Processing Time, Imagery, and Spatial Memory

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  • JOURNAL OF EXPERIMENTAL CHILD PSYCHOLOGY 64, 6778 (1997)ARTICLE NO. CH962337

    Processing Time, Imagery, and Spatial Memory

    ROBERT KAIL

    Purdue University

    Measures of cognitive processing time, imagery skill, and spatial memory spanwere administered to 128 8- to 20-year-olds. Age correlated positively with spatialmemory span and accuracy on the imagery tasks but negatively with times on thecognitive processing and imagery tasks. Results of path analyses and structural-equa-tion modeling were consistent with a causal model in which age-related change inspeed of processing is associated with more effective imagery. In turn, imagery isassociated with spatial memory span. Age was also associated with imagery and spatialspan, indicating that other age-related variables need to be incorporated into the causalmodel. q 1997 Academic Press

    Performance on memory span tasks that are verbally based, such as digitspan or letter span, increases steadily during childhood and adolescence. Thischange occurs, in part, because older children and adolescents can articulatedigits and letters more rapidly than young children. Rapid articulation meansthat information is less likely to be lost from working memory prior to recall(Hitch, Halliday, & Littler, 1989). Age-related change in articulation rate, inturn, reflects developmental change in speed of processing information. Thatis, as shown in Fig. 1, age-related increases in processing speed permit morerapid articulation, which, in turn, permit more accurate retention.

    Support for this general view comes from a study by Kail and Park (1994)in which 7- to 14-year-olds and adults were tested on multiple measures ofmemory span, rate of articulation, and cognitive processing time. Age corre-lated positively with a composite measure of memory but negatively withcomposite measures of articulation and processing times. Path analyses indi-cated the following links between the measures: With increasing age, individ-

    The research described in this article was supported by grants from the National Institute ofChild Health and Human Development (HD-19947) and the National Science Foundation (SBR-9413019). I thank Leah Burgy and Laura Curry for testing subjects and two reviewers for theirhelpful comments on a previous draft of this manuscript. Address correspondence and reprintrequests to Robert Kail, the Department of Psychological Sciences, Purdue University, WestLafayette, IN 47907. E-mail: rk@psych.purdue.edu.

    0022-0965/97 $25.00Copyright q 1997 by Academic Press

    All rights of reproduction in any form reserved.

    67

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  • 68 ROBERT KAIL

    FIG. 1. A model showing proposed relations among age, speed of cognitive processing, imagery,spatial span, articulation time, and verbal memory.

    uals executed cognitive processes more rapidly. More rapid cognitive pro-cessing was associated with more rapid articulation, which resulted in moreaccurate recall.

    Spatial memory span also increases with age, but the underlying mecha-nisms are still poorly understood. For example, in Kail (1991), spatial spanwas assessed by asking subjects to recall the positions of Xs appearing in thecells of a 4 1 4 matrix; 10-year-olds recalled an average of 4.0 positionscompared to 5.13 for adults. In Isaacs and Vargha-Khadem (1989), the experi-menter pointed to a set of blocks that were arranged in a random pattern; thechild was to point to the blocks in the same sequence. Span, the longestsequence of blocks that the child reproduced accurately, increased from 4.1at 7 years to 5.6 at 15 years.

    Mechanisms that might mediate the age-related increase in spatial span aresuggested by Baddeleys (1986, 1992) view of working memory, which in-cludes a central executive, an articulatory loop, and a visual-spatial sketchpad,which is . . . a system especially well adapted to the temporary storage ofspatial information, much as a pad of paper might be used by someone trying. . . to work out a geometric puzzle (Baddeley, 1986, p. 109). Informationis lost rapidly from the visual-spatial sketchpad, but this loss can be avoidedif the image is regenerated using visual rehearsal (Juhel, 1991). As illus-

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  • 69COGNITIVE PROCESSING TIME

    trated in Fig. 1, just as the facility with which information is articulatedpredicts performance on verbally oriented tasks such as digit span, the easewith which images are regenerated in the visualspatial sketchpad shouldpredict visual-spatial span.

    Other links are possible. Speed of image regeneration might be related toverbal span, and articulation might be related to spatial span, because subjectsmay recode spatial stimuli verbally (Brandimonte, Hitch, & Bishop, 1992).Speeds of other processes might influence verbal and spatial spans. And, ifspeeds of global and specific processes cannot account for all age-relatedchange in verbal and spatial span, then these constructs would be linkeddirectly to age.

