a consistently positive relationship between central and incidental learning in younger Ss and of a consistently negative relationship between them in older Ss suggests that such incidental learning tasks are not maximully sensitive to the assessment of age changes in selective attention. Furthermore, the relationship between age and selective attention is undoubtedly more complex than this paradigm indicates. For example, age differences in incidental learning are somewhat dependent upon properties of the stimulus. If incidental and central components are integrated in a colored shape, for instance, incidental learning increases with age (Druker & Hagen, 1969; Hale & Piper, 1973). Furthermore, one study has indicated that in a task where no one stimulus attribute is designated as relevant, 8-year-olds attended more to a redundant stimulus attribute than did Cyear-olds (Hale & Morgan, 1973). In general, these studies suggest that children become more flexible in their allocation of attention with age and become more capable of differentiating between situations in which selective attention to a limited amount of the available information will and will not be useful. In sum, with age children are better able to maintain a strategy over variations in stimulus arrangement and stimulus attributes. The child’s performance reveals “a decreasing dependence of behavior on information in the immediate stimulus field [Wohlwill, 1962, p. 731.” This does not necessarily mean that the child comes to use perceptual information less, however. Rather such information comes to have less of a determining influence on his behavior as the child begins to use it more selectively. While the first developmental trend focuses simply on the increase with age in children’s demonstration of a systematic scanning strategy, this second developmental trend points to the decreasing influence of stimulus materials on the child’s demonstration of a systematic strategy.

IV. Focus on Aspects of the Visual Stimuli Most Informative for the Specific Task With age and with familiarity children reveal an increasing tendency to focus on the portions of visual stimuli which are most informative for the task at hand. Familiarity is considered jointly with age here because it appears to exert a

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critical independent inkence on the demonstration of this &end, and in many experiments age and familiarity are confomckd. The “informative” portions of stimdi 8ce those which provide information necessary for the assigned task. Thus the informative portions are not fixed an8 constant properties of stimuli. Different segments of a scene or figure are informative in responee to different questions. Yarbus (1967) has demonstrated convincingly tkat tke portions of a pichue fixated by adults are a function of the questions they have been asked about the pictwt, i.e., by “the problem facing the observer at the moment of perception [p. 1961.’’ The perceiver is engaged in a p p s i v e search for information; he is seeking answers for questions cw testing hylpotheses when he samples the v i s d world (Green & Courtis, 1966; k h b e r g , 1%8, 1970,1972). Since children do not focus as exclusively as adults on PoptiORs of a display which. are most iREormative for the specific task, children and dd?s may be asking different questions or testing diffcmtt hypotheses-a p d d l c y that will be explored later in this section.

A. FOCUS ON THE INFORMATIVE PoRT’fONS OF A &PLAY Within Eleanor Gibson’s (1969) theory of perceptual learning, this one trend is considered to be the essence of all perceptud learning: “The criterion of perce-1 karning is thus an increase in specificity. What is hmed can be described as detection of properties, patterns, and distinctive featmes [p. 771.” Gibson’s research supporting the notion of increasing diffeteatiatioR among stisnuli with experience has primarily used outlined forms or line &signs, suck as Roman capital letters or “scribbles,” which differ in number of distinctive features of in specific transformations. For exawnpie, in m e&y study Gibson and Gibson (1955) asked subjects of three ages (6-8 years, 8-5-11 years, and adults) to identify a standard, four-coil scribble when it ap)eYed in a pack of carcts containing replicas of the standed a d mnerous variants. OR the first trial the younger children made more incorrect identity judgments thrrn did the oider children or adults. With uncorrected practice all subjects improved in performance, but the younger children improved less than the d d r r subjects. Furt h e m r e , the number of errors increased as the number of stimulus features by which an item difired from the stanchi decreased. In a comparable study, Gibson, Gibson, Pick, and Osser (1962) asked 4- to 8-year-olds to match standard letterlike forms with identical figures displayed among 12 transformations of the standard figure. The total number of confusion errors decreased with age, although the specific transformations varied in difficulty. The increasingly more accurate discrimination among these figures and among letters of the alphabet occurs, according to Gibson, because distinctive features-those features which discriminate among figures-are learned through experience. More precise data on age changes in fmus on informative portions of stimuli come from a series of studies by Nodine and his collaborators (Nodine & Evans,


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1969; Nodine & Lang, 1971; Nodine & Steuerle, 1973), who recorded the eye movements of children comparing pairs of words or graphemes. The data from these studies indicate that with age and with experience with letters and words, children focus more often on their distinctive features. For example, in the study by Nodine and Steuerle (1973) mentioned above, kindergarten, first grade, and third grade children compared letters which were enlarged to necessitate overt eye movements. They found an increase in focus on distinctive features (as defined by Gibson) with age, although only 29% of all fixations fell on distinctive features. Perhaps some of the most provocative research on the eye movements of children during visual scanning was conducted by the Soviet psychologists Zinchenko (Zinchenko, 1965; Zinchenko, Chzhi-tsin, & Tarakonov, 1963) and Pushkina (1971). Both reported differences in the locations of fixations as a function of age (especially during the initial inspection of a figure) and as a function of familiarity with the particular figures and/or the task. Zinchenko el al. (1963) photographed the eye movements of children while they were initially viewing an irregular shape in order to identify it later. The eye movements of a second group of children were photographed during the recognition phase. From 3 to 6 years of age the number of eye movements made during the initial inspection phase increased, and the location of the fixations changed as well. While the 3-year-olds fixated primarily on the camera lens at the center of the figure, the 6-year-olds fixated almost exclusively along the contours of the figure. The older children thus obtained information about shape which was important for later recognition. Interestingly, during the recognition phase the eye movements of the second group of 3-year-olds were similar to the eye movements made by the 6-year-olds during the initial inspection phase. Even though the use of different groups of children for eye movement recording during the inspection and recognition phases weakens the methodology of the study, the data suggest that with familiarity the younger child begins to scan in a manner comparable to the older Ghild. From these results Zinchenko et al. (1963) concluded that “the development of perceptual acts follows the line of identifying specific sensory content, increasingly adequate to the material presented and to the task facing the subject [p. 61 .” The problem for the young child is that he does not know which stimulus attributes are relevant for the task. Zinchenko’s group postulated two stages of perceptual activity. During the first stage of perception the subject must determine what content is significant. If the material is familiar or if the subject is informed of the significant content, then this phase may not be apparent. During the second phase the subject focuses solely on the information relevant to the task. Pushkina’s (1971) data and analyses are quite congruent with those of Zinchenko. In a study of the transposition of size relations, Pushkina found that subjects made more eye movements while comparing stimuli during their first

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trials than during their later trials. Over trials their eye movements became simpler and linear, appropriate and efficient for the required task of discerning the size of the forms. Pushkina also reported that older children were more likely than younger children to show the decrease in eye movements as they mastered the &imposition of relations. The onenting-investigatory activity of a child passed through three stages in its development with transposition of relations: The first stage (children up to and including the age of 3) was characterized by expanded orienting activity during transposition, with a relatively small number of correct answers. For the second stage (4- and 5-year-olds), orientation was more restricted, but it expanded when new shapes were presented in control trials. The third stage (6-year-olds) was distinguished by a restricted orientation with error-free estimation of size relations (Pushkina, 1971, p. 231).

