JSLHR

Research Article

Detection of Lexical and Morphological Anomalies by Children With and Without Language Impairment Monika Pawłowska,a Sarah Robinson,a and Amebu Seddoha

Purpose: The abilities of 5-year-old children with and without language impairment (LI) to detect anomalies involving lexical items and grammatical morphemes in stories were compared. The influence of sentence versus discourse context on lexical anomaly detection rates was explored. Method: The participants were read 3 story scripts and asked to detect the anomalies embedded in them. Results: Typically developing (TD) children outperformed their peers with LI across the board. For both groups, lexical anomalies were easier to detect than morphological anomalies. Similarly, anomalous nouns were easier for both groups to detect compared with anomalous verbs. The latter presented

a particular challenge to the children with LI. Both groups had greater difficulty with lexical anomaly detection in discourse relative to sentence context. Conclusion: These outcomes suggest that children’s ability to detect anomalies is sensitive to the nature of the anomaly and the linguistic context involved in anomaly detection. Future research may address the relative role of linguistic and cognitive factors in anomaly detection.

A

Editor and Associate Editor: Janna Oetting

Data on young children’s ability to detect lexical anomalies in spoken discourse are limited. Skarakis-Doyle (2002) examined the ability of typically developing (TD) children between ages 2;6 (years;months) and 3;11 to detect violations of expectation in familiar stories in which several words had been changed. She found that even the youngest children were able to detect some violations and that detection accuracy increased with age. The children were also more accurate at detecting violations denoting objects than actions and temporal relations. These findings suggest that the ability to detect lexical anomaly in discourse develops fairly early. However, it is unclear whether they were influenced by the children’s familiarity with the stories. Weist, Kaus, and Pantano (1982) investigated the ability of children to detect lexical anomalies in unfamiliar sentences and discourse. They asked TD kindergarten and secondgrade children to listen to short stories and to indicate by raising their hand if they found a word used incorrectly. The anomalous words used were all nouns that were incongruous with either the verb in the same sentence or information provided elsewhere in the story. Results indicated that the children were able to detect more anomalies on the basis of sentential rather than discourse incongruity and that this ability improved with age. Thus, it appears that TD kindergarten children can detect anomalous nouns in unfamiliar discourse and that this

Received July 31, 2012 Revision received January 15, 2013 Accepted June 3, 2013 DOI: 10.1044/1092-4388(2013/12-0241)

Disclosure: The authors have declared that no competing interests existed at the time of publication.

n anomaly or error occurs when a word or a morpheme is incompatible with its surrounding linguistic context. The anomaly may be lexical or morphological in nature. A lexical anomaly involves inappropriate use of a content word (e.g., She drank some book from her cup) that results in semantic incongruity (a book is not a liquid and cannot be drunk). A morphological anomaly involves inappropriate use or omission of a grammatical morpheme (e.g., She are sipping coffee) that results in formal incongruity (lack of number agreement between the subject and the verb). The linguistic context in which an anomaly occurs may be sentence or discourse. An anomalous word or morpheme may be incompatible with local elements or constituents of the sentence, as in the above examples. At the discourse level, it may be incompatible with global linguistic information specified by entities that extend beyond just one sentence (e.g., lexical: She was reading a book. She stopped swimming when she heard a loud noise; morphological: The Tigers played a game last night. They score ten points.).

a

University of North Dakota, Grand Forks

Correspondence to Monika Pawłowska: [email protected]

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Key Words: language, language disorders, children, morphology, specific language impairment

