The acquisition of abstract letter codes

JOURNAL

OF EXPERIMENTAL

CHILD

The Acquisition CARL

E. MCFARLAND,

PSYCHOLOGY

of Abstract

JR., TRUDY

(1978)

25.437-446

Letter Codes

J. FREY,

AND JAMES

M. LANDRETH

University of Alabama in Birmingham A modification of Posner’s letter-matching paradigm proposed by Belier (1971) was employed to study the development of abstract visual and name codes for letters. Second-, fourth-, and sixth-grade students (ages 8, 10, and 12 years, respectively) were presented in advance one of a pair of to-be-matched letters. Case agreement (upper- and lowercase) between the prime letter and the letter pair was manipulated to differentiate facilitation based on concrete features of the stimulus letter from that based on the letter’s abstract visual code. For physical matches second graders showed greater facilitation from same-case primes than from different-case primes, whereas sixth graders benefited equally from both types of prime. For same-name and different conditions, no qualitative developmental differences were revealed as all subjects benefited from letter primes irrespective of case agreement. The acquisition and utilization of abstract visual codes for letters are a later acquisition than name codes, which were clearly operative at the lowest grade level in the present experiment.

The essentially infinite number of physically or conceptually distinct events in the world makes it impossible to process each of them as functionally different. The most significant question arising from this axiomatic realization is: How do clearly nonidentical events come to be treated as equivalent? The present research deals specifically with development of the classificatory skills exhibited by adults in letter recognition (e.g., Posner, 1969; Posner, Lewis, & Conrad, 1972). Consider the letter A. It can assume many different visual forms (e.g., A, JB, a, a) and it receives various phonetic treatments; nonetheless, all manifestations of this symbol are regarded as instances of the same thing. This common act of categorization occurs when external input (visual or auditory) comes into contact with a previously estabhshed internal system. Unfortunately, no one knows how this operation works. Posner (1969) has proposed an abstract code for letters, as well as other habitual stimulus events, that This investigation was supported by a University College Research Grant from the University of Alabama in Birmingham to the first author. The authors are grateful to Mrs. Joyce McCollum, Dr. William Eddins, and Dr. Lloyd Engdahl of the Mountain Brook Board of Education for their generous support throughout this project. The authors also wish to thank Chong Sook Suh and George Kellas for their comments on an earlier draft ofthis paper. Requests for reprints should be sent to Carl E. McFarland, Jr., Department of Psychology, University of Alabama in Birmingham, Birmingham, AL 35294. 437

0022-096517810253-0437$02.00/O Copyright 0 1978 by Academic Press. Inc. All rights of reproduction in any form reserved.

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serves as an efficient mechanism for combining past and present input. If such a proposal has psychological reality, the child’s acquisition of this abstract level for overlearned symbols would be one of considerable consequence. Furthermore, it should be possible to identify experimentally the chronology of this acquisition. The present study was primarily an attempt to obtain data that would both identify the approximate age of acquisition for abstract letter codes as well as provide information on the nature of these codes. Considerable empirical evidence has accumulated that indicates humans have a propensity for abstracting redundant information from their environment to form internal representations that are sensitive to the commonalities among pattern classes (Attneave, 1957; Franks & Bransford, 1971; Posner & Keele, 1968). One implication of this work is that the efficiency of human information processing might be due partly to the fact that overlearned stimulus patterns need not be stored on each occasion. Instead, these patterns would simply activate the corresponding internal prototypes abstracted from previous experience and thereby reduce information processing and storage requirements. Some evidence for abstract letter representations was provided by Beller (1971), who employed a modified version of Posner’s letter-matching task. In the original task (Posner & Mitchell, 1967) subjects were shown a pair of letters simultaneously and required to decide rapidly whether they were the same or different. The major finding was that a “same” response to physically identical letters (e.g., AA) typically required 80- 100 msec less time than a same response to letters having only a name in common (e.g., Aa). Posner (Posner, 1969; Posneret al., 1972) has argued convincingly that this result, viewed in conjunction with several converging operations, indicates that the physical (visual) code and the name code represent two isolable processes that operate, to some extent, in parallel. The naming process is not initiated until the visual process is already underway. Apparently the codes arising from different levels of processing do not obliterate previously established codes. It is generally accepted that physical-identity matches (AA) can be made entirely on the basis of the visual code, whereas same-name matches require access of the name code. Beller (1971) “primed” subjects by presenting in advance one of the pair of to-be-matched letters. The prime significantly reduced RT (reaction time) for both physical and same-name matches. Beller suggested that, whereas the name-match facilitation resulted from the prime placing the appropriate letter name in active memory, the physical match must have benefited from the subject’s automatic use of the advance information to construct an internal representation that anticipated the actual stimulus pair. Two additional results reported by Beller (1971) are especially pertinent to the present experiment. In Experiment II the prime was shown to be effective even under strict physical identity instructions in which the array