Pushkina’s results thus suggest that children under 6 are less likely to make eye movements which gather only the information needed for the task than are children 6 years of age and older. These data are consistent with the previously noted changes over age in selective attention to only task-relevant information. Zinchenko’s group would expect adults, in their first encounter with unfamiliar visual material such as aerial photographs or topographical maps, to go through the phases most typically seen in children. What Zinchenko and his co-workers did not point out, though, is that children and adults may well use different strategies when they first encounter unfamiliar or unrecognizable perceptual displays. Although the irregular figures were unfamiliar to the older children, they may have had a different notion of how to scan and of what content might be relevant. Indeed, the results of a study by Mackworth and Bruner (1970) indicate that the fixations of children and adults differed most on blurred photographs of unknown content. Mackworth and Bruner recorded the eye movements of 6-year-old children and adults while they were viewing colored photographs. One group of subjects viewed a sharp photograph, followed by viewings of the same photograph in a blurred condition and then in a very blurred condition (the “inspection series”). Another group of subjects viewed the photographs in the opposite order and attempted to identify the object in the photograph (the “recognition series”). Based on adult ratings of “informativeness” (i.e., ratings of the extent to which the segment could be recognized on a second occasion), an “informative index” was calculated for each subject’s fixations. On the sharp pictures in the inspection series the fixations of the children were as informative as those of adults, whereas in the recognition series adults made more informative fixations on the blurred photographs. These data point to an increasing focus with age and familiarity on stimulus features informative for a specific task. Several underlying factors are probably important for these age-related changes in attention to task-relevant information,


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including: comprehension of the task requirements and of what constitutes appropriate performance in a task; knowledge of the visual world (expectancies about regularities of the visual environment and knowledge of culturally-used differentiating features of stimuli); strategies for internally encoding (representing) that knowledge; the cognitive capability required for handling the conceptual distinctions necessary for the task; and the ability to attend selectively to informative aspects of stimuli when those aspects are known. If visual scanning is considered to be a purposive search for information to answer questions or to confirm hypotheses, then the first four factors would be expected to influence the types of questions asked by the subject and thereby influence his visual scanning. The fifth factor (which was discussed briefly in Section 111) would influence the extent to which he can ignore information which is irrelevant to his questions.

A. THE VIEWER’S QUESTIONS DURING VISUAL SCANNING Consider the Vurpillot (1968) task, where the subject was asked if pictures of two houses were the same. Although the question most adults would attempt to answer is “Are all pairs of windows in corresponding locations on the two houses identical?,” 4-year-olds may ask “Are any of the windows on the two houses the same?” or “Have I seen any windows like these on previous pairs of houses?” Although Vurpillot (1968) inferred the questions asked by subjects from records of their eye movements and subsequent judgments, Day and Bissell (in preparation) questioned children after each comparison to determine the reasons for their judgments. They found that the subject’s search was, in most cases, directed by his conception of the task and by the questions he was asking-uestions such as those suggested above. A necessary prerequisite for an adultlike search is posing the question as an adult would; herein may lie many of the differences in adult and child scanning patterns. In a similar vein, Daehler (1970) has proposed that before subjects can make “investigatory responses” to ascertain the “real” characteristics of illusory or ambiguous stimuli, they must conceptually differentiate the real from the phenomenal. Eye movement records of children participating in a conservation task also indicated that eye movements reflect the children’s conceptions of the task requirements and their questions about the stimuli (Boersma, O’Bryan, & Ryan, 1970; O’Bryan & Boersma, 1971). Perceptual activity was least in nonconservers, somewhat variable in transitionals, and greatest in conservers. The conservers demonstrated more couplings (shifts of fixation from one element to another) and covered more of the informative aspects (e.g., length and width of a container) of the stimulus elements than nonconservers. Also, while the nonconservers fixated significantly more on the element chosen as “greater than,” the conservers fixated approximately equally on transformed and nontransformed elements.

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None of these studies, however, attempted to manipulate the questions asked by the child in the experimental situation to determine whether the change in questions would be reflected in eye movements. In a more recent study, Boersma and Wilton (1974) reported that nonconservers with conservation training demonstrated more visual activity and less centration than nonconservers without training. In addition, the eye movement patterns of the trained conservers were quite comparable to those of the untrained conservers in the previous studies. This study suggests that direct comparison of the scanning patterns of the trained conservers before and after training would have revealed changes as a function of the child’s cognitive approach to the task. Olson (1970), also, has argued that eye movement patterns vary as a function of the viewer’s questions and assumptions. In one study Olson asked children to determine whether each of four variants differed from a “standard” house. On the initial trials Olson found that 6- and 7-year-olds made correct judgments much more frequently than did 4- and 5-year-olds. Eye movement records indicated that the older children focused more frequently than the younger children on all four of the significant features (e.g., door, chimney), possibly because they knew what features were likely to be important whereas the older children did not. Results consistent with this interpretation were found when children were presented with a diagonal comprised of checkers and then were asked to recognize it among several alternatives. The older children were again more accurate than the younger children were. But when the children viewed the alternatives and then looked again at the diagonal, both younger and older children were 100% correct. Using these and other data, Olson posited that visual search is a function of the child’s assumptions of what to look for in the specific task, i.e., of the child’s notions of the alternatives among which he must choose. The findings of Olson, Zinchenko et al., and Gibson all indicate‘that young children increase the appropriateness of their scanning and the accuracy of their discrimination with practice and with exposure to the stimuli among which they must discriminate. These results suggest that younger and older children have different conceptions about what features are important for the task; they initially ask different questions. Older and younger children may also differ in their typical manner of encoding visual stimuli, i.e., in the manner they store or remember stimuli. Performance on matching tasks suggests that young children may attempt to encode stimuli wholistically, without analyzing and then resynthesizing their components. Rand and Wapner ( 1969) investigated developmental differences in encoding by comparing the speed of 9- to 17-year-olds on an embedded figures task with either simultaneous or successive presentation of the simple figure and the complex figure in which it was embedded. Differences in speed within age groups for these two modes of presentation were smaller for the 9- and 10-year-olds than for


