PROCEDURE FOR ASSESSING VERBAL WORKING MEMORY IN ...

Perceptual andMotor Skills, 1994, 79, 55-64. O Perceptual and Motor Skills 1994

PROCEDURE FOR ASSESSING VERBAL WORKING MEMORY I N NORMAL SCHOOL-AGE CHILDREN: SOME PRELIMINARY DATA I' CYNTHIA A. GAULIN AND THOMAS F. CAMPBELL

Cbildreni Hospitnl of Pittsburgh, Pennsylvania Summary.-A procedure for assessing children's recall of lexical icems m the presence of a competing language task is described. The Competing Language Processing Task was designed to reflect the dynamic processes carried out in workmg memory during language comprehension and production by requiring that the subject hold words in temporary storage while analyzing and responding as true or false to statements. The development of the procedure is described and results of testing of 68 normal chddren ages 6, 8, 10, and 12 years are presented.

Short-term memory, which for decades was considered a system for the temporary storage of information for immediate recall, has recently been conceptualized more broadly as a dynamic system which integrates the storage, retrieval, and processing of complex information. This comprehensive and dynamic system is referred to as working memory and is central to language comprehension and production (Baddeley, 1986). W M e clinicians and theorists often agree on the importance of working memory to language processing, they are far less unified on the specific processes underlying working memory. I n addition, they disagree about the most valid and reliable methods of evaluation. The objective of this paper is to describe the Competing Language Processing Task, a procedure for estimating children's verbal working-memory capacity. We describe the development and use of the procedure and provide data on the performance of 68 normal school-age children. Clinicians and researchers studying children's language performance and language disorders have various reasons for assessing capacity of working memory. First, according to current models (Baddeley, 1986; Just & Carpenter, 1992), successful comprehension and production of spoken language depend on the continuous integration of linguistic information in working memory. While listening to lectures, responding to questions, or reading, the student must perceive, encode, analyze, compare, and store an ongoing stream of verbal information. The demands on verbal working memory increase -

-

-

-

'This research was supported, in part, by NIDCD Research Grant DC0138-02. We thank Connie Tompkins, Chris DoUaghan, Steve Gaulin, and Gary Holdgrafer for consultation on theoretical and methodological aspects of the work and for commenting on previous drafts. Special thanks are extended to the faculty, staff, and students of the Pittsburgh Public Schools and M e ghen Intermediate Unit who participated in the project. 2 ~ d L e s scorres ondence to Cynthia A. Gaulin, Department of Aud~olo~y and Communication Disorders, chiIdlrenen's Hospital of Pittsburgh, 200 Meyran Avenue, Pitrsburgh, PA 115213.

56

C. A. GAULIN

&

T. F. CAMPBELL

throughout the period of language learning as children encounter longer and more complex sentences and lecture and reading become the dominant modes of learning in school. If some aspects of language processing are inefficient and require additional resources to perform effectively, then total capacity of working memory may be exceeded and language comprehension or production compromised. Second, recent research suggests that verbal working memory is associated with performance on a variety of language tasks. For example, in a series of studies of the relations among working-memory capacity, syntactic processing, and reading abilities, King and Just (1991) found that individual differences in syntactic processing by college students were related to the amount of working memory available for language comprehension processes. They reported that subjects with low capacity showed poorer comprehension of syntactically complex sentences than those subjects with high capacity. These results are consistent with the findings of earlier studies by Daneman and Carpenter (1980, 1983) which showed that differences in working memory predict performance on specific reading comprehension tasks for college students. Finally, differences have been found in phonological memory of normal and language-disordered children. Gathercole and Baddeley (1990) found that language-disordered children exhibited poorer performance when repeating nonsense words and recahng word lists than two control groups who were matched with them on verbal abilities and nonverbal intelligence, respectively. Gathercole and Baddeley proposed that, for these language-disordered subjects, problems with phonological storage in working memory may ". . . play a central role in their disordered language development" (p.

336). Although the current research findings are far from conclusive, available studies do suggest an association between ability to maintain verbal information actively in working memory and performance on various language tasks. Procedures that clarify the relationship between working memory and language performance could have important clinical and research implications. Previous efforts to measure verbal memory have involved verbatim repetition of sentences or lists of digits, letters, or words. These tasks measure static memory capacity and have been shown to be poor predictors of success on tasks which require efficient allocation of limited resources to achieve integrated linguistic processing (Perfetti & Goldman, 1976). King and Just (1991) suggested that this is the case because simple word- or digit-span tasks place limited demands on the resources associated with language comprehension and production. By contrast, the Competing Language Processing Task was developed to estimate verbal memory capacity, taking into account the dynamic nature of working memory in language performance.