ABSTRACT

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AA required a “same” response while Aa required a “different” response. This result indicated that at one level of processing the cognitive representation activated by the prime was specifically visual in nature and that a letter prime could facilitate a match independent of its name code. In Experiment IV, a post hoc comparison revealed that physical match RT was reduced equally by letter primes presented in the same and opposite cases of the array; that is, if the prime was A, the pairs aa and AA were facilitated. This effect was shown to obtain when the case relationship between the prime and the letter pair was totally predictable (Experiment III) and when it was unpredictable (Experiment IV). As Rosch (1975) has suggested, this result is important because it indicates that the facilitative effect of the prime is not due to a maintenance of the prime’s physical features, but instead to an abstract representation generated by subjects regardless of the physical form of the prime. It is also important to note that the significant facilitation induced by the prime, irrespective of the predictability of the prime-stimulus pair case relationship, emphasizes the automatic strategy-free nature of the letter prime’s influence. In reference to this problem, Posner (1973) has argued that “it is an increasingly common view that the processes of input coding are not much subject to the attentional control of the subject. At this level of processing it is often more difficult to avoid the occurrence of a highly overlearned association than it is to achieve it” (p. 38). In the present experiment, children from the second, fourth, and sixth grades participated in a letter-matching task with same-name instructions. Case agreement between the prime and the letter-pair array was varied systematically to test directly the nature of the representation generated by the prime. The age variable allowed an assessment of the developmental aspects of the abstract visual code for letters. If considerable experience were necessary to form permanent abstract codes, the youngest group of children would be unable to benefit from abstract letter representations as adults apparently do. Moreover, given that the physical match RT for these children would be shortened through priming, we predicted that such facilitation would be based on concrete visual features. If this prediction is an accurate one, second graders should demonstrate priming facilitation on physically identical pairs only when there is case agreement between the prime and the array. Opposite case primes should either provide no facilitation or possibly inhibit the physical match (cf. Posner & Snyder, 1975). Based on Beller’s (1971) findings, prime facilitation should be independent of prime-array case agreement for the older children. The main purpose of the present investigation was to provide support for the hypothesis that physical-identity matching based on abstract visual codes and employed by experienced readers is preceded in development by a stage in which young readers base these matches on concrete visual features.

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A secondary purpose of the present study concerns the age-related priming effects for same-name matches (Aa). If successful priming of a same-name match requires activation of a name code that equals the visual code in complexity, degree ofabstraction, and reliance on experience, then the younger children might not benefit from the prime when matching on the basis of name identity. Matches at this level could not be facilitated by simple retention of the physical features of the prime as could physical matches; that is, matching for name identity cannot occur at the level or mode of processing in which the prime is represented. Therefore, priming might prove to be ineffective for same-name matches performed by second graders regardless of the physical form of the prime or the array. On the other hand, if priming for same-name pairs involves the comparatively simple operation of placing a letter name into active memory, then even the youngest children would benefit from the prime. METHOD

Subjects. The subjects were 36 public school children, 12 from each of the second, fourth, and sixth grades. The age ofthe children was 7 years, 10 months (SD = 3.5 months): 9 years, 9 months (SD = 5.3 months); and 12 years, 2 months (5’0 = 4.2 months) for the three grades. At each grade level, half of the subjects were male and half female. Stimulus material. The stimuli were the upper- and lowercase letters A, B, D, E, G, H, I, M, 0, S, T, V, X, Y, and Z. These letters were selected on the basis of their visual clarity when typed with a Smith-Corona 2200 typewriter mounted with Primatype typeface. A test stimulus set of 108 letter pairs was constructed containing 30 physically identical pairs (e.g., AA, bb), 30 nominally identical pairs (e.g., Aa, bB), and 48 different-letter pairs (e.g., AB, ba, Ba, aB). The 30 physically identical pairs were formed by employing both cases of each of the 15 letters (e.g., AA, aa). For the 30 nominally identical pairs, case order was simply reversed (Aa, aA). The 48 different-letter pairs were constructed by randomly pairing letters with the restriction that no two pairs would be the same; an attempt was made to employ all stimulus letters as equally often as possible. Three different random sequences were developed using these 108 stimulus pairs. Each of the stimulus pairs served once in each of the prime conditions (same case, different case, unprimed) across the three sequences. Within each sequence, one-third of the stimulus pairs representing a particular pair type (e.g., physically identical) were paired with same-case primes, one-third with different-case primes, and one-third were unprimed. Type of prime was manipulated by employing a prime letter that was either identical to the first letter of the stimulus pair (same case) or presented in the opposite case (different case). A prime was never totally misleading: each prime always shared at least a nominal identity with the first letter of the stimulus array.