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the 12-, 13-, 15-, and 17-year-olds. If the younger children first formed a general impression of the simple figure, its lack of availability for detailed comparisons would have little effect on performance, as was found. However, if subjects successively compared certain distinctive features across all of the components, the absence of the simple figure throughout the search would affect performance more adversely, which it did for the older subjects. Similarly, on a Matching Familiar Figures test, Drake (1970) found that adults made more comparisons of specific features across the different figures than children did. It must be noted, though, that differences in manner of comparison across figures have been found within as well as behveen age groups, with such cognitive style characteristics as reflectivity-impulsivity influencing performance (Drake, 1970; Siegelman, 1969; Zelniker, Jeffrey, Ault, & Parsons, 1972). A distinction can be made on these types of tasks between two primary types of encoding: naturalistic-encoding a figure by its similarity to the form or to a specific feature of a familiar object or figure, e.g., noting that an unfamiliar figure looks something like a dog; and conceptual-analytic-encoding a figure as the intersection of several classes or of several values within one class, e.g., noting that a figure is red and is comprised of both straight and curved lines (Rand & Wapner, 1969). The first type appears to be favored by young children, whereas adults can probably use each type as it is appropriate. The Soviet psychologist Venger ( 197 1) has offered a parallel interpretation of scanning changes during the preschool years. He posits a move from the use of “objectoriented templates” to the use of “standard or criteria] models.” Object-oriented templates “globally reflect the objective properties of objects [p. 561 while standard or criteria] models “can represent the separate properties of objects in their objective and mutual interconnections and relations [p. 541 .” Developmental changes in the manner of encoding visual characteristics are closely tied to general cognitive development. For example, a conceptual analysis on the basis of several dimensions requires the ability to abstract and remember the specific dimensional characteristics. The general literature on cognitive development (Case, 1972; Pascual-Leone, 1970) and the more specific literature on multiple classification (Inhelder & Piaget, 1964; Kofsky, 1966; Parker & Day, 1971) suggest that before 5 to 7 years of age the child has difficulty considering two or more attributes simultaneously. Similarly, a detailed analysis of a form requires a consideration of the components of the form and its gestalt simultaneously. These abilities, typically considered to be cognitive, are clearly reflected in the child’s visual scanning. In summary, with age the child reveals an increasing focus on portions of visual stimuli which are most informative for the specific task. Visual scanning can be viewed as a purposive search for information, and the information the subject seeks is influenced by a number of factors. Among them are comprehension of the task requirements, knowledge of the visual world, manner of

.”

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encoding that knowledge, and the cognitive ability necessary for handling the demands imposed by the task.

V . Exhaustiveness and Efficiency of Visual Scanning The fourth developmental trend concerns the scope of visual scanning. With age it appears that there is an increase in both the exhaustiveness and efficiency of visual scanning. “Exhaustiveness” increases as the proportion of the total visual scene covered increases. “Efficiency” is essentially an exhaustiveness which is limited to relevant aspects of the visual stimulus. Optimal performance on some tasks does not require exhaustive scanning. For example, on comparison tasks requiring “same” or “different” judgments, it is appropriate to scan only until a difference is found. When only task-relevant aspects of the visual field are scanned and task-irrelevant aspects are ignored, the visual scan is termed efficient. If a visual scene is only partially covered and some task-relevant aspects are omitted, the scan is termed partial rather than efficient. On comparison or matching-to-standard tasks where a certain number of elements or aspects of stimuli must be compared, labeling performance as partial, exhaustive, or efficient is relatively clear-cut. On some of these tasks age-related increases in exhaustiveness and efficiency appear together, as if both can be attributed to- greater comprehension of the task requirements and the ability to handle them adequately. On other such tasks, there appear to be three stepspartial scanning, exhaustive scanning, and then efficient scanning. These changes in the scope of scanning are often functionally related to the use of a more systematic scanning strategy, although the use of a strategy and the scope of its application are conceptually separable. In the inspection and recognition of outlined figures or realistic visual scenes, exhaustiveness refers simply to the proportion of the total visual scene scanned. But efficiency in these cases (and in certain matching tasks) is a somewhat looser concept referring to adequate performance with minimal visual information. Here partial and efficient scanning cannot always be distinguished simply by observing eye movement records. Labeling a nonexhaustive scan efficient or partial would require knowledgeof the adequacy or inadequacy of the subject’stask performance. Familiarity with the stimulus seems to play a major role in the exhaustiveness and efficiency of scanning figures or scenes. Much research has documented consistent relations between looking time and such variables as novelty and complexity (see Nunnally & Lemond, 1973, for a comprehensive review), but researchers have not yet adequately studied eye movement patterns as a function of age and familiarity, and their interaction. The generalizations made here must therefore be regarded as tentative. In general, it appears that similar progressions in scanning patterns are found with increasing age and with increasing familiari-


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ty. With age the initial exploration of unfamiliar scenes becomes more exhaustive. Within any one age group, exhaustiveness first increases and then decreases with familiarity. The scanning variations associated with familiarity appear to be related to the formation and use of an internal schema or image of the visual stimulus. Age differences in the inspection of unfamiliar stimuli may similarly be related to changes in the repertoire of internal representations to which unfamiliar stimuli can be assimilated.

A. COMPARISON AND MATCHING-TO-STANDARD TASKS The developmental trend toward more exhaustive scanning constitutes a major feature of Piaget’s (1969) conception of perceptual development, and much of his work on age changes in perception has used comparison and matching-tostandard tasks. Piaget distinguishes between centration and perceptual activity. Centration, the allocation of attention within a fixation, produces “field effects” which result from the “quasi-simultaneous interaction of elements perceived together in one single field of centration without the invoIvement of a displacement of fixation [Piaget, 1969, p. 31.’’ The elements centrated tend to be overestimated while the more peripheral elements are underestimated. With age the child begins to decentrate; he makes more fixations and centrations while looking at a visual display. These perceptual activities are associated with an increase in the integration of the individual centrations and their effects across spatial and temporal intervals. Piaget posited the increase of a variety of perceptual activities with age-exploration (moving from one point to another on the same element), transportation (moving from one visual object to another), spatiotemporal or temporal transposition (a collection of transportations involving relations between objects), referral (to perceptual coordinates), and schematization (formation of a generalization based on common structures or schemas of sensorimotor activities). He considered exploratory activity, in general, to be “the activity which directs eye movements and determines pauses or centrations during the examination of a figure [Piaget, 1969, p. 137.’’ On Vurpillot’s (1968) task requiring the comparison of the six windows of two houses, the eye movements of the children revealed both increasing exhaustiveness and efficiency with age. The 4- and 5-year-old children fixated about six or seven windows on each pair of houses, while children over 6 years of age tended to fixate the number necessary for an accurate judgment. On the identical houses the older children tended to be exhaustive; they fixated about 10 to 12 windows. On the different houses they tended to look until they found a pair of different windows. Because they did not continue looking after finding a difference, their performance was efficient. Three matching-to-standard tasks have indicated an increase with age in the exhaustiveness of scanning (Drake, 1970; Forsman, 1967; Venger, 197 1). The study by Venger provides an excellent example of the difference between partial

