The present study investigates the acquisition of plural markers in German children with and without language impairments using an elicitation task. In the first cross-sectional study, 60 monolingual children between three and six years of age were tested. The results show significant improvements starting at the age of five. Plural forms which require a vowel change (umlaut) but no overt suffix were most challenging for all children. With regard to their error patterns, the typically developing children preferably overapplied the suffix -e to monosyllabic stems and added -s to stems ending in a trochee. Though the children made errors in plural markings, the prosodic structures of pluralized nouns were kept legitimate. In the second study, the production of plural markers in eight children with SLI was compared to age-matched and MLU-matched controls. Children with SLI performed at the level of the MLU-matched controls, showing subtle differences with regard to their error patterns, and their preferences in addition and substitution errors: In contrast to their typically developing peers, children with SLI preferred the frequent suffix -n in their overapplications, suggesting that they strongly rely on frequency-based cues. The findings are discussed from a morphophonological perspective.
The German plural system is a complex inflectional system with a number of idiosyncrasies. A language-learning child has to face a probabilistic system with multiple regularities and subregularities without a clear-cut distinction between regular and irregular forms (see [
The purpose of the present study is to gain an insight into the acquisition of the complex German plural system. By investigating plural formation in children of different ages, we aim at establishing a hierarchy of difficulty of the plural markers and to explore error types and overapplication patterns in more detail. In addition, the intricacies of German plural formation might present a specific obstacle for children with language impairments. Therefore, we examine plural formation in language-impaired children and compare their performance with both age-matched and language-matched peers.
Plural nouns in German are marked by one of the following six suffixes: -n, -en, -e, -s, -er,
Plural forms according to Eisenberg [
Masculine | Neuter | Feminine | |||
(1a) -e (Schwein-e, “pigs”; Buss-e, “buses”) | |||||
(1b) -e + UML (Bäll-e, “balls”) | |||||
(1c) - | (2a) -en (Tür-en, “doors”) | (2b) - | |||
(1c) and (1d) after (pseudosuffixes) | |||||
(3a) -en (Held-en, “heroes”) | (3b) -n (Hase-n, “rabbits”) | (4) -er + UML (Häus-er, “houses”) | (5) -e + UM L (Händ-e, “hands”) | ||
(6) -s (Auto-s, “cars”; LKW-s, “vans”) |
Note that the suffixes -en and -n appear twice in feminine context ((2a) and (2b)) and in masculine contexts ((3a) and (3b), marked forms). The plural form -e plus Umlaut appears in masculine/neuter contexts ((1b), UMLAUT is lexicalized) and in feminine context (
Table
There are different degrees of iconicity inherent in German plural forms. The principle of iconicity states that a morphosemantically marked category, compared to an unmarked category, is expressed preferentially by a longer form [
According to Wiese [
Empirical findings on the acquisition of noun plurals are necessarily language-specific, as they depend on the complexity of the inflectional system of a given language. Since most of the empirical studies have investigated the English plural system so far, no simple generalizations can be drawn for morphologically rich languages. As far as plural acquisition in German is concerned, results seem to depend on the methods used. For example, more errors are produced in elicitation tasks compared to spontaneous speech (cf. [
Studies investigating spontaneous speech indicate an early start of plural marking. Szagun [
Despite the early onset of plural marking, there is a long period of instability, since error rates are relatively high throughout the preschool age (up to 16% according to [
overapplications in typically developing children: spontaneous speech studies.
overapplications in typically developing children: elicitation studies.
The heterogeneous patterns may be due to methodological factors (spontaneous speech versus elicitation tasks), but also certain characteristics of the test items used in elicitation tasks may account for the diverging patterns. In the MacWhinney [
In contrast to unimpaired plural acquisition, the acquisition of noun plurals in German children with Specific Language Impairment (SLI) has not been subject to extensive research. While verb morphology is said to be an area of weakness in SLI, Clahsen [
Two German elicitation studies found differences in error patterns between children with SLI and typically developing children. Schöler and Kany [
In the light of present empirical results on plural acquisition in German, there are still some open questions worth addressing. Basically, findings are inconsistent with respect to the developmental sequence in which plural affixes are mastered and with respect to the question which suffixes are predominantly overapplied. Furthermore, data are sparse concerning plural formation in SLI in comparison to both age-matched and language-matched children. It is still unclear whether children with SLI show a simple delay in their morphological skills or whether they produce particular kinds of errors that are unusual for typical language acquisition. Finally, an aspect that has hardly been addressed so far is the interplay between prosodic and morphological factors in plural formation.