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ability may be sensitive to the different linguistic and cognitive demands of sentence versus discourse processing. Little is known about the ability of preschool children with language impairment (LI) to detect lexical anomalies in discourse. Skarakis-Doyle and Dempsey (2008) studied detection of lexical violations in a familiar story in 10 children with LI ages 3;7 to 5;1. They found that half of the children failed to detect a single anomaly. It is interesting to note that receptive vocabulary and story comprehension scores for these children were comparable to those for younger TD control subjects, suggesting that the root of the difficulty with the experimental task may extend beyond linguistic deficit to include cognitive problems, such as inattention, poor story recall ability, and inability to integrate multiple sources of information. Accordingly, Skarakis-Doyle and Dempsey (2008) proposed that anomaly detection in discourse may depend on a “coalition of skills” related to linguistic knowledge and cognitive functions. Children’s ability to detect morphological anomalies has been studied using grammaticality judgment tasks. In a longitudinal study, Rice, Wexler, and Redmond (1999) found that TD children 5 years and older performed near adult levels on judgment of grammaticality of sentences containing morphosyntactic errors involving tense-agreement markers and progressive –ing. Children between ages 4 and 5 years also demonstrated this skill at levels that were greater than chance. These outcomes are similar to those reported by Cairns, Schlisselberg, Waltzman, and McDaniel (2006), whose stimuli contained 10 types of syntactic errors, two of which were morphological. In this study, 4-, 5-, and 6-year-olds performed differently, and outcomes for the oldest group were close to adult levels. Thus, similar to lexical anomaly detection (Skarakis-Doyle, 2002), these data suggest that sensitivity to morphosyntactic anomalies improves with age in TD preschool children. The ability of children with LI to detect morphological errors has received relatively more research attention compared with investigations of lexical anomaly (Kamhi & Koenig, 1985; Liles, Shulman, & Bartlett, 1977; Lum & Bavin, 2007; Miller, Leonard, & Finneran, 2008; Montgomery & Leonard, 1998; Redmond & Rice, 2001; Rice et al., 1999; SmithLock, 1995; Windsor, 1999). For example, Rice et al. (1999) reported that elementary school-age children with specific language impairment (SLI) detected fewer errors involving verb morphemes than did both age- and mean length of utterance–matched TD peers. Miller et al. (2008) investigated detection of errors involving tense-agreement morphemes, progressive –ing, and possessive –s in 16-year-olds with LI and TD peers. The subjects with LI were further subdivided into those with specific and nonspecific LI on the basis of nonverbal cognition scores above or below –1 standard deviation, respectively. The two groups with LI demonstrated comparable sensitivity to morphological errors, but they both performed below the level of TD peers. Taken together, the findings suggest that poor morphological error detection skills may be associated with LI irrespective of age or cognitive status. Detection of lexical and morphological anomalies relies on familiarity with words, morphemes, and morphosyntactic

structures that underlie primary sentence or discourse comprehension (see Kintsch, 2005). In addition, both the nature of the anomalous item and linguistic context may affect detection rates. Morphological anomaly may be more difficult to detect in comparison to lexical anomaly because the latter is more likely to interfere with the primary task of comprehending the message. Grammatical morphemes tend to make only a peripheral contribution to discourse content, although their misuse can cause problems with message interpretation (e.g., The duck are flying away). Thus, in order to detect morphological anomalies, children need to pay attention to inherently less salient morphosyntactic forms of discourse in addition to constructing meaning. Bialystok (1986) showed that children between ages 5 and 9 years consistently find it difficult to suppress semantic information and focus on morphosyntactic aspects of sentences. Children with LI tend to find this task even more challenging (Lum & Bavin, 2007; Windsor, 1999). Regardless of type, an anomaly may be easier to detect in sentence rather than discourse context. Most studies of morphological error detection in children have used isolated sentences or sentences singled out from stories as stimuli. Sentences embedded in discourse, in contrast, have hardly been used. Consequently, similar to lexical anomaly, detection of morphological error by children at this level of language processing is poorly understood. The goal of the current study was to compare the abilities of 5-year-old children with and without LI to detect lexical and morphological anomalies in novel discourse. It was hypothesized that both groups of children would find it harder to detect errors in discourse compared with sentence context and that outcomes for morphological anomalies would fall below those for lexical anomalies. Anomalous nouns were predicted to be easier to detect than anomalous verbs. Children with LI were expected to perform below the level of their TD peers across the board.

Method Participants Twenty-one TD children and 10 children with LI, whose ages ranged from 57 (4.75 years) to 68 (5.6 years) months (M = 62, SD = 3), participated in the study. Children in both groups were recruited at a Head Start Center in Grand Forks, North Dakota. All participants came from monolingual English-speaking homes as reported by parents. Their language experience was limited to upper Midwestern American English. The TD children and all but two children with LI came from families whose household incomes met the Head Start eligibility criteria, which include annual income at or below 130% of U.S. government poverty guidelines ($28,665 for a family of four in 2010). The study was approved by the University of North Dakota’s institutional review board, and informed consent was obtained from the parents of all children. The TD participants passed a speech, language (agelevel items of the Preschool Language Scale—Fourth Edition; Zimmerman, Steiner, & Pond, 2002), and hearing screening administered by ASHA-certified speech-language pathologists

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(SLPs) and audiologists who were not associated with the study. Participants with LI passed the speech and hearing screening but not the language screening, and they were subsequently diagnosed with language impairment by the Head Start SLPs. Each of them met the criteria for eligibility for special services in the state of North Dakota. These criteria include language deficit in the moderate to severe range. An overall severity rating was calculated from scores based on performance on two standardized language tests (at least one of which was a comprehensive battery), results of informal nonstandardized assessments (language samples, observation checklists), and evaluation of educational impact of language deficits (teacher checklists, curriculum-based assessments). To obtain an independent measure of their language skills, the second author, who is also an ASHA-certified SLP, evaluated all participants on the Clinical Evaluation of Language Fundamentals—Preschool, Second Edition (CELF–P2; Wiig, Secord, & Semel, 2004). The following five language composite scores were calculated from the CELF–P2 subtest scores: Core Language, Content, Structure, Receptive Language, and Expressive Language. The TD group significantly outperformed the LI group on all test components (see Table 1). The mean standard scores of the LI group on the CELF–P2 composites ranged from 77 to 84, with some individual scores of children with LI falling within the normal range. This indicates that for the majority of children with LI, the severity of language impairment as measured by the CELF–P2 was mild to moderate, which differs from the moderate to severe characterization posited by the Head Start SLPs who diagnosed the children. However, it is important to note that the descriptors used by the SLPs were based on a combination of test performance and informal assessments of language use and of the impact of language deficits on classroom performance. In view of lack of agreement in the field on the gold standard for diagnosis, independent clinical diagnosis based on a comprehensive evaluation appears to be a more valid criterion of group membership than performance on a single test (see Dollaghan & Campbell, 1998). Participants were also administered the Brigance Early Childhood Screen—II (Brigance–II; Brigance, 2010) by the Head Start SLPs and teachers. This is a brief developmental screener that evaluates four areas: language, literacy,