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and efficient scanning and indicates a progression from partial, to exhaustive, and then to efficient scanning with age. Venger recorded children’s eye movements while they attempted to match a standard strip of a certain Iength to one of 11 strips which were arranged in order of increasing length. The 3- to 4-year-olds typically examined only a small group of two to four elements, and the next group of elements they searched was not necessarily closer to the match. The 4to 5-year-olds typically examined eight to ten of the strips during their search and thus were exhaustive. The 5.5- to 7-year-olds, in contrast, examined fewer elements within a narrow search zone. They used their understanding of the serial order of the strips in the array to shorten their search to the group of strips most likely to contain a match to the standard. For older children the decreased exhaustiveness was highly appropriate and efficient, whereas for the 3- to 4-year-olds the focus on a small number of elements simply represented partial scanning. Finally, Pushkina (197 1) found a greater efficiency of scanning in 6-year-olds than in younger subjects. In the study described previously (see Section IV), Pushkina found that 6-year-olds gathered only information relevant t0 their judgments on a size transposition task, whereas the scanning of 3- to 5-year-olds was less restricted. In both Venger’s and Pushkina’s tasks the child’s visual scanning probably reflected the manner in which he was encoding the stimuli. Venger noted tbat in his task Ss were not able to use the serial order of the strips to shorten their s e m h until they understood the relationships of transitivity and relativity of size existing among the strips, i.e., until they could encode the relations among the elements. Similarly, efficient performance on Pushkina’s task required abstracting one specific attribute (size) and constructing relationships between objects with respect to only this attribute.

B. OUTLINED SHAPES AND REALISTICVISUAL SCENES There is limited evidence that in simple inspection tasks the exhaustiveness of

the initial scan increases with age. Mackworth and Bruner (1970) found

that the amount of picture covered (i.e., the total distance moved by an individual gaze) was less for the children than for the adults (with time held constant). Zinchenko et al. (1963) also found that with age children made more eye movements when initially inspecting an irregular shape. As described earlier, the 3-year-olds made few eye movements. The 4- and 5-year-olds made twice as many eye movements as the 3-year-olds, but their fixations were clustered at distinctive portions of the figere. By 6 years of age the eye movements were still more numerous, and they traced more of the figure’s contour. However, the familiarity of a visual stimulus seems crucial in determining the scope of visual scanning, In general, eye movements appear first to increase and then to decrease with successive presentations of a visual scene or shape. Zin-


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chenko’s group found that with relatively familiar pictures, 3- to 6-year-olds did not scan differently. The number of eye movements made by 3-year-olds was greater after familiarization; indeed, their eye movements were approximately equal in number to those made by the 6-year-olds during initial inspection. Furthermore, 3- to 6-year-olds did not differ in eye movement trajectories when viewing illustrations from children’s storybooks. Unfortunately, the authors did not mention how equivalent familiarity for all age groups with the storybook illustrations was established. As familiarity continues to increase, eye movements begin to decrease in number and viewers may again fixate only a few details of a visual stimulus. Zinchenko and his co-workers found that a group of 6-year-olds made more eye movements during initial inspection than did another group of 6-year-olds during a recognition phase after initial familiarization. Additionally, Zinchenko (1965) has found, using several other types of tasks with adults, that increasing familiarity is accompanied by a decrease in the frequency of eye movements and an increase in their stereotypy. With sufficient familiarity it appears that only a few key features are sufficient for recognition. Given the brevity of report in the translated Soviet articles, it is fortunate that other researchers have reported related data in more detail. Noton and Stark (1971a, 1971b, 1971~;cf. Spitz, 1971) presented line drawings to subjects under conditions of marginal visibility so that direct fixation on features was required. During an initial 20-second inspection period, eye movement records indicated that some Ss intermittently followed a fixed path characteristic of that particulars viewing that specific pattern. During subsequent recognition, in 65% of the cases the first few fixations and saccades were spent traversing the same “scanpath” used in initial inspection, but fewer fixations were made along the scanpath. Additional data come from Furst (1971), who was interested in the automatizing of visual attention, i.e., “a stereotyping in sampling of sensory information together with an attendant decrease in the rate of sampling of that information [p. 651.” In this study adults viewed color photographs for 5 seconds on each of 5 separate trials. Furst found clear evidence of automatizing, both within each trial and across trials. The average fixation rate decreased from more than 13 fixations per trial to 9.5 fixations per trial, and there was a decrease in the exhaustiveness of scanning on each successive trial. Furthermore, the redundancy of information sampling increased over trials. The data from another study with adults offer a parallel to the Zinchenko et al. (1963) finding that 4- and 5-year-olds fixated primarily the distinctive features of irregular figures. When adults were asked to inspect nonrepresentational polygons, Zusne and Michels (1964) found that they tended to fixate the intricate portions of complex polygons most frequently, while they scanned the outlines of simpler polygons. Perhaps with more familiarity the adults would have more

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completely scanned the contours of the complex polygons. Thus adults, as well as children, may initially exhibit a partial scan, fixating primarily the distinctive features of unfamiliar stimuli which cannot be encoded readily and completely or which cannot be assimilated easily to a similar image in the Ss’s repertoire. In summary, over the course of familiarization with visual stimuli viewers may first focus only on salient features, then scan more broadly to include more aspects of the visual stimulus, and finally rely again on a few specific features. According to numerous theoretical accounts (Hebb, 1949; Jeffrey, 1968; Venger, 1971; Zaporozhets, 1965; Zinchenko, 1965), as eye movements are made an internal model, image, or schema of the visual stimulus is being formed. As the image becomes increasingly complete, more eye movements are made. After an adequate image has been formed, however, fixations on a few significant features of the visual stimulus are sufficient for recognition. In addition to reducing the number of fixations, representations of the visual world and expectancies about visual events function to integrate numerous fixations over time by providing a framework into which the fixations can be placed. Jeffrey (1968) has offered an explanation for the increasing exhaustiveness of scanning in terms of the progressive construction of a schema, and Hochberg (1968, 1972) has offered a congruent conception of the role of the schema in the integration of numerous fixations. Jeffrey posited that the mechanism of serial habituation may account for the gradually increasing exhaustiveness of scanning. The subject orients to a particular cue, but with repeated stimulation the orienting response to that cue habituates and the subject shifts his attention to another cue. Gradually, a chain of responses is established in which the subject orients and habituates to a series of cues. Once a schema has been formed, little scanning is required for the recognition of a familiar visual stimulus (cf. Hebb, 1949). Soviet psychologists (Yendovitskaya, Zinchenko, & Ruzskaya, 1971) have explained the decreased need for exhaustive scanning with familiarity in the following manner: During the last stages in the formation of the perceptual process, for example, after the child has had a long training in recognition and differentiation of a given type of figure, the exploratory eye movements are successively shortened and decreased, fixating on the distinct, most informative characteristic of the object. At this stage a higher internalization of the perceptive process is accomplished, when on the basis of the formerly obtained, external models (for example, formed with the help of the hand or eye movements), which have been frequently contrasted with the object and corrected in relation to its properties, an internal model-a constant and orthoscopic perceptual image-is finally formed. Now, without extensive exploratory actions a quick glance at an object directed to a particularcharacteristic aspect of the object can actualize the entire “internal” model in a child and, in such a way, lead to an instantaneous judgment of the qualities of the perceived object [pp. 55-56].

