The Development of Naming and Word Fluency: Evidence From ...

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Hebrew-Speaking Children Between. Ages 8 and 17. Gitit Kavé. Department of Communication Disorders. Tel Aviv University, Israel. Naming and word fluency ...

DEVELOPMENTAL NEUROPSYCHOLOGY, 29(3), 493–508 Copyright © 2006, Lawrence Erlbaum Associates, Inc.

The Development of Naming and Word Fluency: Evidence From Hebrew-Speaking Children Between Ages 8 and 17 Gitit Kavé Department of Communication Disorders Tel Aviv University, Israel

Naming and word fluency tests are commonly used in neuropsychological evaluations of both children and adults. The current work examines at which age performance on these tests reaches adult level. One hundred fifty children, 30 in each of 5 age groups (8–9, 10–11, 12–13, 14–15, 16–17), and 30 adults ages 18 to 29, participated in the study. Participants completed a Hebrew naming test, a three-letter phonemic fluency task, and a three-category semantic fluency task (animals, fruits and vegetables, and vehicles). Results show that all measures increase steadily from age 8 to age 17. No difference between the 16- to 17-year-old adolescents and the adults was found on the naming test and on the phonemic fluency task, but such a difference was documented for semantic fluency. The relative contribution of the maturation of vocabulary and the development of efficient retrieval processes to performance on naming and fluency tasks is discussed.

Word retrieval is affected by various neurological conditions in both children and adults and is thus frequently assessed in neuropsychological evaluations with the use of naming and verbal fluency tests (Lezak, 1995). Successful picture naming requires knowledge of the tested vocabulary as well as maturation of retrieval processes. Though children have access to most linguistic constructions before they reach school age, their vocabulary continues to increase as literacy develops (Ravid & Tolchinsky, 2002), and a significant increase in a wide variety of infor-

Correspondence should be addressed to Gitit Kavé, Department of Communication Disorders, Sackler Faculty of Medicine, Tel Aviv University, Sheba Medical Center, Tel Hashomer, Israel, 52621. E-mail: [email protected]

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mation-processing capabilities occurs during the school years (Gillis & Ravid, 1995–2003). While it is reasonable to assume that there is a stage at which an adult level of naming and fluency performance is reached, it is unclear when that stage occurs and whether it occurs at the same time for all measures. The purpose of the current study was to examine these questions. On naming tests, young children make errors because they do not know the appropriate word, the representation of the word is incomplete, and/or they are still in the process of mapping word representations within the lexicon (McGregor, Friedman, Reilly, & Newman, 2002). With only partial knowledge, they cannot choose accurately between the target and other related words, and the vulnerability of newly acquired words to interference leads to retrieval difficulties (Gershkoff-Stowe, 2002). As accessing a word from the lexicon involves the activation and competition of multiple entries, words that are not strong enough are less likely to resist interference than words that are more securely positioned (Gershkoff-Stowe, 2002). Nevertheless, the time course of lexical access and the variables that affect access (e.g., semantic interference and phonological facilitation) are very similar in children, adolescents, and adults (Jerger, Martin, & Damian, 2002). Thus, age leads to an increase in the number of lexical entries, it strengthens existing ones, and it fastens a word’s connections with other entries, but the basic mechanism by which children name pictures resembles the one used by adults. Although naming abilities are present from the very beginning of language acquisition, by the time children enter school they do not reach an adult level on naming tests such as the Boston Naming Test (BNT; Kaplan & Goodglass, 1983), most likely because these tests were originally designed to test adult vocabulary. Using the BNT, Kindlon and Garrison (1984) studied children ages 5;8 to 7;6 and found them to be about 47%1 correct on the 85-item version of the test. Working with Italian children, Riva, Nichelli, and Devoti (2000) found that naming performance on the BNT improved from around 43% at age 5;11 to approximately 72% at age 11;4, not reaching adult level by that age. Similarly, Storms, Saerens, and De Deyn (2004) found an increase in BNT scores from 45% correct at age 6 to 80% correct at age 12 in Dutch-speaking Belgian children, yet there was still a considerable difference between 12-year-old children and adults from the same cultural and language community. Kim and Na (1999) reported that 15- to 19-year-old adolescents did not differ significantly from individuals aged 20 to 44 on the Korean version of the BNT. Therefore, it is reasonable to assume that successful performance on naming tests originally designed for adult speakers will be obtained in adolescence, between age 12 and the end of high school. An investigation of the cues that facilitate children’s successful naming can shed light on whether naming difficulties occurring at ages 8 to 17 result from incomplete vocabulary or from retrieval failure. 1Results are presented here in percentages, unlike in the original publications, in order to allow comparison across studies.