mathematics–science, and physical health–development. Raw scores on this test were calculated and compared with criterion scores to determine need for further observation and assessment. Nineteen percent (4/21) of TD children and 40% (4/10) of children with LI failed the screener, but this was judged to be due to lack of exposure to task demands rather than deficient skills. The majority of children were administered the Brigance–II at age 4, approximately 6 months prior to the experimental task. Five TD children and four children with LI were screened at age 3, a year prior to enrollment in the study. Table 2 shows group raw scores for children who were administered the Brigance–II at age 3 and 4. At both age levels, the TD group had a numerically higher mean Brigance–II raw score than the LI group. In the case of 4-year-olds, this difference was significant, t(19) = 2.304, p = .035. Thus, the weaknesses of children in the LI group may have extended beyond language, although this conclusion is limited by the fact that some Brigance–II items did assess language. Subtle weaknesses in areas other than language are common in children with LI and have led some researchers to consider them a secondary aspect of primary LI (see, e.g., Kohnert, Windsor, & Ebert, 2009).

Stimuli Lexical and morphological anomalies were embedded in story scripts that were developed for four commercially available picture books, Going Out (Book A; Davis, 1999), The Apple Pie Tree (Book B; Hall, 1996), Bedtime for Bear (Book C; Becker, 2010), and No David! (Book D; Shannon, 1998). The three scripts had between 65 and 68 utterances (M = 66.3). Mean length of utterance ranged between 6.31 and 6.74 words. In each script, 21 utterances (31.7% of all utterances) contained an anomaly. This means that there was a one-to-three ratio of sentences with and without anomalies. It was anticipated that a higher proportion of sentences containing anomalies might cause the children to focus more on judging correctness of each sentence than on story comprehension, which would detract from a discourse nature of the task. Pilot testing during story development indicated that a one-tothree ratio approximated the typical parent–child storybook interaction while allowing inclusion of a sufficient number of test items for statistical analyses. The book scripts were only

Table 1. Participant characteristics. CELF–P2 composite Age

CL

C

S

RL

EL

Group

n

M

SD

Range

M

SD

Range

M

SD

Range

M

SD

Range

M

SD

Range

M

SD

Range

TD LI

21 10

62 62

3 4

58–67 57–68

105 81

12 8

87–131 75–96

103 82

10 10

85–126 65–96

103 79

13 6

77–129 71–88

103 84

11 7

81–120 71–98

103 77

11 7

79–123 65–89

Note. The larger standard deviations for the TD group reflect the wider range of language abilities represented in this group. All group differences in test scores are significant at the p < .001 level. CELF–P2 = Clinical Evaluation of Language Fundamentals—Preschool, Second Edition; CL = Core Language; C = Content, S = Structure; RL = Receptive Language; EL = Expressive Language; TD = typically developing; LI = language impairment.

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Table 2. Developmental screener (Brigance–II) raw scores. Age 3

Age 4

Group

n

M (SD)

Range

n

M (SD)

Range

TD LI

5 4

80 (6) 57 (23)

75–90 23–71

16 5

70 (16) 58 (7)

34–91 46.5–65

Note. The group difference in mean score of 4-year-olds is significant at the p < .05 level. The participant ages reported here are lower than those reported in Table 1 because the Brigance–II was administered approximately 6 months (4-year-olds) or a year and 6 months (3-yearolds) before the experimental task. The score for one child with LI is not included here because this child was 5 years old when the Brigance–II was administered. Brigance–II = Brigance Early Childhood Screen—II.

loosely related to the text of the original stories. They provided a commentary on the pictures held together by a simple story line. It was important for the story lines and the pictures to be fairly predictable and realistic to make sure that the lexical and the morphological anomalies embedded in the scripts were the only source of incongruity. The pictures were meant to support comprehension, allowing more resources to be devoted to anomaly detection. Shared book reading is an activity that is commonly engaged in by parents and their preschool-age children. It has been successfully used in violation detection tasks in previous research (SkarakisDoyle, 2002; Skarakis-Doyle & Dempsey, 2008). The two types of anomaly, lexical and morphological, were further subdivided into a combined total of seven categories (see Table 3). There were nine tokens of each category (three tokens per script). A sample script with anomalies highlighted is provided in the appendix. Lexical anomaly. The lexical anomalies consisted of open-class words whose meanings were incongruous with the