Internal representations of the visual world serve another function in addition to reducing the number of fixations required to recognize familiar objects. They

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provide a framework for integrating across successive fixations, for chunking individual fixations into larger units (Miller, 1956). Hochberg (1968, 1972) has pointed out that the successive glimpses of a visual stimulus which are obtained over time and space frequently exceed the number that could be held, unconnected, in short-term memory. It is by virtue of the perceiver’s “schematic map” that he is able to integrate a number of fixations. Hochberg (1968) defined a schematic map as “a program of possible samplings of an extended scene and of contingent expectancies of what will be seen as a result of these samplings [p. 3231.” Although Hochberg’s definition of a schematic map differs slightly from other definitions of schema, it is clear that the schematic map is a form of internal representation of the visual world. The subject does not “passively” take in information, but samples the visual world as if he were actively testing his expectancies and were placing successive fragments of visual information into schematic maps. Thus it seems that the initial perception of a form or scene too large to be seen in a single glance is built up over successive fixations. Hochberg (1968) has argued that is is by virtue of a schematic map that the mature perceiver integrates numerous fixations, and Jeffrey (1968) has offered a mechanism for the gradual construction of such schemata. This discussion, by focusing on the role of representations of the visual world, takes us once again to some of the issues discussed in the last section. Where the perceiver looks and how long he continues looking depend partially upon his current knowledge and representations of the visual world and upon his manner of encoding that knowledge.

VII. Speed of Visual Scanning An increase with age in the speed of visual scanning has been found with three types of measures. First, speed has been assessed globally as the time required to complete a search task or a comparison task. On these tasks, the increase in speed could be due to a host of factors, such as a decrease in redundant fixations, an increase in fixations on only the informative portions of stimuli, faster processing within each fixation, a wider field of view within each fixation, etc. Second, the average duration of fixations during visual scanning has been used as an index of speed. Fixation duration is assumed to represent the length of time it takes to process the information being fixated. Finally, the period of time necessary for form recognition between presentation of a visual stimulus and presentation of a mask (assumed to interrupt processing of the stimulus) provides a measure of the speed of visual information processing. The data base for each of the measures of visual scanning speed will be briefly reviewed. In research on the speed of visual search for somewhat familiar forms, letters and words have been used most frequently. Gibson and Yonas (1966a, 1966b) found a decrease from Grade 2 to college in the time required to find a

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target letter embedded in a matrix of letters. And Leslie and Calfee (1971) found a decrease from Grade 2 to college in the speed of visual search for words. The speed of scanning has also been assessed in comparison tasks using alphabetic material. Nodine and Steuerle (1973) and Nodine and Lmg (1971) recorded eye movements while children were comparing graphemes and four-letter pseudowords, respectively. They found a decreasing number of fixations and a decreasing mean fixation time for each letter or word pair with age. Similarly, in tasks where all children were previously unfamiliar with the meaningless figures used as stimuli, Forsman (1967) and Rand and Wapner (1969) found decreases in the time required to solve matching-to-standard tasks. Decreases with age in the mean duration of fixations also suggest an increase in the speed of scanning. Mackworth and Bruner (1970) found that, averaging across sharp, blurred, and very blurred photographs, the mean fixation duration of 6-year-olds was slightly longer than that of adults (adults = 360 msec; children = 373 msec). On the sharp photographs the difference was greater, with children averaging 375 msec and adults 348 msec per fixation. Similarly, but with different age groups, Zinchenko et al. (1963) found a decrease in the mean fixation duration from 3 to 6 years of age during the initial inspection of a form. However, the Zinchenko data again point to the importance of familiarity and task requirements, for the fixation durations increased for the 6-year-olds and decreased for the younger children when they attempted to recognize a previously viewed shape. Age differences in the mean duration of fixations on text have also been reported (Buswell, 1922; Taylor, 1965; Tinker, 1958). For example, Taylor ( 1965) found that mean fixation duration decreased from 330 msec at Grade 1 to 240 msec at college. This decrease is greater than that found for pictorial material and again emphasizes the importance of considering the subject’s experience with visual stimuli. The information-processingliterature offers more precise data on the speed of processing the visual information obtained in a single fixation. In a number of studies subjects have been asked to identify visual targets presented for very brief periods of time. The shorter the mean target duration required for correct identification, the faster the speed of processing the target is assumed to be. These studies (see Table I) have indicated a decrease with age in the mean target duration required for accurate identification of a form (Goyen & Lyle, 1971; Haith, Morrison, & Sheingold, 1970a; Munsinger, 1965). In addition, a series of studiesbyBraine(Braine, l968,1972;Ghent, 1960;Ghent &Bernstein, 1961)has indicated an inverse relationship between age and the tachistoscopic exposure duration required for 50% correct recognition (see Table II). However, because the initial internal representation of information provided by light hitting the retina can persist after termination of a brief exposure for between .300 and 1.5 sec (Mackworth, 1963; Posner, Boies, Eichelman, &

TABLE I

STUDIES OF THE SPEED OF PROCESSING SINGLE STIMULI WITHOUT A MASK Author (s)

Subjects

Stimuli and response

Goyen and Lyle (1971)

7.3-8.3 years; 8.5-9.5 years; normal and retarded readers at each age

Rectangular shapes resembling contours of 4-letter words; recognition by pointing

10 msec

4 years; 5 years; adults

Geometric forms; recognition by pointing

5,10,20, and 30 msec for adults; 10,20, and 30 msec for children

Haith e l al. (1970a)

Munsinger (1965)

4.5-5.0 years

(n=4);

adults

Random shapes of 5 or 20 independent turns; recognition by pointing

Target duration

Varied durations

Results The younger, retarded readers were less accurate than the other three groups of subjects

Adult performance was above 50% accuracy at 10 and more rnsec. The 5-year-olds were less accurate than adults at 10 msec, and the 4-year-olds were somewhat less accurate than adults at 10, 20, and 30 msec The exposure duration required for a recognition accuracy of 40-95% ranged from 5 to 18 msec for adults and from 80 to 400 msec for children

P 5

4

g

k c1

1'

2 ! i rn

B

3. m

TABLE I1 TACHISTOSCOPIC EXPOSURE DURATIONS REQUIRED FOR 50%CORRECT rnCOGNITION

~~

~

Author (s)

Target

Ghent (1960)

Outlined realistic figures

Ghent and Bernstein (1961)

Geometric figures

Age or grade 3 years 4 years 5 years 6-7 years

3 years 4 years 5 years

Exposure duration in msec for each age group Median Range 100 20-500 20 10-200 5 5-40 5-40 5 100 20 5

10-500 3- 100 3-20

Braine (1968)

A:

Rectilinear figures

Grade 3 Grade 5 Grade 7 College

120 60 36 12

36- 120 12- 120 12- 120 12-24

B:

Binary patterns formed by a row of 8 circles with 2 or 3 circles blackened

Grade 5 Grade 7 College

120 60 24

24- 120 24- 120 24-24

Braine (1972) A: B:

Rectilinear figures Simpler rectilinear figures than in A

6.8 years 3.1-3.9 years 4.0-4.4 years 4.5-5.1 years

3.3- 100 msec 40-200 20-100 10-100


-HMask

F;z~;on

179

SUBJECT

REPORT

Interstimulus interval (ISI)

Stimulus onset asynchrony (SOA) : Equal to target duration t IS1

Fig. I . Sequence of events for a typical tachistoscopic task investigating speed of processing. The

IS1 (or SOA) is typically varied within the experiment to allow different time intervals for encoding the target(s).