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For example, A could serve as the prime for AA, aa, Aa, aA, Ab, ab, but would not serve as the prime for BA, Ba, BB, or bB. This arrangement was intended to offer the children some incentive to attend to the prime on each trial since the prime always supplied some information relevant to the current match. For unprimed trials, the prime letter was replaced by a row of three asterisks. Apparatus. The experiment was conducted with an Iconix four-channel tachistoscope. Letter pairs were typed on 6 x 9 in. white cards using a Smith-Corona 2200 typewriter and Primatype typeface. The letters constituting a stimulus pair were positioned horizontally and subtended a visual angle of 1.2 degrees. Letter primes and asterisks were typed individually on separate cards. Response buttons attached to microswitches were placed directly in front of the subject. For half ofthe subjects at each grade, the response button on their dominant side was labeled ‘bsame” and the button on their nondominant side was labeled “different.” These conditions were reversed for the remaining subjects. Height differences among the children were accommodated with an adjustable subject chair. Design and procedure. A 3 x 3 x 3 mixed design was employed. The within-subjects factors corresponded to type of letter pair (physical, same name, and different), and type of prime (same case, different case, and unprimed). Grade level (second, fourth, and sixth) represented the between-subjects factor. Prior to participation in the experiment, each subject was given instructions to ensure that he would understand clearly that the prime always predicted at least one letter of the stimulus pair to follow. Subjects were also made aware of the variable case relationship between the prime and the letter pair. This procedure was employed to induce the children to attend to all letter primes. Subjects were randomly assigned to each of the three test sequences such that four subjects at each grade level received each sequence. The experiment consisted of two 35min sessions run on consecutive days. During the first session, subjects were given 30 practice trials followed by 40 experimental trials. On the second day subjects received 20 practice trials followed by 68 experimental trials. To initiate each trial the subject pressed afoot switch which presented the prime for 1500 msec, followed by a fixation box that appeared for 1000 msec, which in turn was replaced by the letter pair. The subject was instructed to respond “same” if the members of a stimulus pair had the same name (Aa, AA) and “different” if they had different names (AB, Ab). Depression of either response button removed the stimulus from view. The subject was asked to attend carefully to the prime letter and to respond as quickly and accurately as possible. There was an approximate 15set delay between trials.

442

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FREY.

AND

LANDRETH

RESULTS

The predictions of interest in the present study concerned the differential effects of type of prime as a function of grade level within the physically identical, same-name, and different conditions, rather than the specific differences between these conditions. For this reason, responses to the three match conditions were analyzed separately. A 3 x 3 mixed analysis of variance was performed on the mean RT for correct responses for each type of match. The factors corresponded to Type of Prime and Grade Level. We will consider first the results for the physically identical condition. The analysis demonstrated that RT for primed trials was shorter than RT for unprimed trials, F(2,66) = 33.77, p < .OOl, and that RT decreased as Grade Level increased, F(2,33) = 6.12, p < .Ol. However, these effects are qualified by a significant Type of Prime x Grade Level interaction, F(4,66) = 2.96, p -=c.05. This interaction can be observed in the left panel of Fig. 1. The graph clearly shows that case agreement between the prime and the letter pair was a potent variable for second graders but had no observable effect on physical match RT for sixth graders. To substantiate this observation, simple main effects analyses were conducted on the data from two levels of the Type of Prime factor (same and different case) for each grade level. Same-case primes proved to be more facilitative than different-case primes for second graders, F(1,ll) = 15.51, p < .005, and for fourth graders, I 1 PHYSICALLY IDENTICAL

1

SAME NAME

I

I

I

DIFFERENT

Grade Grade

2 4

-. 1c---O----IGrade 6J

TYPE OF PRIME

FIG.