We conducted two studies using the same plural elicitation task. Study 1 investigates the developmental course of plural formation in 60 unimpaired children split over three age groups. Study 2 investigates the performance of children with SLI in comparison to age- and MLU-matched controls. For now, only limited data are available for German comparing performance in plural marking in children with SLI and MLU-matched children, not to mention a comparison of SLI with MLU- and age-matched groups. In both studies, we address the following questions. Overall performance: when do children master the German plural system? Here, improvement with age was expected. However, we did not expect full mastery of the complex plural system even by the age of six. Based on the well-established finding that problems with grammatical morphology are a key characteristic of SLI (see [ Contexts of errors: do children master certain plural forms more easily than others? First, it is assumed that children produce fewer errors with high frequent plural nouns than with low frequent nouns. Second, given the conflicting empirical results concerning the developmental course of plural suffixes in German, we aimed to find evidence for the hierarchy of difficulty in a larger sample of typically developing children. Another question that was addressed was concerned with whether the developmental course of plural forms in children with SLI differs from typical development? Concerning the hierarchy of difficulty of the suffixes, it was assumed that the profiles of children with SLI are similar to those of their language-matched peers. Error types: what kind of errors predominate in children’s incorrect responses? Our objective was to investigate the error types in more detail than in previous studies by calculating the proportion of no markings, substitutions, additions, and partial markings. Do error patterns change with age? Do children with SLI differ with respect to error types from age- and MLU-matched controls? Based on existing results, we expected comparable patterns in SLI- and MLU-matched children. Overapplication patterns: which suffixes are predominantly used in overregularizations? Given the considerable heterogeneity in previous elicitation studies (see Figure Prosodic analysis: as outlined in the introduction, typical plural forms in German are constrained by the prosodic requirement to end in a final trochee. Do children obey or violate this constraint during plural acquisition? Furthermore, it has been suggested that “aspects of prosody may be a problematic area in children with SLI” [
Participants in study 1 were 60 German children between 3 and 6 years of age (see Table
Participants in study 1.
Group | Age | Mean age | Sex | |
---|---|---|---|---|
1 | 20 | 3-4 | 3;4 | 11 girls |
2 | 20 | 4-5 | 4;5 | 7 girls |
3 | 20 | 5-6 | 5;5 | 10 girls |
Eight children with SLI aged from 4;0 to 5;0, and two control groups participated in study 2. The first control group consisted of eight typically developing children of the same age (henceforward referred to as AGE group), and the second was represented by eight younger children (2;8 to 3;5 years) with comparable MLU (henceforward MLU group). All children were monolingual German speakers who lived in Berlin and surrounding areas. Other developmental disorders or hearing impairments were excluded by means of a questionnaire filled out by the parents. For all children, recordings of spontaneous speech were obtained and transcribed in CHAT format. At least 100 utterances of every child were transcribed. MLU in words was determined with the program CLAN (cf. [
Participants in study 2 (age and MLU).
SLI | Age | Sex | MLU | MLU-controls | Age | Sex | MLU | Age-controls | Age | Sex | MLU |
---|---|---|---|---|---|---|---|---|---|---|---|
S-L1 | 4;0 | f | 3.19 | M-A | 2;8 | f | 4.26 | A-M1 | 4;0 | m | 3.90 |
S-J1 | 4;3 | f | 3.19 | M-W | 2;9 | f | 2.86 | A-L1 | 4;0 | f | 3.99 |
S-M | 4;5 | f | 3.77 | M-S | 2;10 | f | 3.50 | A-M2 | 4;2 | m | 4.61 |
S-J2 | 4;6 | f | 3.47 | M-L | 2;10 | f | 3.76 | A-S | 4;2 | f | 3.58 |
S-L2 | 4;7 | f | 3.07 | M-P | 2;11 | f | 3.00 | A-N | 4;2 | f | 4.38 |
S-J3 | 4;9 | f | 2.54 | M-T | 3;1 | m | 3.35 | A-P | 4;7 | f | 3.94 |
S-S | 4;11 | f | 3.16 | M-H | 3;2 | f | 3.32 | A-L2 | 4;11 | f | 4.26 |
S-F | 5;0 | m | 3.64 | M-M | 3;5 | m | 3.40 | A-A | 4;11 | f | 3.41 |
Age-appropriate language development of the control children was assessed by a spontaneous speech analysis and by parental report. The following criteria were used to identify subjects in the SLI group: (a) diagnosed as language impaired by a certified speech-language pathologist, (b) normal hearing and medical history, (c) scoring significantly below age level on a standardized German test of language abilities (
Individual subject profiles: SLI group.