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Like naming, fluency performance is also affected by vocabulary growth and its interaction with the increasing efficiency in word retrieval, but it involves additional cognitive processes. In adults, word generation is most strongly correlated with measures of vocabulary and auditory attention (Ruff, Light, Parker, & Levin, 1997), as well as with articulation speed (Hughes & Bryan, 2002). Fluency performance is tightly connected to executive functioning, and the ability to engage in controlled search is assumed to develop with age, alongside the maturation of the frontal lobes. Research with adults has shown that fluency involves relatively effortful processes of shifting that rely on strategic search and mental flexibility, as well as relatively automatic processes of clustering that rely on word storage (Troyer, 2000; Troyer, Moscovitch, & Winocur, 1997; Troyer, Moscovitch, Winocur, Alexander, & Stuss, 1998). As phonemic fluency develops, the number of switches between word clusters increases, reflecting an improvement in mental flexibility, whereas the development of semantic fluency is more closely associated with an increase in cluster size that reflects the enrichment of semantic knowledge (Sauzéon, Lestage, Raboutet, N’Kaoua, & Claverie, 2004). Studies of children with various neurological disorders provide evidence for the various components of word generation tasks. For example, Cohen, Morgan, Vaughn, Riccio, and Hall (1999) found that the phonemic fluency performance of children with developmental dyslexia, who exhibit deficits in phonological processing, is significantly lower than that of both age-matched normally developing children and children with attention deficit hyperactivity disorder (ADHD). Children with reading disabilities have been found to exhibit lower fluency performance (Brosnan et al., 2002; Korhonen, 1995) for a variety of reasons, including difficulties in phonological awareness, vocabulary development, articulation rate, retrieval, or executive functioning. The executive component in verbal fluency is also documented in studies of pediatric traumatic brain injury (Slomine et al., 2002) and ADHD (Pineda, Ardila, Rosselli, Cadavid, Mancheno, & Mejia, 1998). Moreover, children with frontal lobe epilepsy perform worse on phonemic fluency tasks than children with temporal lobe epilepsy (Hernandez et al., 2002). In normally developing children, performance on fluency measures continues to improve from age 6 to age 12, but it does not reach adult level by that age (Cohen et al., 1999; Klenberg, Korkman, & Lahti-Nuuttila, 2001; Korkman, Kemp, & Kirk, 2001). Korkman et al. suggest that the development of flexible strategy use is particularly protracted, and that unlike performance on other cognitive measures in which asymptote is reached by age 12, verbal fluency tests have no upper limit, and thus no ceiling effect can be detected in childhood. Indeed, Sauzéon et al. (2004) showed increasingly better fluency performance from age 6 through age 16 in French-speaking children, and improvement in performance throughout childhood was seen in Spanish (Matute, Rosseli, Ardila, & Morales, 2004) and English as well (Delis, Kaplan, & Kramer, 2001). Nonetheless, Chan and Poon (1999) noted that while 18-year-old Cantonese-speaking adolescents were significantly better