Taylor, 1969; Sperling, 1960), an accurate assessment of processing speed requires that the duration of the initial representation (or “short-term visual store”) be controlled. A patterned mask, occurring at specified intervals after target presentation, has frequently been used to interrupt the processing of the stimulus (Haber & Standing, 1968; Kahneman, 1968; Liss, 1968). Figure 1 presents the sequence of events for a typical tachistoscopic study of information processing speed where a visual mask is used. In the “typical” experiment the subject is presented with a target for a certain period of time, and a mask is presented at various intervals after target presentation. The stimulus onset asynchrony (the interval of time between target onset and mask onset) appears to be the time interval of importance for identification accuracy, although a number of studies have reported data in terms of the interstimulus interval (the interval of time between target offset and mask onset). A direct comparison of the time intervals used in the various developmental studies is not feasible because of differences across studies in both experimental procedure (e.g., target duration, mask duration, stimulus onset asynchrony, target complexity) and dependent variables (e.g., threshold for incorrect identification, proportion of items correct at a specific interstimulus interval or stimulus onset asynchrony). In addition, several variables other than speed of processing, such as fatigue, the ability to construct a figure from partial information, and the ability to identify a figure in a noisy array, could influence results on these tasks. Fortunately, most of the studies tried to control for some of these possibly confounding variables. With these limitations in mind, an attempt has been made to identify the developmental trends within each study and then to assess their consistency across studies. Table I11 presents the details of the studies in which the speed of processing single forms was investigated using a mask to control the duration of the initial visual image.

TABLE I11

m D I E S OF THE S E E D OF PROCESSING A SINGLE nIMULUS WITH A MASK ~

Author (s)

~

~~

~~

~~

Stimuli and response

Subjects

Target duration; Stimulus Onset Asynchrony (SOA)

Results

Metacontrast and discrimination of succession Pollack (1965)

7 , 8 , 9 , and 10years

Thor (1970)

Normals: 7.0, 9.8, and 13.8 years; retardates: CA = 16 years, IQ = 62.3

~

Mid-gray disc and a white-ring mask presented successively; verbal report of target visibility

Targets for 12 msec; SOA’s from 12 to 262 msec

The mean stimulus onset asynchrony (SOA) required for target visibility decreased with age from 172 to 117 msec

Two black squares presented successively; verbal report of 1 or 2 squares

Targets for 10 or 30 msec; SOA’s varied using method of limits

The mean SOA required for discrimination of succession decreased with age. Retardates and 9.8-year-olds performed comparably

Target identification with mask Blake (1974)

4.8 and 8.5years, adults

Outlined forms; recognition by pointing

Targets for 30 msec for 4-yearolds and for 15 msec for 8-year-olds and adults

The mean number of correct responses increased with increases in the SOA up to 165 and 180 msec; no significant differences were found among age groups

Bosco (1972)

7 , 9 , and 12 years

Liss and Haith (1970)

4-5,9-10 years, adults

Geometric forms; not stated by author Horizontal and vertical lines; recognition by pointing

Target for 5 msec; SOA’s from 5 to 125 msec Target for 20 msec; SOA’s from 20 to 170 msec

The mean SOA required for target identification decreased with age With both forward and backward masking the mean SOA required for target identification decreased with age. The absence of an age

masking interaction indicated no age differences in speed of target identification X

Gummerman and Gray (1972)

Grades 2 , 4 , and 6, adults

Capital T rotated 90” to left or right; verbal report of left or right

Target for 80 msec; mask presented immediately on offset of target

Children in Grades 2 and 4 made fewer correct responses than Grade 6 children and adults

L. K. Miller

8 and 12 years, adults

Capital letters D, 0, and S; verbal report of letter

Target for 30 msec; SOA’s from 0 to 90 msec

Identification accuracy increased with age over all SOA’s. Although a nonmonotonic function relating performance and SOA was found for the two older groups, performance of the 8-year-olds was low at all SOA’s

H. H. Spitz and

Normals: 9.8 and 15.O years; retardates: CA= 16, IQ=63.8

Capital letters D and 0; verbal report of letter or “nothing”


The 15-year-old normals made more correct responses than the other two groups. The percentage correct responses increased as a monotonic, negatively accelerated function of SOA

Welsandt e t al. (1973)

5 , 1 0 , and 16 years, adults

Capital letters E, H, K, and X;verbal report of target target


All age groups increased in accuracy

(1972)

Thor (1968)

m c

with longer SOA’s, but age differences occurred at the longer SOA’s From 83 to 153 msec, 5-year-olds were least accurate From 8 3 to 133 msec, 10-yearolds were less accurate than 16-year-olds and adults

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The data from all but two of the studies reviewed indicated a decrease with age in the stimulus onset asynchrony required for recognition of a single target (Bosco, 1972; Gummerman & Gray, 1972; Miller, 1972; Pollack, 1965; H. H. Spitz & Thor, 1968; Thor, 1970; Welsandt, Zupnick, & Meyer, 1973). Blake (1974) found no age differences in the speed of processing a single shape, though the significance of a 15 msec longer presentation time for Blake’s youngest subjects is Lnclear. Liss and Haith (1970), who used the simplest stimuli-horizontal and vertical lines, also found no significant age differences. It is possible that children process very simple stimuli as rapidly as adults but process “complex” or “confusable” stimuli more slowly than adults. Further studies which vary target “complexity” or “confusability” in a within-subjects design are needed to test this hypothesis. The speed of processing multiple-form arrays has been investigated using tasks which require subjects to locate a particular target in a multiple item display. Miller (1971, 1973) and Liss and Haith (1970) found that older subjects were able to locate targets at shorter exposure durations than younger children. In addition, Blake (1974) and Haith et al. (1970) have investigated age differences in the time required for shape recognition in arrays of different sizes. They reported that, compared to older children and adults, 4- and 5-year-olds were progressively slower as array size increased. These data will be discussed in more detail in Section VII. Thus, in general, the information-processing literature suggests an increase with age in the speed of processing the information available within a single fixation. These small differences in speed could, when accumulated over numerous fixations, contribute to significant age differences in visual scanning speed, but it seems unlikely that they are totally responsible for speed differences on extended search tasks. Indeed, L. K. Miller (1973) attempted to relate performance in a single fixation to performance across multiple fixations and found, using two different models, “that the predicted rate of performance increase [with multiple fixations] is much faster than that actually found, the fit being especially poor for the youngest subjects [p. 2511.” Miller’s youngest subjects were in Grade 1. Therefore, it seems that additional factors come into play on multiple-fixation tasks when peripheral information may be used for directing the next saccade and when information may be integrated across glances.