Table 3. Summary of anomaly types. Anomaly type

Example Lexical

SU Noun SR Noun Verb

She sees the pickles (eggs) in the nest too. They are wearing their pajamas (swimsuits). The little girl is peeling (picking) the apples. Morphological

Omission Plural –s Progressive –ing Auxiliary be Commission Auxiliary be

She is picking many apple(s) for apple pie. The apples are not grow(ing) either. The little girl (is) waiting. He are hiding behind the tree.

Note. Anomalous items are in bold. Items in parentheses are either words originally used in the story that were replaced by an SU or SR noun or verb (lexical anomalies) or grammatical morphemes that were omitted (morphological anomalies). SU = semantically unrelated; SR = semantically related.

linguistic context in which they occurred. They were created by substituting words in the story with semantically related or unrelated items. For example, in one story, children discover a bird’s nest in an apple tree and point to eggs in it. In this context, the following sentence was included: She sees the pickles in the nest too. The word pickles replaced eggs, to which it is not related, as pickles do not belong to the class of objects that are typically found in birds’ nests. This example illustrates a semantically unrelated (SU) lexical anomaly. Later in the same story, the children climb on ladders and pick apples from the tree. In this context, the following sentence was included: The little girl is peeling the apples. The word peeling was used to replace picking, to which it is semantically related as both refer to actions that can be performed on apples. This example illustrates a semantically related (SR) lexical anomaly. All SU lexical anomalies were nouns, whereas SR lexical anomalies were either nouns or verbs. Thus, there were three categories of lexical anomalies: SU nouns, SR nouns, and SR verbs. One factor that may affect the ability to detect lexical anomalies is the frequency with which children hear individual words. Because frequency of exposure appears to be also related to children’s word use (Goodman, Dale, & Li, 2008; Hoff & Naigles, 2002), the latter was examined to determine whether the nouns and the verbs included in the experimental task differed in frequency. The ChildFreq program (Bååth, 2010) was used to search the CHILDES database of spontaneous language samples (MacWhinney, 2000). The mean frequency with which children ages 54 and 66 months used words included in lexical anomalies was calculated. Mean frequency of occurrence per 1,000,000 words for nouns (M = 195, SD = 279) and verbs (M = 283, SD = 226) did not differ significantly, t(24) = –0.782, p = .442. Morphological anomaly. Morphological anomalies consisted of grammatical morphemes that were either missing or misused (overt error), resulting in an ungrammatical sentence. Four categories of morphological anomalies were used depending on the morpheme targeted and the type of error (see Table 3). There were two types of error: omission and commission. Errors of omission involved three different morphemes: noun plural –s (e.g., She is picking many apple[s] for apple pie), progressive –ing (e.g., The apples are not grow[ing] either), and auxiliary be (e.g., The little girl [is] waiting). Errors of commission involved the use of a third-person form of auxiliary be signaling incorrect number agreement (e.g., He are hiding behind the tree). There were two early acquired morphemes (noun plural –s and progressive –ing) and one later acquired morpheme (auxiliary be). Although there is a considerable amount of individual variation (Lahey, Liebergott, Chesnick, Menyuk, & Adams, 1992), the production of all three morphemes is typically mastered by TD children by age 4 (Balason & Dollaghan, 2002; Brown 1973; deVilliers & deVilliers, 1973; Rice, Wexler, & Hershberger, 1998). Five-year-old children with LI produce substantial numbers of the early acquired morphemes but few auxiliaries (Leonard, Bortolini, Caselli, McGregor, & Sabbadini, 1992; Leonard, Eyer, Bedore, & Grela, 1997; Oetting & Rice, 1993; Rice & Oetting, 1993; Rice

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et al., 1998). These trends were reflected in the children’s responses to items on the Word Structure subtest of the CELF–P2 (Wiig et al., 2004). This subtest requires the child to answer a question or complete a sentence by using an appropriate grammatical morpheme. Two test items required the use of progressive –ing (sleeping, walking), and one item each required the use of noun plural (horses) and the third-person singular form of the auxiliary be (He is standing). A review of responses revealed that 86% (18/21) of TD children versus 60% (6/10) of children with LI passed the noun plural, 86% (18/21) of TD children versus 90% (9/10) of children with LI passed the progressive –ing, and 57% (12/21) of TD children versus 10% (1/10) of children with LI passed the auxiliary be test items. Responses to the CELF–P2 items indicated that group differences in the use of the morphemes in question were consistent with those reported in the literature (see Leonard et al., 1997; Rice et al., 1998).