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than 7-year-old children on semantic fluency, peak performance on this task occurs at ages 19 to 30. Healthy adults tend to provide fewer words by letters than by semantic categories (Kavé, 2005a), and this is also the case in children (Riva et al., 2000; Sauzéon et al., 2004). However, brain pathology can lead to the opposite pattern of performance (e.g., Cerhan et al., 2002), and hence the difference between the two fluency tests is utilized in neuropsychological assessment of specific disorders in the adult population. While age-related changes in semantic fluency are seen early on, the most substantial growth in phonemic fluency does not occur before age 10 (Sauzéon et al., 2004). Nevertheless, within the adult population, some authors have reported less pronounced age differences on the phonemic fluency task than on the semantic task (Gladsjo et al., 1999; Kozora & Cullum, 1995; Mathuranath et al., 2003; Troyer et al., 1997). On the one hand, it is possible that children reach adult level on the easier semantic task first, as it relies on naturally developing categories, whereas grouping words in categories within the phonemic task may depend on later developing literacy skills (Kremin & Dellatolas, 1996). On the other hand, because vocabulary continues to grow, the semantic task may reach an adult level later than the phonemic task, which in turn will reach ceiling as soon as executive functions mature. Alternatively, the determining factor may be the level of ceiling performance, so that the fact that adults generate fewer words on phonemic fluency tasks may make it easier to reach that level in adolescence. The aim of the current study, then, is to examine the effect of age on the development of naming and verbal fluency measures in Hebrew-speaking children. Specifically, the question is not onlywhether these abilities continue to develop from age 8 to age 17, but also whether an adult level is reached in adolescence, and whether it is reached at a similar age for naming, phonemic fluency, and semantic fluency. METHOD Participants One hundred fifty children participated in this study, with 30 children sampled for every two consecutive ages, half male and half female (see Table 1). All children were born in Israel and were native Hebrew speakers. They attended regular schools and had no learning disorders, neurological deficits, or developmental problems, as reported by their teachers or parents. Participants were volunteers with parental consent, recruited either through their school or through word of mouth in various middle-class communities from Bet Shemesh, Ramla, Rosh Ha’ayin, the Tel Aviv area, and a kibbutz in the south. Each community was represented in at least three age groups. In this study, adult performance was determined by testing individuals in the early adult years, from 18 to 29. At age 18, Israeli adolescents graduate from high

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TABLE 1 Sample Characteristics by Age Group Age Group

Grade Levela

n

Number of Females

8–9 10–11 12–13 14–15 16–17 All children 18–29

3–4 5–6 7–8 9–10 11–12

30 30 30 30 30 150 30

15 14 15 15 16 75 17

aBecause children were tested throughout the school year, grade levels are presented for reference only, and the article discusses ages instead.

school and are legally considered adults. Norms on naming and fluency tests for adult Hebrew speakers are available from age 18 on (Kavé, 2005a, 2005b), and various studies have defined adult performance around this age (e.g., Chan & Poon, 1999; Kim & Na, 1999). Thirty adults from this age range who participated in previous population studies of Hebrew naming and fluency (Kavé, 2005a, 2005b) served as a comparison group. These individuals were recruited from the same communities as the children and were selected from the larger population sample if tested on both fluency measures. Like the children, all adults were born in Israel and were native Hebrew speakers. The mean age of this group was 24.5 (SD = 3.6), and the mean education level was 13.9 years (SD = 1.7). Adult participants had no known history of neurological or learning disorders.

Procedure

Naming test. A Hebrew naming test designed to assess naming abilities in adult Hebrew speakers was used (Kavé, 2005b). This test consists of 48 black-and-white line drawings, each referring to a noun that contains a consonant Hebrew root, arranged according to word frequency from very frequent to relatively rare. Standard administration resembles that of the BNT, with two types of predetermined cues (functional and phonemic) that can be offered in case a person fails to name the object in the picture. The functional cue (equivalent to the BNT stimulus cue) defines, whenever possible, what can be done with the object in the picture (e.g., the cue for “key” is “you lock the door with it”). Functional cues avoid the use of the same consonant root that appears in the to-be-named stimulus (i.e., the cue for “key,” maFTeaX, is not PoTXim “open,” because these two words share the same consonantal root). Phonemic cues include the first consonant and vowel of the to-be-named word, the first vowel if a word does not begin with a consonant, or only the first consonant if the word begins with a consonant cluster.