Subjects | |||||||||
Children | Se | Ja | Le | Ju1 | La | Fa | Ju2 | Ma | |
Age | 4;11 | 4;9 | 4;0 | 4;3 | 4;7 | 5;0 | 4;6 | 4;5 | |
MLU | 3.16 | 2.54 | 3.19 | 3.19 | 3.07 | 3.64 | 3.47 | 3.77 | |
Phonemic discrimination | T | 33 | 43 | 13 | 38 | — | — | 0 | 48 |
P | 12 | 31 | 0 | 16 | — | — | 0 | 47 | |
Noun comprehension | T | 51 | 33 | 22 | 51 | 39 | 51 | 39 | 39 |
P | 54 | 7 | 2 | 54 | 17 | 54 | 17 | 17 | |
Verb comprehension | T | 65 | 39 | 26 | 39 | 34 | 36 | 34 | 30 |
P | 99 | 14 | 4 | 14 | 10 | 15 | 10 | 5 | |
Adjective comprehension | T | 51 | 37 | 29 | 22 | 40 | 58 | 40 | 51 |
P | 40 | 15 | 4 | 4 | 17 | 100 | 17 | 40 | |
Comprehension of prepositions | T | 33 | 24 | 24 | 33 | 41 | 59 | 33 | 59 |
P | 14 | 3 | 3 | 14 | 29 | 100 | 14 | 10 | |
Object categorization | T | 57 | 36 | 19 | 38 | 32 | 0 | 19 | 28 |
P | 82 | 6 | 0 | 10 | 3 | 0 | 0 | 0 | |
Noun production | T | 51 | 48 | 38 | 38 | 40 | — | 48 | 43 |
P | 53 | 37 | 8 | 8 | 10 | — | 37 | 17 | |
Verb production | SD | ≤1 SD | ≤1 SD | — | ≤1 SD | ||||
Adjective production | T | 52 | 43 | 19 | 1 | 43 | 52 | 48 | 48 |
P | 61 | 21 | 2 | 1 | 21 | 61 | 33 | 33 | |
Comprehension of wh-questions | T | 45 | 35 | 35 | 24 | 45 | 0 | 29 | 24 |
P | 34 | 8 | 8 | 1 | 34 | 0 | 23 | 1 | |
Production of the definite article | T | 62 | 44 | 44 | 62 | 62 | 46 | 62 | 62 |
P | 100 | 40 | 40 | 100 | 100 | 46 | 100 | 100 | |
Morphology (noun plurals, case marking) | T | 40 | 31 | 28 | 34 | 31 | 36 | 31 | 34 |
P | 20 | 2 | 1 | 6 | 2 | 12 | 2 | 6 |
P: Percentile, T:
Phonological characteristics: SLI group.