CHILDREN'S VERBAL MEMORY, LANGUAGE PROCESSING

Description and Development of the Procedure

The Competing Language Processing Task is based on the experimental listening span test developed by Daneman and Carpenter (1980) to measure verbal memory span of adults. Their test required subjects to listen to groups of 2, 3, 4, 5, and 6 sentences, respond "true" or "false" to each sentence, and then, after each group . of sentences, recall the last word of each sentence in that group. Sentences were 9 to 16 words in length and were reported to be of moderate difficulty. Performance on the listening span test was strongly correlated with reading comprehension and Verbal SAT scores. Because it has been designed for use with children, the Competing Language Processing Task uses shorter and less difficult sentences than those used in Daneman and Carpenter's listening span test. I t requires children semantically analyze and verify the truth of sentences while holding the last word of each sentence in working memory for recall at the end of each group. As in the listening span test, the requirement of a response ensures that sentence comprehension takes place and prevents subjects from concentrating solely on the word-recall task. As illustrated in Table 1, the 42 true and false statements of the task are arranged in two groups at each of six levels of difficulty. The two groups at Level 1 each require comprehension of one statement and recall of only one word. The number of statements in each group increases by one at each level, reaching a total of six statements to be analyzed and six words to be recalled in each of the two groups at Level 6 . Half of the statements presented at each level are true and half are false. However, because at some levels the groups contain an odd number of statements, the number of true and false statements in each group differs. The true and false statements for the task were constructed to control for length and difficulty. Each statement contains three words (subjectverb-object, subject-verb-modifier, or subject-auxiliary-main verb). Simple vocabulary and unambiguous content were used to ensure that the statements could be understood by children as young as 6 years of age. I n addition, an attempt was made to balance processing demands across groups of test statements. To d o this, 25 true statements and 25 false statements were presented individually to six children between the ages of 5 and 12 years (2 boys ages 6-8 and 7-10 yr.; 4 girls ages 5-6, 6-7, 7-5, and 12-6 yr.). The subjects were asked to respond "yes" or "no" to each statement as quickly as they could without making mistakes. Each stimulus sentence was presented by the examiner at a speaking rate of approximately 1.5 words per sec. using live voice. Both the presentation and the subjects' responses were tape recorded using a Sony TCM 5000EV tape recorder. Response latency, which is assumed to be an indicator of increased processing demands (Sternberg,

58

C. A. GAULIN

&

T. F. CAMPBELL

TABLE 1 PRACTICE AND TEST ITEMSFOR COMPETING LANGUAGE PROCESSING TASK Group

Correct Response

Child's Response

Practice Items Children can plav. Apples are black. Ice is hot. Mice eat cheese.

Y N N Y Test Items Level 1 Y

Trees have &. Trains can b.

N

Y Y Y Y

Y Y

Level 2 Pumpkins are purple. Buses have Boys can eat. Bananas are &.

N Y Y N

a.

Carrots can dance. Water is &. Sugar is sweet. . Buckets tell h. Horses have &. Milk is

a.

Feathers can &. Babies drive &. Birds can b. Cars build Snails have &. Chairs eat & c Giants arc 4 Balloons can h.

Level 3 N

N Y N Y Y Level 4 Y

e.

Shoes have ears. Fire burns paper. Robins eat worms. Cars can race. Hotdogs can &. Horses have feet. Dishes can &. Fish pull -. Roses have thorns. Cats can &.

N Y N Y N N

Y Level 5 N

Y Y Y N Y N N Y N

Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y

Y Y Y Y Y Y Y Y Y Y

Level 6 Apples are w. Rabbits read &. Houses can iump.

N N N

Y Y Y

(continued on next page)

Word Recall

CHILDREN'S VERBAL MEMORY, LANGUAGE PROCESSING TABLE 1 (CONT'D) PRAcTlCE

AND

TESTITEMS FORCOMPETING LANGUAGE PROCESSING TASK

Group

2

Correct Res~onse

Child's Response

Word Recall

Pencils eat c h . Airplanes can fl~. Balls are &. Fish can s.lm Clouds wear slll,pers Sheep eat lions People have w. Dogs can run. Lemons are &.