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Each participant was instructed to say in one word the name of the item in the picture. The examiner marked responses as correct or wrote them down in case they differed from the responses specified on the answering sheet. Test items were presented with no time limitation, and participants saw all 48 stimuli even when failing to name several consecutive ones. An erroneous response that was spontaneously corrected before any cue was provided was given full credit. If a general rather than a specific response was provided (e.g., “hat” for “top-hat”), the examiner prompted correct naming by asking, “Is there another word for this picture?” If an item was not spontaneously named or if the participant clearly misperceived the picture, the examiner provided a functional cue. When a response that was very similar to the functional cue was provided (saying “baby’s bed” for “cradle”), or if no correct response was provided following the functional cue, a phonemic cue was offered. Following the standard scoring of the BNT, spontaneous responses as well as responses provided after a functional cue were considered correct responses.

Verbal fluency. In both fluency tests, all responses were recorded verbatim, with repetitions, the same word with a different ending, or perseverations subsequently excluded from the total score. If two homonyms were provided, the second mention was counted only when the participant pointed out the alternate meaning explicitly (i.e., gamal “camel”, “repaid”). Words provided in both masculine and feminine forms (e.g., gever–gvert “mister–mistress”; par–para “bull–cow”) were counted as one, whereas an animal and its offspring were counted as separate words (e.g., para “cow” and egel “calf”). On the semantic test, names of subcategories (e.g., bird) were not given credit if specific items within that subcategory (e.g., dove, eagle) were also provided. When a questionable response was provided, clarifications were invited at the end of the 1-min interval. Slang terms were generally acceptable (e.g., shluk “sip”) as were foreign words (e.g., bandana, gangster). Phonemic fluency was assessed by obtaining the number of words generated in 1 min for the letters bet (/b/), gimel (/g/), and shin (/š/). Instructions were as follows: I want you to say as many Hebrew words as possible that begin with a certain letter. You may say any word except for names of people and places, such as Tomer or Tel Aviv. Also, you should use different words rather than the same word with a different ending. For example, if you say tapuz (“orange”), don’t also say tapuzim (“oranges”). If you say a verb, use the simplest form halax (“he went”) and not halaxti (“I went”) or holex (“he goes”). Please don’t say words that are attached to other words, such as mi-shamayim (“from the sky”) or la-kise (“to the chair”). Semantic fluency was assessed by obtaining the number of words generated in 1 min for each of the following three semantic categories: animals, fruits and vegetables, and vehicles. Fruits and vegetables were treated as one category in order to

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avoid the ambiguity between botanical definitions and common usage (as in “avocado”). It was specified that for the category of vehicles only types of transportation should be provided whereas brand names were unacceptable. Each child was tested individually either at school or at home, and adults were tested either at work or at home. The naming test was administered first and then the two fluency tests, and the order of letters (bet, gimel, shin), as well as the order of semantic categories (animals, fruits and vegetables, and vehicles), was constant across participants.