1. Mean reaction time for physically identical matches, same-name matches, and different responses as functions of type of prime and grade level.

ABSTRACT

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F( 1,ll) = 6.5 1,p < .05. However, this effect was absent for sixth graders, F < 1. These results support the developmental prediction made earlier. For second graders, matching required 127 msec longer with different-case primes than with same-case primes, while this difference was 45 msec for fourth graders and only 2 msec for sixth graders. This developmental trend indicates that the disruption caused by discrepancies in visual form decreased steadily with grade level until it disappeared completely by grade six. The graph also shows some facilitation for physical matches from different-case primes even for second graders. It had been predicted that lack of case agreement between the prime and the letter pair might create inhibition for the younger children, but this clearly did not occur. Analyses performed on the mean RT for correct responses for the same-name and different conditions yielded similar results, as is evident in the center and right panels of Fig. 1. In the same-name condition, the main effects for Type of Prime, F(2,66) = 26.90,~ < .OOl, and for Grade Level, F(2,33) = 5.34,~ < .025, were significant. However, it is clear that match time was not affected by the case agreement between prime and letter pair and that there was no indication of a Type of Prime x Grade Level interaction (F < 1) as observed in the physical match condition. Similarly, for different responses, Type of Prime, F(2,66) = 22.73, p < .OOl, and Grade Level, F(2,33) = 7.64,~ < .005, proved significant, but again there was no indication of an interaction (F < 1). It should be noted that responses to both same-name and different-letter pairs require the access of name-code information (Posner, 1969). Apparently, the prime supplied the required name information, irrespective of case agreement, such that both same-name matches and different responses were facilitated equally at each grade level. There appear to be no qualitative developmental differences in either the same-name or different conditions. The error data for all experimental conditions are presented in Table 1. The overall error rate was 6.03%. The most noteworthy aspect ofthese data is shown in the physical-match condition where a greater error rate for different-case primes over same-case primes emerged at grade two. This difference decreased to zero across grade levels. This result complements the corresponding effect present in the RT data. DISCUSSION

Letters are probably the most overlearned stimuli that adult humans process. An individual letter occurs in many different forms as a result of differences in size, curvature, line thickness, tilt, angles, and many additional features depending upon the particular typeface or handwriting; nonetheless, these clearly discernible variations do not play a significant role in reading. This propensity of humans for abstracting away from many of the physical aspects of letters suggests an underlying mechanism that summarizes past experience. We can refer to this mechanism as a schema

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TABLE

1

LANDRETH

MEAN PERCENTAGE ERRORSFOR ALL TREATMENT CONDITIONS

Grade 2 Same case Different case Unprimed Grade 4 Same case Different case Unprimed Grade 6 Same case Different case Unprimed

Physically identical

Same name

Different

2.50 7.50 2.50

8.33 8.33 10.00

7.25 7.91 12.08

2.50 4.17 4.17

7.50 4.17 10.00

5.17 4.83 6.17

3.33 3.33 2.50

5.00

6.67 9.17

4.67 4.67 8.42

or, more specifically, an abstract letter code. While these codes are no doubt operative in adults, it was previously unclear what role they played in the visual information processing of young children whose exposure to printed language is quite limited. The results from the physical-match condition in the present study revealed a developmental trend in which younger children relied heavily on the physical reality of the prime letter, whereas older children appeared to benefit from an abstract code that was activated by an external letter prime, but not dependent on the prime’s physical form. The fact that more facilitation was elicited by same-case primes than by different-case primes, for both second and fourth graders, suggests that the acquisition of abstract visual codes for letters might be based on a considerable amount of experience with printed letters. Although the case-agreement effect is a rather small one for fourth graders, it does conform to the apparent developmental trend. Posner (1973) has argued against Neisser (1967) and Sperling’s (1963) conception of the visual code as a fading stimulus trace followed in a temporal sequence by a name code. Instead, he suggests that a stimulus letter is rapidly assimilated into the letter’s abstract code, an internal representation that is independent of the letter’s name. At this point, the actual physical form of the stimulus letter is irrelevent. The data generated by sixth graders in the present study support Posner’s position in that different-case primes facilitated matches based strictly on visual properties equally as well as same-case primes. The models proposed by Neisser and Sperling cannot accommodate this result. It might appear that these models are descriptive of the second-graders’ performance in that a substantial case-agreement effect was demonstrated. This observation is inadequate for two reasons. First, the different-case primes provide some facilitation