Procedure All participants were administered a vocabulary probe prior to the experiment to determine whether they understood the words used in the task involving detection of lexical anomalies. The probe required the child to select the referent of a stimulus word from an array of three pictures. All children except one had a perfect score on the probe task. One child did not identify one item (computer) possibly because of the appearance of the object in the picture used rather than unfamiliarity with the word involved. This child successfully detected the lexical anomaly when this word was used in the experimental task. All children participated in a group orientation session (three to four children per group) to ensure that they understood the experimental task. They were told that they would listen to a story and that they would need to indicate (by saying “no” or by shaking their heads) when they heard something that sounded “silly” or that they considered to be a mistake. It was also explained to them that a silly item or a mistake could be something that did not make sense or sound right. After some exemplifications, the story was read from Storybook D, and the children identified anomalies contained in it. Positive feedback was provided in the form of praise when an anomaly was spotted (e.g., That’s right! We don’t say “three bird”!). Anomalies that the children had missed were also pointed out then. Each child detected at least one anomaly during the orientation. The orientation and the experiment, including the reading of the story scripts, were conducted by the second author, who is a native speaker of upper Midwestern American English. She monitored her rate of delivery to ensure consistency. As noted above, Storybook D was used in all orientation sessions. Storybooks A, B, and C were used during all experimental sessions, but their order of presentation was counterbalanced across children. In the experimental task, both the lexical and the morphological anomalies were presented concurrently in three stories. The task was administered during an individual testing session that was scheduled approximately a week after

the group orientation and that lasted approximately 20 min. Similar to the instructions given during the orientation, the children were told that three stories would be read to them and that they should indicate whenever they heard something that was silly or a mistake. Two examples of sentences containing lexical and morphological anomalies were given. The three story scripts were read at a natural pace while the subject looked at the pictures in the book and indicated any anomaly detected. Regardless of whether an anomaly was detected, the experimenter continued reading without providing any immediate feedback to reinforce the child’s responses. However, intermittent general praise (e.g., You are a great listener!) was provided. Occasional comments made by the child were also briefly acknowledged to mirror a naturalistic storybook interaction.

Scoring Children’s responses were recorded online by the experimenter and her assistant. Both individuals independently checked off the anomalies detected by the child on their score sheets. Scores were compared directly after each session had been completed. The two scorers agreed on 1,945 out of 1,953 (99.59%) cases. Thus, they disagreed on eight cases. One case was resolved through discussion. The seven remaining cases that were not resolved were excluded from analysis. In addition to keeping track of successful detections of anomalies, the scorers recorded instances when children indicated an anomaly immediately following a sentence where none was present. Four children detected such nonexistent anomalies. They included three TD children and one child with LI. The TD children made 3% (2/58), 15% (2/13), and 16% (5/31) of such errors, and the child with LI made 2% of such errors (1/48). These errors were also excluded from the data. Percent correct anomaly detections across all three storybooks were recorded, and a series of two-way mixed analyses of variance (ANOVAs) were performed on the data.

Results To determine whether anomaly type affected the rate of detection, we conducted an ANOVA with group (TD vs. LI) as between-subjects factor and anomaly type (lexical vs. morphological) as within-subjects factor. Significant main effects were found for group, F(1, 29) = 15.127, p = .001, partial h2 = .343; and anomaly type, F(1, 29) = 98.98, p < .001, partial h2 = .773; with no significant interaction. Both subject groups detected more lexical than morphological anomalies. TD children outperformed their LI peers on both tasks. These results are displayed in Figure 1.

Lexical Anomaly Four SU lexical anomalies that were nouns were incongruous with items specified at the sentence level, and five were incongruous at the discourse level. The nouns incongruous with sentence (M = 154, SD = 145) and discourse context (M = 278, SD = 372) did not differ in frequency, t(7) = –0.625, p = .552. Outcomes for SU noun anomalies in sentence and

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Figure 1. Detection rates for lexical and morphological anomalies.

discourse context were compared across the two groups. Significant main effects were observed for group, F(1, 29) = 10.694, p = .003, partial h2 = .269; and context, F(1, 29) = 12.302, p = .001, partial h2 = .298. There was no significant interaction between group and context, F(1, 29) = 3.412, p = .075, partial h2 = .105. TD children detected more anomalies than did children with LI. For both groups, detection of anomaly was easier at sentence (M = 90%, SD = 20) compared with discourse (M = 78%, SD = 30) level. SR lexical anomalies that were nouns were presented in discourse context only. Performance of the two subject groups on these stimuli was compared with performance on SU nouns presented in discourse context to determine the effect of semantic distance between anomalous nouns and the original nouns they replaced. A significant main effect for group was found, F(1, 29) = 9.766, p = .004, partial h2 =.252. No effect of semantic distance ( p = .622) or interaction ( p = .168) was observed. The children with LI detected fewer SR and SU lexical anomalies that were nouns than did the TD children. Figure 2 displays the results of all comparisons within the category of nouns. To determine whether subjects’ performance was affected by the syntactic category of anomalous word, group detection rates for SR lexical anomalies that were nouns were compared with those that were verbs. The nouns (M = 166, SD = 286) and verbs (M = 283, SD = 226) did not differ in frequency, t(15) = –0.920, p = .372. Two out of nine verbs were incongruous with sentence context, whereas the other seven were incongruous with discourse context. Exclusion or inclusion of the two verbs that were incongruous with sentence context in the data did not affect the results. When all verbs were included in the analysis, ANOVA revealed significant main effects for group, F(1, 29) = 11.074, p = .002, partial h2 =.276; and syntactic category, F(1, 29) = 55.384, p < .001, partial h2 =.656; as well as a significant interaction, F(1, 29) = 7.687, p = .01, partial h2 = .210. The main effects and the interaction are displayed in Figure 3. Anomalous words that were nouns were easier for both groups to detect