RESULTS The following analyses were conducted for all three tests: a correlational analysis between age (of children only) and test results in which age was entered as a continuous variable, a t test of gender effects on total scores (of children only), a one-way analysis of variance (ANOVA) with age groups (of children only) as the independent variable and test result as the dependent variable, and pairwise comparisons of consecutive age groups that looked at the adult group as well. Additional comparisons to the adult data and an analysis of the difference in performance between the two fluency measures are also presented. As can be seen in Table 2, total correct naming scores increased steadily with age, and a correlation analysis found a statistically significant high association between these two measures (r = .69, p < .05). Gender had no effect on children’s total naming scores, t(148) = –0.55, p > .05, and therefore all analyses were conducted on data from boys and girls together. A one-way ANOVA with total correct naming score as the dependent variable and age group (8–9, 10–11, 12–13, 14–15, 16–17) as the independent variable revealed a statistically significant effect of age, F(4, 145) = 38.07, p < .05, η2 = 0.512. To compare performance of consecutive age groups, the Bonferroni correction was applied with the .05 alpha level set at .01 for each of the five comparisons. Pairwise comparisons of total naming score showed that the differences between the 8- to 9-year-olds and the 10- to 11-year-olds and between the 14- to 15-year-olds and the 16- to 17-year-olds were statistically significant (statistical analyses are presented in the right-most columns in Table 2). The difference between the 12- to 13-year-olds and the 14- to 15-year-olds and the difference between the 16- to 17-year-olds and the adults were not statistically significant (see Table 2). A closer look at the data revealed that while total correct naming scores of the 16to 17-year-old adolescents resembled adult measures, adolescents provided fewer spontaneous responses and relied more heavily on cues than did the adults. To examine this trend, a repeated-measures two-way ANOVA with cue type as the dependent variable (functional, phonemic) and age group as the independent variable (16- to 17-year-olds, adults) was conducted. This analysis showed a statistically significant

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35.9 41.3 43.9 45.0 46.9 42.6 47.4

M

±5.6 ±4.1 3.8 ±2.9 ±1.2 ±5.4 ±1.1

SD

31.3 36.8 41.4 41.4 44.3 39.0 46.0

M

±5.4 ±4.0 ±4.1 ±3.1 ±2.0 ±5.9 ±2.4

SD

Named Spontaneously

4.5 4.5 2.5 3.6 2.6 3.6 0.9

M ±1.8 ±2.3 ±2.2 ±1.8 ±1.5 ±2.1 ±1.2

SD

Named After a Functional Cue

2.1 2.1 1.0 1.2 0.7 1.4 0.4

M ±1.5 ±1.6 ±1.6 ±1.2 ±0.8 ±1.5 ±0.7

SD

Named After a Phonemic Cue

10.0 4.7 3.1 1.8 0.4 4.0 0.2

M ±5.4 ±3.4 ±3.3 ±2.3 ±0.7 ±4.7 ±0.6

SD

Not Named

4.28 2.57 1.26 3.35 1.56

t(58b)

.000 .013 .212 .001 .124

p

ES 1.10 0.66 0.33 0.85 0.43

Note. ES = effect size; CI for ES = confidence interval for effect size. aItems named spontaneously as well as after a functional cue. bDegrees of freedom for comparing two groups of 30 participants each.