    The aim of the present work was to provide a preliminary evaluation ofthe spatial elements of the framework in Fig. 1, within a path-analytic ap-proach similar to that used in the previous studies of processing time, articula-tion rate, and memory (e.g., Kail & Park, 1994). The study included measuresof cognitive processing time, imagery skill, and spatial span. The primarygoal was to determine the extent to which age-related change in spatial spanwas mediated by processing speed and imagery skill.

    METHOD

    SubjectsThe sample included 112 8- to 16-year-olds, 16 at each of the following

    ages: 8, 9, 10, 11, 12, 14, and 16 years. Their mean ages were 8.18, 9.26,10.25, 11.22, 12.28, 14.35, and 16.25 years, respectively. (Age was sampledmore densely between 8 and 12 years because processing speed changes mostrapidly in these years.) These subjects were recruited via advertisements andpaid $5. Most lived in or near a small city in the Midwestern United States.Also participating were 16 undergraduates at Purdue University (mean age 20.23 years) who participated to satisfy a course requirement. Each groupcontained 8 males and 8 females except at age 8 (11 boys, 5 girls).

    TasksThere were seven measures: three of processing speed, two of imagery

    skill, and two of spatial span.Processing speed. Speed was assessed with variants of existing paper-and-

    pencil tests. The measuresCoding, Number Comparisons, and IdenticalPictureswere selected because each is sensitive to age-related change andeach loads heavily on speed factors in correlational work (Cyphers, Fulker,Plomin, & DeFries, 1989; Laux & Lane, 1985). On the Coding task, fivegeometric figures appeared at the top of the page, each with distinctive linesin the interior (e.g., single vertical line inside a star). The remainder of thepage included 50 empty geometric figures; the subjects task was to draw thecorrect lines. Subjects solved the first five problems for practice, then they

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  • 70 ROBERT KAIL

    FIG. 2. Illustration of the letters task used to assess imagery skill. Subjects first learnedhow uppercase letters were depicted in a matrix like the one on the left (F). Test trials consistedof a lowercase letter at the top of the screen and a matrix with an X in one cell at the bottom.Subjects judged whether the X appeared in one of the cells denoting the uppercase version ofthe letter.

    were timed as they solved the 45 remaining problems. Subjects were askedto respond as rapidly as possible, but not so quickly that they erred.

    In Number Comparisons, 48 pairs of 3- to 12-digit numbers were presented,separated by a dash. In approximately half of the pairs, the numbers in eachpair were identical; in the remainder, they differed by one digit. Subjectsplaced an X on the dash when the numbers in a pair differed. Subjects received18 practice pairs, then were timed as they completed the 48 test pairs.

    In Identical Pictures, each of 24 rows consisted of six pictures. The pictureat the left of each row appeared a second time, with four distractors. Forexample, one problem included a pencil as the first and last picture in a row;distractors included pens, a shorter pencil, and a cylinder. Subjects circledthe picture that matched the first picture. Subjects received 4 practice sets ofpictures, then were timed as they completed 24 sets of pictures.

    Imagery tasks. In the letters task, derived from Kosslyn, Margolis, Bar-rett, Goldknopf, and Daly (1990), subjects first learned the appearance ofuppercase letters (F, J, L) as drawn in a matrix (see Fig. 2). Subjects studiedeach letter for as long they wished, then they were asked to draw the Xs inthe correct cells in the matrix. Training continued until subjects had drawneach letter correctly on two consecutive trials. In the test phase, each trialconsisted of presentation of a lowercase f, j, or l at the top of a computerscreen; appearing below on the screen was a 4 1 5 matrix in which one cellcontained an X. The subjects task was to decide if the cell with the X waspart of the uppercase version of the letter. Subjects responded by pressingone of two keys on a computer keyboard. The computer measured the timebetween presentation of the stimulus and the key press. There were six practicetrials, followed by 36 test problems representing the orthogonal combinationsof 3 letters (F, J, L), 2 responses (uppercase letter overlaps, does not overlap),

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  • 71COGNITIVE PROCESSING TIME

    FIG. 3. Illustration of the lines task used to assess imagery skill. Subjects studied the twolines depicted in the first square, then the two lines depicted in the second square, and, finally,decided whether the lines depicted in the third square represented the composite of the linesdepicted in the first two squares. (The matrix within each square did not appear on the computerscreen; it is shown here simply to highlight the underlying structure of the task.)

    and 6 replications. The mean response time for correct answers was computedfor each subject.