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for the physical identity matches at the second-grade level. Second, the rudiments of abstract letter codes probably exist at this age, but their presence was not revealed by the matching task. In other words, an abstract code must be engraved in the perceptual system deeply enough that it becomes an unavoidable aspect of strategy-independent automatic processing. The acquisition of visual codes for letters appears to be analogous to the child’s acquisition of phonemic distinctions. In learning to comprehend human speech, the child must develop a central concept for each phoneme such that he is capable of ignoring considerable physical variation (allophones) to perceive accurately the speaker’s intended phoneme. However, it should be noted that the development of the phonological system precedes that of an internal graphemic system by several years, just as speech comprehension precedes reading. Furthermore, speech comprehension appears to be an aspect of maturation, whereas reading must be taught (Mattingly, 1972). The results for same-name and different conditions showed that no qualitative differences emerged between the grade levels tested. Priming was equally facilitating at all three grade levels, and, as expected, sameand different-case primes were equally potent since these responses were based on name-code information. These data suggest that intact name codes for letters may well precede their corresponding visual codes in acquisition. This difference might mean that name codes are simpler and require less experience than visual codes. It seems more likely, however, that the name code is acquired earlier as a result of its connection with the phonological system which itself is established early, as indicated above. No direct implications for the psychology of reading can be drawn from the present study. However, extensions of this work may provide some useful information. Gibson and Levin (1975) discuss evidence that indicates that preknowledge of letter names is not a reliable determinant of reading achievement, despite earlier reports of significant correlations of these factors (see Chall, 1967, pp. 141ff.). However, the fact that reading is basically a visual process suggests that the prior establishment of abstract visual codes for letters may be more essential to reading than preknowledge of letter names. It is reasonable to propose that the establishment of visual letter codes might be a source of reader variability. This hypothesis could be tested by employing the present matching task with good and poor readers at different grade levels. Finally, we agree with Posner et al. (1972) that the substantial evidence for an isolable abstract visual processing system is good reason for educators to give special attention to the development of purely visual skills. REFERENCES Attneave,

R. Transfer of experience with a class-schema and shapes. Journal of Experimental Psychology,

to identification-learning 1957, 54, 81-88.

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Beller, H. K. Priming: Effects of advance information on matching. Journal off?perimental Psychology, 1971, 87, 176-182. Chall, J. S. Learning to read: The great debate. NY: McGraw-Hill, 1967. Franks, J. J., & Bransford, J. D. Abstraction of visual patterns. Journal of Experimental Psychology, 1971, 87, 176-182. Gibson, E. J., & Levin, H. The psychology of reading. Cambridge, MA: MIT Press, 1975. Mattingly, I. G. Reading, the linguistic process, and linguistic awareness. In J. F. Kavanagh & I. G. Mattingly (Eds.), Language by earundby eye. Cambridge, MA: MIT Press, 1972. Neisser, U. Cognitive psychology. NY: Appleton-Century-Crofts, 1967. Posner, M. I. Abstraction and the process of recognition. In G. H. Bower & J. T. Spence (Eds.), The psychology of learning and motivation (Vol. 3). NY: Academic Press, 1969. Posner, M. I. Coordination of internal codes. In W. G. Chase (Ed.) Visuul information processing, Academic Press, 1973. Posner, M. I., & Keele, S. W. On the genesis of abstract ideas. Journal of Experimental Psychology, 1968, 77, 353-363. Posner, M. I., Lewis, J., & Conrad, C. Component processes in reading: A performance analysis. In J. F. Kavanagh & I. Mattingly (Eds.), Language by ear and by eye. Cambridge, MA: MIT Press, 1972. Posner, M. I., & Mitchell, R. F. Chronometric analysis of classification. Psychological Review, 1967, 74, 392-409. Posner, M. I., &Snyder, R. R. Attentionand cognitive control. In R. Solso (Ed.),lnformarion processing and cognition: The Loyola Symposium. Potomac, MD: Lawrence Erlbaum Associates, 1975. Rosch, E. Cognitive representations of semantic categories. Journal of Experimental Psychology: General, 1975, 104, 192-233. Sperling, G. A. A model for visual memory tasks. Human Fuctors, 1963, 5, 19-31. RECEIVED:

February 1. 1977:

REVISED:

May 17, 1977.