Figure 2. Detection rates for lexical anomalies involving nouns.

compared with those that were verbs. The children with LI performed particularly poorly on detection of anomalous verbs.

Morphological Anomaly The rate of detection of morphological anomalies by children with LI (M = 7%, SD = 12) was too low to allow for meaningful comparisons. Consequently, the effect of group membership on the ability to detect the four categories of morphological anomaly (see Table 3) was not analyzed. All subsequent analyses were based on data for TD children only. As is common in storybooks for young children, words, phrases, or syntactic structures were sometimes repeated in adjacent sentences. A sentence containing a morphological

Figure 3. Detection of lexical anomalies involving nouns and verbs.

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anomaly may have been preceded by a sentence containing the relevant morpheme, raising the possibility that priming might have affected anomaly detection. Although the current study was not designed to investigate priming, we examined the stimuli and determined that, in some instances, the stimulus morpheme (noun plural –s, progressive –ing, or auxiliary be) occurred earlier either in the same or preceding sentence (e.g., The mama deer is eating an apple. And the baby deer (is) eating an apple). The numbers of primed versus unprimed instances were three versus six for noun plural –s, two versus seven for progressive –ing, four versus five for auxiliary be omissions, and one versus eight for errors of commission involving auxiliary be. To determine whether priming contributed to morphological anomaly detection, rates for auxiliary be omission with and without prime were compared. This error category was chosen because it had a fairly balanced number of primes versus no primes (see above). A pairedsamples t test showed that the difference between error detection rate for this category in primed (M = 19%, SD = 28) versus unprimed (M = 33%, SD = 35) sentences was not significant, t(20) = –1.936, p = .067, d = .426. Consequently, no distinction was made between primed and unprimed sentences in subsequent analyses. The effect of developmental order on detection of morpheme omissions was investigated using a one-way repeated measures ANOVA with morpheme type (plural –s, progressive –ing, and auxiliary be) as within-subjects factor. A significant main effect was found for morpheme type, F(2, 40) = 15.556, p < .001, partial h2 = .438. Pairwise comparisons with Bonferroni adjustment for multiple comparisons indicated significantly fewer detections of omission of auxiliary be (M = 28%, SD = 28) than of noun plural –s (M = 53%, SD = 36, p < .001) and progressive –ing (M = 46%, SD = 35, p = .003). The difference between detection rates for noun plural –s and progressive –ing omissions was not significant ( p = .473). A paired-samples t test was conducted to compare detection of errors of commission versus omission for auxiliary be. Results indicated that errors of commission (M = 40%, SD = 31) were easier to detect compared with errors of omission (M = 28%, SD = 28), t(20) = 3.557, p = .002. Detection rates for all categories of morphological anomaly are displayed in Figure 4.

Discussion Five-year-old TD children were able to detect a high (80%) percentage of lexical anomalies and a moderate (42%) percentage of morphological errors while listening to novel stories. In contrast, children with LI detected a moderate (52%) and a low (7%) percentage of lexical and morphological anomalies, respectively. These outcomes suggest that the ability to detect lexical anomalies in discourse is well established in TD children by the end of preschool years, whereas morphological error detection skills are still emerging. Development of both skills is delayed in children with LI. The poor performance of children with LI on lexical anomaly detection may have been caused by their lack of

Figure 4. Detection rates for morphological anomalies (TD children only).