Percentage Correct - TrueIFalse Percentage Correct - Word Recall Score

1969; Meyer, 1970), was measured for each sentence. Using a visual display of the recorded speech segment, C-Speech (Milenkovic, 1988), the interval between the end of the examiner's statement and the onset of phonation of each child's response was measured. The mean response time across the six children for each item and the over-all mean and standard deviation of response times were calculated (over-all M = 822 msec., SD = 428 msec.). I n deciding which sentences would be used in the final version of the procedure, any item with an average response time across subjects of more than 1 standard deviation from the mean was eliminated on the grounds that it was more or less demanding of processing resources than the average for the 50 statements. This eliminated six items (four appeared too demanding and two not demanding enough). Response accuracy across the six subjects was 98% or better for all items included. Two additional statements were eliminated at random to arrive at the 42 statements required to make up two groups of statements at each of six levels. These 42 statements had a mean response time of 741 msec, with a standard deviation of 169 msec. Statements were compiled so that the mean processing time of the statements within any one group did not differ significantly from that of any other group. The test protocol, consisting of these 42 statements, sample items, and instructions, was tape recorded by a female examiner. The instructions were read at 160 wpm. Each test statement required approximately two seconds to present. Each statement was followed by a 3- or 4-second pause during which time the subject was expected to respond "yes" or "no" to the true or false statement. At the end of each group of statements, after another 3or 4-second (M= 3.8) pause, the examiner asked "What was the last word of each sentence?"

Subjects The 68 subjects were drawn from public and private schools in an east-

60

C. A . GAULIN & T. F. CAMPBELL

ern urban center and nearby suburbs. Teachers were asked to identify 6-, 8-, lo-, and 12-yr.-old children from English-speaking homes who were performing within age expectations academically and had no history of neurological deficits, speech or language therapy, psychological treatment, or special services for reading or learning disabilities. Each subject selected (a) was in a regular classroom at an elementary or middle school, (b) scored at or above the 16th percentile on the Peabody Picture Vocabulary Test-Revised (PPVTR) (Dunn & Dunn, 1981), (c) showed a complete phonemic inventory based on imitation of multisyllabic words (adapted from Catts, 1986), and (d) had normal hearing when screened at 25 dB for frequencies 1000, 2000, and 4000 Hz. An attempt was made to test equal numbers of children of each age and gender. Table 2 displays the breakdown of subjects by age, gender, and race and shows the mean PPVT-R score for each group. TABLE 2

Group: Sex/Race

17 Boys 8 Girls 9 Race White 15 Black 2 0 ther Peabody Picture Vocabulary Test-Revised, M 115.53 Ranae 85-145 n

Gender

All

Age Groups, yr.

6

8

10 17

12

19 10 8 9 9 16 12 2 5 1 Standard Score 115.79 120.65 96-143 102-144

Procedure The Competing Language Processing Task was presented to each subject on tape via a Sony tape recorder (TCM 5000EV) through frequency-matched earphones (Sennheiser HD 450). Volume was adjusted to each subject's comfort level before beginning the procedure. The following instructions were given to each subject: I am going to read you some true and false sentences. After each one I want you to say "yes" or "no." After we have done a group of sentences I will ask you to tell me the last word of each sentence in that group. Don't worry about getting them in the right order. As we go on, the groups wd have more sentences. I t will get hard and you won't be able to ask any questions, but I want you to keep on trying to do the best you can. Remember to say "yes" or "no" after each sentence. Then, when I ask you, please say the last word of each sentence you just heard. Do you understand? Let's try some for practice.

The practice items were repeated until the subject understood the task. When necessary, the examiner stopped the tape during the practice items to

CHILDREN'S VERBAL MEMORY, LANGUAGE PROCESSING

61

clarify instructions. Nearly all subjects, including the 6-yr.-olds, were able to perform the task competently after it was demonstrated to them twice.

Other Measures of Verbal Memory To compare performance on the task with performance on other verbal memory tests, measures of digit span and memory for unrelated words were administered. The Auditory Sequences subtest of the Illinois Test of Psycholinguistic Abilities (ITPA) (Kirk, McCarthy, & Kirk, 1968) was chosen as the digit-span task. It was administered and scored as described in the manual, but for a more direct comparison to the present task, the percentage of total items correct rather than t h e scaled score was used in analysis. The Word Sequences subtest of the Detroit Tests of Learning Aptitude-2 (DTLA-2) (Hammill, 1985) was used as the measure of memory for unrelated words. It was administered and scored according to standard procedures described in the manual. Once again, for comparison purposes, the percentage of total items correct was used in the analysis.