8–9 10–11 12–13 14–15 16–17 All children 18–29

Age

Totala

TABLE 2 Results on Naming Test and Pairwise Comparisons of Total Naming Score

0.54–1.63 0.13–1.17 –0.19–0.83 0.32–1.37 –0.08–0.94

CI for ES

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cue-type effect, F(1, 58) = 36.68, p < .05, η2 = 0.387, as more items were successfully named after functional cues than after phonemic cue in both age groups. Note, though, that phonemic cues were provided only in case functional cues failed to lead to successful naming. The group effect was also statistically significant, F(1, 58) = 22.29, p < .05, η2 = 0.278, as 16- to 17-year-olds required more cues overall than did the adults. In addition, the interaction between cue type and age group was statistically significant, F(1, 58) = 13.94, p < .05, η2 = 0.194, reflecting the fact that the difference between the two age groups was more pronounced on items named after functional cues than on items named after phonemic cues. As can be seen in Table 3, the total number of words provided on the phonemic fluency task increased steadily with age, and a correlation analysis found a statistically significant high association between these two measures (r = .74, p < .05). Gender had no effect on children’s total phonemic fluency scores, t(148) = 1.25, p > .05, and therefore all analyses were conducted on data from boys and girls together. A one-way ANOVA with total phonemic fluency score as the dependent variable and age group (8–9, 10–11, 12–13, 14–15, 16–17) as the independent variable revealed a statistically significant effect of age on the number of words generated on this task, F(4, 145) = 41.67, p < .05, η2 = 0.535. To compare performance of consecutive age groups, the Bonferroni correction was applied with the .05 alpha level set at .01 for each of the five comparisons. Pairwise comparisons of total phonemic fluency score showed that the differences between the youngest group and the 10- to 11-year-olds and between the 10- to 11-year-olds and the 12to 13-years-olds were statistically significant (statistical analyses are presented in the right-most columns in Table 3). The differences between the 12- to 13-year-olds and the 14- to 15-year-olds, between the 14- to 15-year-olds and the 16- to 17-year-olds, as well as between the 16- to 17-year-olds and the adults were not statistically significant (see Table 3). As can be seen in Table 4, the total number of words provided on the semantic fluency task increased steadily with age, and a correlation analysis found a statistically significant high association between these two measures (r = .65, p < .05). Gender had no effect on children’s total semantic fluency scores, t(148) = 0.88, p > .05, and therefore all analyses were conducted on data from boys and girls together. A one-way ANOVA with total semantic fluency score as the dependent variable and age group (8–9, 10–11, 12–13, 14–15, 16–17) as the independent variable revealed a statistically significant effect of age on the number of words generated on this task, F(4, 145) = 28.68, p < .05, η2 = 0.442. In order to compare performance of consecutive age groups, the Bonferroni correction was applied with the .05 alpha level set at .01 for each of the five comparisons. Pairwise comparisons of total semantic fluency score showed that the differences between the youngest group and the 10- to 11-year-olds, as well as between the 16- to 17-year-olds and the adults were statistically significant (statistical analyses are presented in the right-most columns in Table 4). The differences between the 10- to

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5.3 7.4 9.4 11.7 13.5 9.5 13.0

M

±1.8 ±2.1 ±3.4 ±3.8 ±3.9 ±4.3 ±3.6

SD

5.7 7.6 9.8 12.2 13.3 9.7 14.1

M

Gimel

±2.5 ±2.3 ±3.1 ±3.5 ±3.6 ±4.1 ±3.3

SD 6.5 7.2 10.3 11.0 13.8 9.8 15.2

M

Shin

Note. ES = effect size; CI for ES = confidence interval for effect size. aDegrees of freedom for comparing two groups of 30 participants each.

8–9 10–11 12–13 14–15 16–17 All children 18–29

Age

Bet

±2.7 ±2.8 ±3.5 ±3.2 ±4.0 ±4.2 ±4.6

SD 17.5 22.2 29.5 34.9 40.6 28.9 42.3

M

Total

±5.7 ±5.7 ±8.3 ±9.0 ±10.1 ±11.5 ±10.4

SD 3.21 3.96 2.46 2.32 0.65

t(58a)

.002 .000 .017 .024 .522

p

TABLE 3 Results on the Phonemic Fluency Task and Pairwise Comparisons of Total Phonemic Score

0.82 1.03 0.62 0.60 0.17

ES

0.29–1.34 0.47–1.55 0.10–1.13 0.07–1.11 –0.34–0.67

CI for ES

503

11.4 15.2 17.7 18.8 20.9 16.8 23.0

8–9 10–11 12–13 14–15 16–17 All children 18–29

±4.6 ±4.3 ±4.9 ±4.9 ±4.7 ±5.7 ±5.0

SD

8.4 11.8 14.8 16.1 18.7 14.0 22.2

M ±3.0 ±4.4 ±4.2 ±4.3 ±4.1 ±5.4 ±4.4

SD

Fruits and Vegetables

7.3 9.7 11.2 11.3 13.3 10.6 15.1

M ±3.1 ±2.7 ±3.5 ±2.5 ±3.5 ±3.6 ±3.0

SD

Vehicles

Note. ES = effect size; CI for ES = confidence interval for effect size. aDegrees of freedom for comparing two groups of 30 participants each.