understanding of the stimulus words and/or of what they were expected to do in the experiment. The validity of this explanation, however, is questionable in view of the outcomes for the vocabulary probe that preceded the experimental task. In this probe, participants were tested on their knowledge of the words used in lexical anomalies, and all of them earned perfect scores. Similar to this outcome, the individual data indicated that the rates of detection of lexical anomalies for four children with LI were as high as 74% (20/27), 78% (21/27), 74% (20/27), and 88% (24/27). These findings suggest that lack of lexical knowledge or inability to perform the task may not adequately account for the poor performance of the children with LI. One difference between knowledge of isolated words and the ability to detect anomalies involving those words in stories has to do with processing level. Detection of lexical anomaly in stories requires ability not only to access semantic representations of words but also to integrate these representations with the larger linguistic context. The latter ability depends on sentence and discourse comprehension skills. Thus, poor performance of children with LI on lexical anomaly detection may in part be a sign of the weaker comprehension skills of these children relative to TD peers. However, as the extent of linguistic context necessary for anomaly detection increases from sentence to discourse, so does the role of nonlinguistic factors, such as memory and attention, in anomaly detection. Given that subtle weaknesses in nonlinguistic areas are commonly found in children with LI (Kohnert et al., 2009), poor performance of these children on anomaly detection may have both linguistic and nonlinguistic sources. Both subject groups detected anomalies involving SU nouns more frequently in sentence compared with discourse context. Detection of incongruity at sentence level can be accomplished by integrating incoming words with immediately preceding words that have not yet faded from working

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memory (Weist et al., 1982). Such shallow processing may not be sufficient for detection of incongruity at discourse level. The latter requires that the incoming word be integrated with story representation stored in episodic memory. Thus, detection of anomalies at the level of discourse involves deep story comprehension as well as the ability to recall story details. Skarakis-Doyle and Dempsey (2008) suggested that weaknesses in both areas may have contributed to poor performance of children with LI relative to same-age TD peers on a lexical violation detection task involving familiar stories. In the current study, performance of both groups was similarly affected by sentence versus discourse context, suggesting that the greater linguistic and memory demands of discourse context may not have posed a particular challenge to children with LI. However, given the small number of participants, this outcome should be interpreted with caution. In addition, the cognitive effort involved in deep discourse processing may have contributed to the finding of comparable detection rates for anomalies involving SU and SR nouns for both groups. Anomalous nouns were easier to detect than anomalous verbs for both subject groups, with verbs being particularly difficult for children with LI. It is unlikely that word frequency accounts for this finding because the verbs and the nouns used in the lexical anomaly detection task did not differ in frequency. A more likely possibility has to do with conceptual and processing factors. Nouns tend to refer to temporally stable entities, whereas verbs tend to refer to fleeting relations between entities (Black & Chiat, 2003; Gentner, 1978). Accordingly, verb meanings tend to be more conceptually complex and dependent on the surrounding linguistic context compared with noun meanings. Detection of anomalies involving verbs may therefore be more difficult conceptually. It may also involve focusing on a larger linguistic context than detection of anomalies involving nouns. The result of the noun–verb comparison is consistent with a previous report of higher detection rates for violations involving objects compared with actions in younger TD children (Skarakis-Doyle, 2002). The finding that detection of anomalous verbs posed a particular challenge for children with LI is in line with existing evidence of deficits in verb learning and use in these children (Eyer et al., 2002; Rice & Bode, 1993; Watkins, Rice, & Moltz, 1993). The most difficult task for both subject groups was the detection of morphological anomalies. TD children detected only 42% of these anomalies, whereas children with LI detected hardly any. Inadequate knowledge of one or more morphemes and lack of metalinguistic awareness of what constitutes a morphological error may have prevented some of the children from detecting morphological errors. In addition, high linguistic and cognitive demands of discourse comprehension may have made monitoring formal appropriateness in discourse especially challenging. Consistent with this interpretation, TD children in the current study detected a lower proportion of morphological errors than did children of the same age examined by Rice et al. (1999). In the latter study, children judged grammaticality of short sentences singled out from a story. It is thus possible that different performance

of children in the two studies may have been related to different demands involved in sentence versus discourse processing. Perceptual differences may have contributed to the finding that errors of commission involving auxiliary be were detected more readily than errors of omission by the TD children. The former may have been easier to detect because a misused morpheme can provide an overt cue to formal incongruity, whereas any cue provided by the absence of a required morpheme in errors of omission might be weak. Perceptual and processing factors have been linked to morphological error detection in school-age TD children and in adults tested under stressed conditions (McDonald, 2008) as well as adolescents with SLI (Miller et al., 2008). Conversely, differences between detection rates of errors of commission and omission have also been attributed to imperfect linguistic knowledge of rules underlying morpheme use (Rice et al., 1999). The fact that TD children detected more errors of omission involving early (noun plural –s and progressive –ing) compared with a later (auxiliary be) acquired morpheme suggests that differences in linguistic knowledge may have affected detection rates. In summary, the current data indicate that 5-year-olds with and without LI find it easier to detect lexical compared with morphological anomalies. The detection of either type of anomaly may be sensitive to the greater linguistic and cognitive demands involved in discourse compared with sentence processing. Future research needs to include independent measures of comprehension and aspects of cognition, such as memory and attention, in order to tease apart the relative contributions of linguistic and cognitive factors to anomaly detection. Future studies might use tasks assessing grammatical morpheme production and grammaticality judgment in isolated sentences in order to compare different aspects of morpheme processing. The potential influence of priming on morphological error detection also warrants systematic exploration. It is possible that some children may have been so engaged in listening to the story that they were unwilling to interrupt the reading to draw attention to anomalies they may have discovered. Others may have felt uncomfortable to point out errors to the adult experimenter (Walters & Chapman, 2000). These possibilities suggest that the current results may be an underestimation of the actual abilities of the children. The reverse may be the case if the training conducted prior to the experiments enabled the children to pay closer attention and to engage in deeper discourse processing than would normally be possible in spontaneous, untrained situations (Bonitatibus, Godshall, Kelley, Levering, & Lynch, 1988). The current findings have clinical implications related to both assessment and intervention. The results indicate that skills demonstrated at the word or sentence level may have reduced strength at the discourse level of language processing. For this reason, in addition to word and sentence stimuli, discourse tasks need to be included in assessment protocols (Skarakis-Doyle, Dempsey, & Lee, 2008). In addition, consideration of syntactic category and processing level may be important in selecting targets for intervention focusing