Test Sequence The 40-min. battery was administered in the order, Hearing screening, PPVT-R, Competing Language Processing Task, multisyllabic-word irnitation, ITPA Auditory Sequences subtest, and DTLA-2 Word Sequences subtest. Testing took place in a quiet room separated from other school activities and was conducted by one of the authors or by a trained research assistant. Responses were recorded by hand and, for all tests except the PPVT-R, were tape recorded using a second Sony TCM 5000EV tape recorder with a Sony E C M 150T microphone.

Performance on the Competing Language Processing Task Table 3 presents each age group's mean, standard deviation, and range of scores for both the true and false and word-recall components of the task. There were three a priori contrasts of interest in each dataset, including comparisons of 6- and 8-yr.-olds, 8- and 10-yr.-olds, and 10- and 12-yt-olds. Therefore, a Bonferroni-corrected t statistic (Kirk, 1968, p. 79) was used to test for differences in percent of performance across these age levels. For both the true-false and word-recall tasks, a family-wise alpha level of .05 (two-tailed) was selected, yielding a statistical criterion of p < .O2 (two-tailed) for each of the three a priori contrasts. True-False performance.-One component of the Competing Language Processing Task is a semantic-analysis task that requires subjects to respond to true and false statements. As shown in Table 3, the means and standard deviations are similar across the four age levels. All subjects performed with high accuracy. No statistically significant differences obtained between the

C. A. GAULIN & T. F. CAMPBELL TABLE 3

DEVIATIONS, A N D RANGES OF PERCENT CORRECT FORTRUE-FALSE A N D WORD-RECALL TASKS BY AGE

~ ~ A N STANDARD S ,

Aee G r o u ~ vr. .

Measure

True-False Range Word Recall Range

97.76 2.14 92.86-100 50.28 11.35 30.95-73.81

99.25 1.39 95.24-100 60.40 8.70 45.24-80.95

98.74 1.49 95.24-100 71.29 12.10 38.09-85.71

99.21 1.47 95.24-100 73.33 12.08 57.14-95.24

performance of the 6- and 8-yr.-olds (t,, = - 2.44, p = .02), 8- and 10-yr.-olds (t,4= 1.05, p = .31), or 10- and 12-yr.-olds (t,, = - .89, p = .39). Word-recall performance. -The word-recall component of the task required subjects to recall the last word of each true-false statement presented in a given group. This portion of the task provides an estimate of workingmemory capacity for lexical information as well as an indication of the efficiency with which limited processing resources are allocated. Fig. 1 illustrates each age group's performance on the word-recall task. A significant difference was found between 6- and 8-yr.-olds (t,, = - 2.98, p = .006) and between 8- and 10-yr.-olds (t,, = - 3.07, p = ,004). The difference in word recall between 10- and 12-yr.-olds was not significant (t,, = - .47, p = .64). So, ability seems to be age-related to some extent.

RGE GROUP

FIG.1. Means and standard deviations for word-recall task for four

Jge groups, 6, 8, 10,

and 12 yr. old

Correlation With Other Measures Previous studies have shown a relationship between capacity of working memory and language performance (Daneman & Carpenter, 1980, 1983;

63

CHILDREN'S VERBAL MEMORY, LANGUAGE PROCESSING

Gathercole & Baddeley, 1970; King & Just, 1991) but that verbatim repetition tasks do not adequately simulate the demands of language comprehension and production (Perfetti & Goldman, 1776; King & Just, 1971). For this reason, the relationships between performance on the Competing Language Processing Task, PPVT-R, and digit- and word-repetition tests were examined across all age groups using simple bivariate Pearson correlations (Table 4). The correlation between each pair of variables was significant ( p < .01). As anticipated, the strength of the correlation between the receptive vocabulary measure (PPVT-R) and each of the measures of verbatim memory was weak (r = .35 in both cases). The correlations between the two measures of verbatim repetition and the Competing Language Processing Task were moderate ( r = .46 for Digit Span and r = .49 for Word Sequences), but the stronger correlation between the Competing Language Processing Task and the PPVT-R ( r = .63) may hint at a more linguistic basis for the Competing Language Processing Task than for the other two verbal memory tasks. However, these differences were nonsignificant using Hotelling's formula ( p > .05). TABLE 4 BNARUTECORRELATION COEFFICIENTS* FORCOMPETING LANGUAGE PROCESSING TASK (WORDRECALL),DIGITSPAN,WORDSEQLJENCES, AND PPVT-R PERFORMANCE Measure