M

Age

Animals

27.2 36.7 43.7 46.2 53.0 41.4 60.3

M

SD ±9.2 ±10.2 ±10.4 ±10.0 ±10.3 ±13.3 ±9.4

Total

3.80 2.60 .959 2.58 2.88

t(58a)

.000 .012 .342 .012 .006

p

TABLE 4 Results on the Semantic Fluency Task and Pairwise Comparisons of Total Semantic Score

0.98 0.68 0.25 0.67 0.74

ES

0.43–1.50 0.15–1.19 –0.27–0.75 0.14–1.18 0.21–1.25

CI for ES

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11-year-olds and the 12- to 13-year-olds, between the 12- to 13-year-olds and the 14- to 15-year-olds, and between the 14- to 15-year-olds and the 16- to 17-year-olds were not statistically significant (see Table 4). A difference score was computed for each participant by subtracting the phonemic sum score from the semantic sum score, and percentiles of these differences are presented in Table 5 along with age means and standard deviations. Eleven children (7.3%) and one adult (3%) scored higher on the phonemic fluency test than on the semantic fluency test, thus receiving a negative difference score.

DISCUSSION The present findings show that while some naming and fluency measures reach adult level in adolescence, others do not. As children mature, they are increasingly more capable of naming test items, either spontaneously or following cues, and the number of items that are not named at all decreases steadily until it reaches an adult level at age 16 to 17. Hebrew-speaking adolescents at that age do not differ from adults in the mean total naming score, which includes items named spontaneously and items named after a functional cue. These findings are in line with previous studies of other languages (e.g., Kim & Na, 1999). However, 16- to 17-year-olds name fewer items spontaneously and require more functional cues to arrive at the correct answer than do adults between 18 and 29 years of age. This pattern of results suggests that while the vocabulary necessary for successful completion of the current naming test may not be available to children at age 8, it is acquired by age 16 to 17. Although children could require more cues because they have more trouble identifying the item in the picture for perceptual reasons, Storms et al. (2004) reTABLE 5 Cumulative Percentiles of Fluency Difference Scoresa by Age Group Age Percentile ≤10 11–25 26–50 51–75 76–100 M SD Range

8–9

10–11

12–13

14–15

16–17

18–29

All Children

≤1 2–4 5–8 9–12 13+ 9.7 6.8 –4–23

≤4 5–6 7–11 12–18 19+ 14.5 10.9 –5–48

≤–1 0–5 6–15 16–19 20+ 14.2 10.1 –7–32

≤0 1–3 4–8 9–14 15+ 11.3 10.6 –6–37

≤0 1–3 4–11 12–20 21+ 12.3 11.2 –8–39

≤1 2–11 12–16 17–26 27+ 18.0 10.9 –4–39

≤1 2–4 5–10 11–18 19+ 12.4 10.1 –8–48

aDifference scores were computed for each participant by subtracting the phonemic sum score from the semantic sum score.