    The lines task was based on Salthouse, Babcock, Mitchell, Palmon, andSkovronek (1990). Each trial had three phases, shown in Fig. 3: subjects (1)studied, for as long as they wanted, two line segments appearing on a computerscreen that connected points in an implicit 4 1 4 matrix, (2) studied a secondset of line segments, for as long as they wanted, and (3) judged whether astimulus was the composite of the previous two sets of line segments. Subjectsresponded by pressing one of two keys on the keyboard; the computer mea-sured response time. Eight practice trials were followed by 36 test trials (18in which the stimulus represented the integration and 18 in which it did not).The mean response time for correct answers was computed for each subject.

    Spatial span. Span was assessed with two tasks, each analogous to conven-tional digit span tasks. In the matrix span task (from Kail, 1991), Xs wereplaced randomly in the cells of a 4 1 4 matrix. In 2 matrices, 2 Xs wereplaced in the 16 cells, 2 matrices contained 3 Xs, and so on, up to 2 matriceswith 9 Xs. Subjects studied a matrix for 5 sec, then recalled by printing Xson a blank matrix. Testing ended when subjects failed to recall both matricesat a given size (e.g., matrices with 4 Xs) perfectly. Matrix span was thelargest matrix that subjects recalled perfectly on both trials.

    In block pointing (from Isaacs and Vargha-Khadem, 1989), nine identicalblocks were placed arbitrarily on a board. On each of two trials, the experi-menter touched two blocks successively, one block per second. The subjectthen attempted to point to the blocks in the same order. If the subject recalledthe sequence correctly both times, then the experimenter pointed to threeblocks, on each of two trials. Testing ended when subjects did not recall theblocks correctly. Pointing span was the largest number of blocks recalledcorrectly on both trials.Procedure

    Tasks were presented in a fixed order (block pointing, matrix span, coding,lines, number comparisons, letters, and identical pictures) so that individual

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  • 72 ROBERT KAIL

    TABLE 1Correlations between Variables

    Variable 1 2 3 4 5 6 7 8 9 10

    1. Age 2. Coding 0.66 3. Identical pictures 0.67 .80 4. Number comparison 0.73 .78 .80 5. Letters RT 0.72 .77 .81 .78 6. Letters accuracy .29 0.27 0.25 0.31 0.32 7. Lines RT 0.49 .64 .71 .61 .70 0.13 8. Lines accuracy .56 0.54 0.55 0.57 0.60 .29 0.35 9. Matrix span .54 0.52 0.52 0.52 0.56 .33 0.45 .47

    10. Pointing span .39 0.31 0.36 0.37 0.42 .28 0.23 .42 .38 M 2.50 70.04 71.58 334.59 3.29 34.17 1.86 29.50 4.00 4.15SD 0.28 19.40 26.69 170.14 0.91 2.05 0.69 4.54 2.07 0.84

    Note. N 128. Age is expressed as the natural logarithm of year; coding, identical pictures,number comparisons, letters RT, and lines RT in seconds; letters accuracy, lines accuracy, matrixspan, and pointing span, in number correct. With df 126, all rs .22 are significant, at p .01.

    differences were not confounded with differences in task order. Testing tookabout 30 min for the youngest children and about 20 for the adults.

    RESULTS

    Errors were infrequent on the three measures of processing time (modesof 0) and were not analyzed. However, errors were more common on themeasures of imagery skill (5.1 and 18.1% for the letters and lines tasks,respectively), so accuracy of performance on these tasks was included in allanalyses.

    Dummy codes were used to calculate correlations involving gender. Theonly significant relation was with block pointing, r .20, df 126, p .05,and indicated that females had higher scores. Gender was ignored in allremaining analyses.

    Shown in Table 1 are correlations for age, processing time, imagery skill,and spatial span. Age correlated negatively with measures of processing timeand response times on the imagery tasks but positively with measures ofspatial span and with accuracy on the imagery tasks. The correlations involv-ing the natural logarithm of age tended to be greater than those involvingunadjusted age; as shown in Fig. 4, this reflects the fact that performancetypically improved more rapidly in childhood than in adolescence. As ex-pected, performance on the two measures of spatial memory correlated nega-tively with times on the processing time and imagery tasks. An unanticipatedresult was that performance on the spatial memory tasks correlated, positively,with accuracy on the imagery tasks.

    The model depicted in Fig. 1 was evaluated in two ways. One involved aseries of multiple regression analyses. For these analyses, composite measures

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  • 73COGNITIVE PROCESSING TIME

    FIG. 4. Performance on the processing time, imagery, and span tasks as a function of age.

    were created for processing time, imagery, and spatial memory span constructsby taking the average of the standard scores for the constituent meas...

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