1

2

3

4

1. Competing Language Processing Task 2. Digit Span

3. Word Sequences 4. Peabody PVT-Revised

DISCUSSION We found that, while true-false judgments remained stable across the ages tested, there was a developmental trend for increased word recall at least through age 10. This suggests that the abihty to carry out such simultaneous processing improves with age at least to a certain point. This improvement may be the result of increased capacity of working memory, more efficient allocation of resources to competing tasks, or both. The question remains whether the competing and difficult processing demands of the Competing Language Processing Task make it a more sensitive predictor of impaired or inconsistent language performance than measures of verbatim repetition. Our results suggest that, for children with normal language skills, a stronger relationship may exist between performance on the Competing Language Processing Task and receptive vocabulary knowledge than between the Competing Language Processing Task and two measures of verbatim repetition. To document this result further, cross-sec-

64

C. A. GAULIN & T. F. CAMPBELL

tional and longitudinal studies should be carried out with normal and language-disordered children to investigate the procedure's relations with known measures of language performance and to verify its sensitivity and specificity in identifying children with or at risk for language-processing difficulties. I n addition, researchers should address whether children with varying capacity of working memory display specific patterns of language performance and to what extent communicative context affects the language processing of such children. At the present time the Competing Language Processing Task, in conjunction with other measures of language and memory, may be a useful tool for identifying and quantifying deficits in verbal working memory that may be associated with inefficient language performance. To this end, the means and standard deviations presented for each of the four age groups provide preliminary guidelines for age-appropriate performance. REFERENCES BADDELEY, A. D. (1986) Working memory. Oxford, UK: Oxford Univer. Press. C ~ r r s H. , (1986) Speech ~~oduction/phonological deficits in reading disordered children. Journal of Learning Disa zhtzes, 19, 504-508. DANEMAN, M., & CARPENTER,I? A. (1980) Individual differences in working memory and reading. Journal of Verbal Learning and Verbal Behavior, 19, 450-466. DANEMAN, M., & CARPENTER, P. A. (1983) Individual differences in integrating information between and within sentences. Journal of Experimental Psychology: Laming, Memory, and Cognition, 9, 561-584. DUNN,L. M., & DUNN,L. M. (1981) Peabody Picture Vocabulnry Test-Revised. Circle Pines, MN: American Guidance Service. GATHERCOLE, S., & BADDELEY, A. D. (1990) Phonological memory deficits in language disordered children. Journal of Memory and Language, 29, 336-360. HAMMILL,D. D. (1985) Detroit Tests o/ Learning Aptitude-2. Austin, T X : Pro-Ed. P. A. (1992) A capacity theory of comprehension: individual difJUST, M. A,, & CARPENTER, ferences in working memory 1'sychological Review, 99, 122-149. KING, J., &JUST,M. A. (1991) Individual differences in syntactic processing: the role of working memory. Journal of Memory and Language, 30, 580-602. K ~ KR., (1968) Experimental design: procedures for the social sciences. Belmont, CA: Brooks/ Cole. KIRK, S. A,, MCCARTHY, J. J., & KIRK, W. D. (1968) Illinois Test of Psycholinguistic Abilities. (Rev. ed.) Urbana, IL: Board of Trustees, Univer. of Illinois. MEYER,D. E. (1970) On the representation and retrieval of stored semantic information. Cognitiue Psychology, 1, 242-300. MILENKOVIC, I? (1988) C-Speech [computer program]. Madison, WI: Univer. of Wisconsin, Electrical and Computer Engineering Department. PERFETTI, C. A,, & GOLDMAN, S. R. (1976) Discourse memory and reading comprehension skill. Journal of Verbal Learning and Verbal Behavior, 14, 33-42. STERNBERG, S. (1969) Memory-scanning: mental processes revealed by reaction-time experiments. American Scientist, 57, 421-457.

Accepted May I G, 1994.