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ported that the errors children made on the BNT differed quantitatively but not qualitatively from those made by adults. Other than “don’t know” responses, the most common error type in the Storms et al. study involved semantically related responses, suggesting that word selection, rather than object perception, was at fault. Hence, it is likely that the present results reflect unstable retrieval processes. The literature pertaining to the development of retrieval processes discusses very young children, not adolescents. It has been argued that in early language acquisition, new words are under-represented and are thus more susceptible to interference by related lexical entries (Gershkoff-Stowe, 2002; McGregor et al., 2002). Retrieval difficulties are assumed to arise because lexical entries are incomplete. The greater reliance on cues seen in the present study in children of all ages but especially in the 16- to 17-year-olds, who fail to name only few items, highlights the significant effect that immature retrieval processes has on naming, even toward the end of high school. Apparently, mature naming performance depends not only on the initial acquisition of vocabulary but also on the strengthening of lexical entries and their interconnections. These processes seem to take place over a lengthy period of time. The development of vocabulary and the maturation of retrieval processes contribute to word generation as well. The current study found that while performance on both fluency tasks improves significantly from age 8 to age 17, 16- to 17-year-old adolescents reach adult level only on the phonemic fluency task. This task is tightly associated with the ability to switch from one set to another (Troyer, 2000; Troyer et al., 1997; Troyer et al., 1998), and Sauzéon et al. (2004) maintain that the increase in number of switches between word clusters seen in childhood reflects an improvement in mental flexibility. For that reason, phonemic fluency tasks are commonly used in the assessment of executive functioning in children (Hernandez et al., 2002; Pineda et al., 1998; Slomine et al., 2002). Korkman et al. (2001) have argued that the development of flexible strategy use is a prolonged process that continues past age 12, and the present results show that it reaches maturity during the late teen years. Importantly, it is possible that adolescents reach adult level on this task because ceiling performance is limited and because there is considerable variability among adult participants. Difference scores demonstrate that the majority of children generate fewer words that begin with certain letters than words that belong to specific semantic categories. Clinically, these scores may be useful when assessing certain brain pathologies, as has been suggested in the adult population (e.g., Cerhan et al., 2002), though future studies have yet to examine whether specific childhood deficits lead to a disproportional impairment in one fluency measure relative to the other. The fact that most children provide more words on the semantic task indicates that this task is easier, as has been reported for both healthy adults (e.g., Kavé, 2005a, among others) and children (Matute et al., 2004). While the phonemic task requires grouping of words according to principles that develop along with literacy (Kremin & Dellatolas, 1996), the semantic task is guided by a natural categoriza-

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tion heuristic available to very young children. Indeed, improvement in semantic fluency is seen early on, whereas substantial growth in phonemic fluency occurs only after age 10 (Sauzéon et al., 2004). Nonetheless, in the current study, children of all ages, including 16- to 17-year-old adolescents, provided significantly fewer items by semantic categories than did adults. Sauzéon et al. (2004) ascribed the increase in cluster size seen during the course of the development of semantic fluency to the enrichment of semantic knowledge. Thus, the continual growth of vocabulary may be responsible for the fact that adults generate more words than do teenagers. However, vocabulary continues to expand throughout the adult years as well (e.g. Kemper & Sumner, 2001; Kemper, Thompson, & Marquis, 2001), and yet semantic fluency appears to be negatively affected by aging (Gladsjo et al., 1999; Kozora & Cullum, 1995; Mathuranath et al., 2003; Troyer et al., 1997). Alternatively, greater efficiency in strategy use and the improvement of retrieval processes may account for the significant difference between children and adults on the semantic task (with a decrease in retrieval efficiency accounting for the late life decline on this task). Support for this assumption comes from the current naming findings according to which even when the necessary vocabulary is available, adolescents’ retrieval is less efficient than that of adults, as seen in their greater reliance on cues. Hence, even if children’s vocabulary were comparable to that of adults, children might not be searching the set of exemplars as effectively as adults. Nevertheless, converging evidence from further investigations of retrieval abilities is required for this account to be strengthened. In conclusion, the current research suggests that alongside the maturation of vocabulary, children develop retrieval skills that allow them to use their stored vocabulary more efficiently on various tasks. To date, little research has focused on the development of naming and fluency skills during the teen years, and future work is needed in order to shed more light on the findings reported here regarding this population.

ACKNOWLEDGMENTS Thanks to the participants of this study for volunteering their time and to Naomi Barancik, Yael Leventhal, Amos Raber, Orly Shoshani, and Diana Tsimkin for their help in data collection.

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