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on comprehension monitoring (Dollaghan, 1987; Walters & Chapman, 2000).

Acknowledgments We are grateful to the families and children who participated in the study. We also appreciate the support of the Grand Forks Head Start director, Priscilla Mitchell; the Head Start speechlanguage pathologists, Lori LaHaise and Roxanna Jordheim; and the Head Start teachers. We thank our students Ellie Lindsay and Kristen Hughes and colleagues Alycia Cummings, Manish Rami, and John Madden for their help at various stages of the project. Partial reports of the study were presented at the Symposium on Research in Child Language Disorders (June 2011, Madison, WI) and at the Annual Convention of the American Speech-LanguageHearing Association (November 2011, San Diego, CA).

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Appendix Script for Storybook A, The Apple Pie Tree Anomalies are given in bold, and omitted morphemes are in parentheses. 1. These girls are looking outside at a tree. 2. It is an apple tree. 3. In the winter, the tree doesn’t have any leaves on it. 4. The apples are not grow(ing) either. –ING OMISSION 5. In the spring, the leaves start to grow. 6. The girls is going to look at the tree. AUXILIARY BE COMMISSION 7. A cat is stretching on the tree. 8. He has a blue collar. 9. Here are two bird(s) building a nest. PLURAL –S OMISSION 10. Maybe a baby bird will live in that nest. 11. Look, there are three egg(s) in the nest. PLURAL –S OMISSION 12. The girl is looking up into the nest. 13. She sees the pickles in the nest too. SEMANTICALLY UNRELATED (SU) NOUN 14. The eggs hatched. 15. There are three baby birds. 16. The mommy bird is feeding the babies a grasshopper. SEMANTICALLY RELATED (SR) NOUN 17. The birds have their mouths open. 18. They are hungry little birds. 19. And look at the leaves on the tree. 20. They are grow(ing). –ING OMISSION 21. These tiny flowers are called blossoms. 22. They will grow into apples. 23. The baby birds is growing. AUXILIARY BE COMMISSION 24. Bumble bees are on the tiny flowers. 25. The girls are watching the birds in the tree. 26. And the cat (is) watching the birds in the tree. AUXILIARY BE OMISSION 27. I see a beautiful butterfly too. 28. The wind is blowing. 29. The bears are laughing. SU NOUN 30. The petals are falling off of the flowers. 31. The petals are falling to the ground. 32. The girls are smiling and swimming. SR VERB 33. The birds are flying away. 34. Today it is rain(ing). –ING OMISSION 35. The birds are warm in their nest. 36. They stay safe in the tree. 37. The girls look out of the pumpkin. SU NOUN 38. They are looking at the birds safe in the tree. 39. When the sun comes out, we can see the little baby apples. 40. These little apples will grow and grow. 41. Here is a little worm crawling up the tree. SR NOUN 42. And the birds are flying away. 43. It looks like summer time. 44. The girls are playing in the water. 45. They are wearing their pajamas. SR NOUN 46. The cat looks scared. 47. He are hiding behind the tree. AUXILIARY BE COMMISSION 48. I don’t think he likes the water. 49. The birds are watching. 50. They look like they may want to play too. 51. Now look who is coming to the apple tree. 52. The mama deer is eating an apple. 53. The baby deer (is) eating an apple. AUXILIARY BE OMISSION 54. And a little squirrel wants an apple too. 55. Now the apples are ready. 56. The little girl is peeling the apples. SR VERB 57. She is picking many apple(s) for apple pie. PLURAL –S OMISSION 58. The mom cuts up the apples. 59. She puts them into a pie pan. 60. She sprinkles sugar and cinnamon on top. 61. The little girl (is) waiting. AUXILIARY BE OMISSION 62. She wants to eat the apple pie. 63. Oh, yummy. 64. The pie is done. 65. The girls are drinking the pie. SR VERB 66. I bet it tastes delicious.

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