VII.

Field of View

Data on developmental changes in the field of view and in the use of peripheral information are ambiguous, but the significanceof such changes, if they do exist, warrants their discussion. The useful field of view has been defined as “the area around the fixation point from which information is being temporarily stored and


I83

then processed during a visual task [Mackworth & Bruner, 1970, p. 1581.” The field of view is influenced by two primary factors. Although these factors can be considered separately, they are often functionally related in visual scanning. One factor is the “amount” of visual information present in a field of a specified visual angle, where “amount” may depend upon both number of items and characteristics of items (e.g., complexity, confusability). For example, Mackworth (1965) found that the addition of extra letters to a stimulus display seriously impaired the ability of adults to accurately compare three letters; he concluded that “visual noise causes tunnel vision.” The other factor is the retinal location of the visual information. The fovea of the retina, which covers approximately 2” of visual angle, enables the resolution of fine detail. Visual acuity drops off rapidly and continuously in the area outside of the fovea, the peripheral retina or periphery (Kerr, 1971; Riggs, 1965). During visual scanning the eyes move in fast jumps called saccades, with fixations being directed toward “informative” portions of the visual display (Gould & Dill, 1969; Mackwolth & Morandi, 1967) so that these portions fall upon the fovea. The nonrandom placement of the fixations indicates that the periphery provides information which is used to guide subsequent eye movements. Furthermore, it has been shown that peripheral processing reduces the time required for foveal processing after an eye movement (Sanders, 1963). Both of these factors-the amount and the location of visual information-play a role in visual information processing and visual scanning. Mackworth and Bruner (1970) presented data on the scanning patterns of 6-year-olds and adults which suggested that children have smaller useful fields of view than adults. They found that, while inspecting photographs, children made considerably more shorter steps (eye movements of .5 to lo) than adults. The number of short steps and the number of longer saccades made by the children did not change as a function of the sharpness of the pictures, whereas the number of short steps made by adults increased and the number of longer saccades decreased on the blurred pictures. Thus the adults appeared to use peripheral visual information to direct their saccades more frequently and more flexibly than children. Mackworth and Bruner noted that the children seemed unable to ‘‘examine details centrally and simultaneously monitor their peripheral fields for stimuli which might be candidates for closer inspection [p. 1721.” Mackworth and Bruner offered several possible reasons for these differences, but the one they favored was that “children have greater difficulty than adults processing the visual data” and thus have a smaller useful field of view. But they did not spell out the mechanism mediating the child’s smaller field of view, although they implied a limited-capacity visual processing system. With an overload of information, the field constricts to allow processing of those items nearer the fovea. The constriction of the field of view would result in shorter interfixation distances.

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Other data are consistent with the notion that less information is required to “overload” children than to “overload” adults. Haith et af. (1970b) and Blake (1974) reported age changes in short-term memory for several shapes presented tachistoscopically. Four- and 5-year-olds were able to report accurately no more than two shapes whether two, three, or four were presented, whereas the number of shapes accurately reported by adults increased as the array size increased to four. Furthermore, Blake found that Cyear-olds took longer to process two items in a four-item array than in a two-item array, and the performance of 4-year-olds was quite adversely affected when selective processing was required, i.e., when they were asked to report the items in two specificlocations of the four-item array. Holmes (1972), also, has provided some evidence that children may be less able than adults to simultaneously process a foveal and a peripheral shape, although her data were somewhat equivocal. Possible explanations for these findings may be that, compared to the adult, the child has less total processing capacity, or that more of the child’s total capacity is required for processing each item, or that the child is less able to process shapes in parallel (for discussions of processing models, cf. Blake, 1974; Haber, 1969; Norman & Rummelhart, 1970). Apparent constriction in the field of view is an important issue in visual scanning because such “tunnel vision” would limit the extent to which eye movements could be guided by the peripheral location and the initial processing of stimuli on the retina’s periphery. Sanders (1963) has suggested that the complexity of a perceptual task may have a determining influence on the visual angle at which that task can be performed. Sanders distinguished among three levels of the functional visual field: the stationary field, where competent performance is achieved by peripheral viewing; the eyefield, where eye movements are necessary to supplement peripheral vision; and the headfield, where head movements are also required. Such factors as discriminability of signal and number of signals presented simultaneously affect the display angle at which adults changed their selective strategy from one field to another. Sanders suggested that the visual field transitions, especially the eyefield-headfield transition, may provide a criterion of “perceptual load,” meaning the “difficulty of a largely mental task [p. 1681.” Sanders’ analysis is consistent with the interpretation that children have restricted fields of view in that the same material may present a processing load which is relatively greater for children than for adults. The other factor, retinal location of the presented information, is definitely important for the acuteness of vision, and the finding of smaller useful fields of view in children may be based partially on age differences in peripheral acuity. In two studies with adults (Erickson, 1964; Johnston, 1965) a positive relation between peripheral acuity and the speed of visual search was found. To the extent that the peripheral acuity of children is less than that of adults, we might expect shorter interfixation distances and longer over-all search times. Research on the adult peripheral visual system is limited, but research on age changes in peripheral functioning is almost nonexistent. Lakowski and Aspinall


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(1969) found that the retinal sensitivity of children between 6 and 11 years of age (with n at each age ranging from 1 to 3) increased, with the most dramatic increase found in peripheral sensitivity. However, the few Ss and the problems involved in using standard techniques of visual perimetry with young children (Harrington, 1964) make these findings inconclusive. Holmes (1972), presenting outlined shapes at 1, 2, 4, and 6” of visual angle, found that adults outperformed 5-year-oh and that recognition accuracy decreased as visual angle increased. However, no interaction between age and distance was found except under conditions of weak illumination and little practice. Miller (1969) investigated age differences in peripheral functioning by recording the latency of saccadic eye movements to peripherally-presentedtargets. He found that the latency was greater for 8-year-olds than for 20-year-olds. Furthermore, for children but not for adults, eye movement latencies increased as the target light moved farther into the periphery. The only researcher to use a visual search task to assess age changes in the field of view was Miller (1971, 1973). In his first study, Miller (1971) asked 8-, 1 I-, and 2Gyear-olds to search an array of letters for a target letter located at various distances from the fovea. While the accuracy of target location increased with age and decreased with target distance, Miller found no interaction between age and target distance. In a second study Miller (1973) used a larger display, which subtended 20” of visual angle and which required eye movements for a thorough scan. Exposure duration was varied from 250 to 2000 msec. Once again Miller found little indication of an interaction between age and target distance. He interpreted his data as evidence for age differences in the speed of information processing. However, the tasks Miller and Holmes used to investigate tunnel vision are qtite different from Mackworth and Bmner’s (1970) picture inspection task on which chiidren had shorter interfixation distances than adults. The former tasks do not embody the types of regularities normally encountered in the visud world. It may be primarily in situations where expectancies about the visua1 world can influence performance that the greatest difference exists between the child’s and the. adult’s fields of view. In these more realistic situations the adult may be able to infer more from less perceptual information than can the child as a function of the richer development of the adult’s representations and expectancies concerning the visual world (cf. Wohlwill, 1962). Indeed, Hochberg (1968) has argued that “the effects of perceptual learning consist of changes in where you look, and of how you remember what you saw, but not of changes in what you see in any momentary glance [p. 3261.” Morrison’s (1971) and Sheingold’s (1973) findings that children differed from adults not in the amount of information initially represented in the short-term visual store but in the subsequent encoding and rehearsal processes, are consistent with this position. Virtually no systematic research has been directly focused on the use of peripheral information for the direction of subsequent eye movements. The

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normal visual environment, and printed text, present certain regularities which a viewer may detect peripherally and use to govern his eye movements. As Hochberg (1972) has noted:

. . . the content of each glance is always, in a sense, an answer to a question about what will be seen if some specific part of the peripherally-viewed scene is brought to the fovea. In viewing a normal world, the subject has two sources of expectations: (i) he has learned something about what shapes he should expect to meet with in the world and about their regularities; and (ii) the wide periphery of the retina, which is low in acuity and therefore in the detail that it can pick up, nevertheless provides an intimation of what will meet his glance when the observer moves his eyes to some region of the visual field [p. 651. Research is needed which assesses the child’s use of the periphery with realistic scenes as well as with other types of stimuli, and in situations where the child’s knowledge of what peripheral information is significant is controlled or systematically varied. Mackworth and Bruner (1970) found that children’s long saccades sometimes ended on areas of high contrast, whereas adults’ saccades did not land on high-contrast areas unless they were also informative. Also in contrast to adults, children did not vary their number of saccades as a function of the sharpness of the photographs. Thus there do appear to be differences either in the flexibility with which children use peripheral information or in the actual peripheral information they use.

VIII. Summary Visual scanning, the process by which information is sequentially acquired from the visual environment, reveals several functionally interrelated changes during childhood. These age-related trends in visual scanning provide evidence concerning changes in the child’s expectations about what aspects of the visual environment are important and in his strategies for acquiring visual information. Although the trends discussed here were drawn from the literature on visual scanning, it is significant that the first five of the developmental trends which were discussed can also be induced from the literature on haptic exploration. The parallels in the visual and haptic modalities support the position that central, cognitive processes play a directive role in the acquisition of perceptual information. The six developmental trends which were identified are recapitulated below. With age children demonstrate more systematic, task-appropriate strategies for acquiring visual information. Sequential encounters with visual stimuli are termed systematic when a consistent, task-appropriate relationship can be seen among the individual responses of the sequence. Tasks on which children are asked to name the items in an array and comparison tasks indicate that children can perform systematicallyon simply patterned arrays before they can on random or matrix arrays. Thus children are able to use the contour of an array to guide


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systematic performance before they are able to impose a pattern on an array. Only in the latter case can it be inferred that an internally-generated strategy is primarily responsible for systematic performance. With age children show an increasing ability to maintain optimal performance across variations in the content and arrangement of stimuli. Younger children, relative to older children and adults, have more need of context support for systematic scanning, and their scanning is more vulnerable to context interference, i.e., to disruption by particular stimulus attributes or task-irrelevant visual information. With age children’s visual scanning becomes more exhaustive and more efficient. On comparison and matching-to-standard tasks the scope of children’s scanning becomes more task-appropriate; it becomes more exhaustive or more efficient as required to meet task demands. Also, the initial inspection of outlined figures or visual scenes becomes more exhaustive with age. With age there is an increasing focus on the portions of visual stimuli which are most informative for the specific task. If visual scanning is viewed as a purposive search for information, it is obvious that the subject must know what information is significant for a specific task before he can focus on the “informative” aspects of stimuli. The information a subject seeks is probably a function of a number of factors, including his comprehension of the task requirements, his knowledge of the visual environment, his strategies for encoding that knowledge, and his more general cognitive ability. Another factor-the ability to attend selectively to the informative aspects of stimuli when those aspects are known-also appears to be important. With age there is an increase in the speed of completion of visual search and visual comparison tasks. Data on fixation duration and the identification of tachistoscopically-presented stimuli suggest that with age the child can more rapidly encode the information present within each fixation. Nevertheless, it is likely that additional factors, such as the ability to integrate information rapidly across glances or to pick up information farther into the periphery, affect speed on tasks requiring multiple fixations. The sixth trend is more ambiguous than the preceding ones, but some data suggest that with age the size of the useful “field of view” increases. Three factors may possibly contribute to the apparent expansion of the field of view. The child’s smaller field of view may be based partially on a constriction in the field with an “overload” of information and the same information may represent a greater processing load for children than for adults. The role of peripheral acuity and peripheral processing, independent of processing load, is currently unclear. The child’s lesser-developed ability to sample wisely and to infer from limited perceptual information may also contribute to age changes in the field of view. Throughout this review the significanceof familiarity with the stimuli has been evident. With increasing familiarity subjects learn which stimulus features are likely to be informative or distinctive for particular purposes. Furthermore, with

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increasing familarity it appears that subjects form an internal model (an image, a schema) of the visual stimulus, which then influences subsequent visual scanning. With an unfamiliar stimulus which cannot be readily assimilated to an existing schema, there is a sequence from only a few fixations on salient details, to more exhaustive scanning of the visual stimulus, and then again to fixations on only a few details. The “microgenetic” sequence from limited to more exhaustive scanning of an unfamiliar visual stimulus roughly parallels the ontogenetic sequence typically found in the initial scanning patterns of children and adults confronted with a visual stimulus. These six main trends point to two major dimensions on which age changes occur. One dimension refers to the systematicity of the acquisition of visual information-to the how or the form of information acquisition. With age, the child appears increasingly able to conduct a task-appropriate, systematic, and exhaustive scan which is less vulnerable to disruption by irrelevant particularities of the visual field. The second dimension refers to the child’s growing knowledge about the “informative” aspects of the visual stimuli he encounters and his increasing focus on these aspects of the visual environment. This dimension refers to the what or the content of information acquisition. The research on changes in the scope and locus of fixations with familiarity and age and on the apparent increase in the field of view point to the importance of the child’s representations of and expectancies concerning the visual world. Both of these dimensions-form and content-reflect the child’s cognitive capacities and his representations of significant regularities in the visual environment.

ACKNOWLEDGMENTS The author would like to thank Joan S. Bissell, Karen M. Cohen, Deborah K. Walker, and Sheldon H. White for their encouragement and for their constructive comments on several previous versions of this paper.

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