Subjects | Substitution of: |
---|---|
Se | /v/, /Ç/, /x/ and reduction of consonant clusters |
Ja | /p/, /v/, /x/, /h/ and reduction of consonant clusters |
Le | /b/, /t/, /f/, /k/, /v/, /z/, / |
Ju1 | /d/, /k/, /g/, /l/, /R/, /f/, /v/, / |
La | /p/, /v/, /j/, /n/, /l/, / |
Fa | Phonetic impairment (/z/, /s/ substituted by / |
Ju2 | /k/, /g/, /Ç/, / |
Ma | /v/, /t/ and reduction of consonant clusters |
There were no significant differences between children with SLI and age-matched controls with respect to age in months (
A plural elicitation task was constructed comprising words covering all German plural forms. The test items were 44 word stimuli reflecting the German plural suffixes. For item selection, we used the classification of plural types, as proposed by Eisenberg (see Table
Examples for plural items: das Schwein— der Hut— das Kissen— der Vater— die Uhr—die Uhr die Feder—die Feder der Prinz— der Affe— das Bild— die Kuh—die K der Teddy—
Frequency of the test items was determined with the help of the German CELEX database ([
The method used was a sentence completion task with pictures. Colored drawings of the stimuli were presented with the single object depicted on the left and multiple objects on the right. The children were asked to produce the plural form (stimulus: “This is one
In order to calculate accuracy, the responses were coded as correct or incorrect. For real words, a response was counted as correct when the appropriate plural marker of the target language was chosen. Phonological errors had no influence on the coding of accuracy as long as the plural marker could be identified. In case of self-corrections, the correct answer was counted. As regards self-corrections that lacked the correct plural form, the last response was taken into account.
Incorrect responses were classified as follows. Addition: the child inadequately adds a plural marker (e.g., Substitution: the correct suffix is substituted by another existing plural suffix (e.g., Incomplete/partial marking: this error type is only possible for items that require umlaut plus suffix. Either umlaut or the plural suffix may be missing (e.g., No marking: the item remains unchanged when a plural marker is required. In this case, the singular form is repeated. No reaction: the child does not answer at all or with “don’t know.” Others: the child responds with another word (e.g.,
No reactions and other responses (error types 5 and 6) were excluded from the analysis, since they are not related to the plural task itself. When classifying the remaining errors, that is, responses that resulted in the production of the target noun, but incorrectly marked for plural, we differentiated between additions, partial markings, and substitutions. Additions and substitutions were subsumed under the category “overgeneralizations” in Laaha et al. [
In some cases two error types had to be assigned to one single item. For example, the correct plural form of
In order to investigate whether prosodic requirements for plural formation in German were considered, we calculated the number of responses that did not end in a final trochee (i.e., monosyllabic forms like *
For study 1, four independent raters classified 20% of the data with respect to error patterns. Interrater agreement was 97.3%. In the same way, four independent raters analyzed the data of four randomly chosen children from the SLI group in study 2. Interrater agreement amounted to 100%.
The data were analyzed for accuracy and error patterns. For the analysis of the error contexts, the percentage of errors in each plural condition was computed. The proportion of error types was determined by calculating the percentage of each error type (no marking, addition, substitution, partial marking) on the total number of errors excluding no and other reactions. For the in-depth analysis of overapplication patterns, the percentage of each suffix on the total number of additions or substitutions was calculated per child.
In study 1, differences between age groups with respect to overall accuracy, the proportion of error types, and suffixes used in overapplications were tested with one-way ANOVAs followed by
Table
Mean number and percentage of correct responses in typical children by age (study 1).
Age | Mean | SD | Minimum | Maximum | Percent correct |
---|---|---|---|---|---|
3;0-4;0 | 31.25 | 5.45 | 19 | 38 | 71.0 |
4;0-5;0 | 32.45 | 4.6 | 22 | 38 | 73.6 |
5;0-6;0 | 37.6 | 1.54 | 34 | 40 | 85.4 |
The children’s overall accuracy in plural production for words increased with age. An overall analysis of accuracy scores over groups (ANOVA) revealed a meaningful difference between groups
With respect to frequency, items with high frequent plural forms were compared to low-frequency forms. Plural markings for words with high frequency were significantly better than, for the low-frequency words (
A detailed descriptive analysis indicates which plural types were most error prone. Figure
Percentage of errors in each plural context in typical children by age (study 1).
As can be seen in Figure
A qualitative analysis of error types focuses on the question how differently error patterns are distributed over age groups. Figure
Error patterns observed in typical children by age (study 1).
An omnibus analysis of variance over the factors error type and age (between-subjects factor) revealed a main effect for error type and age, and an interaction between both factors (see Table
ANOVA over the factor AGE-GROUP ((1) 3-4 years old, (2) 4-5 years old, (3) 5-6 years old) and Error-Type (no markings, addition errors, substitution errors, and partial markings). Post hoc analyses calculated
ANOVA | |
---|---|
Main effect AGE group: | |
Main effect error type: | |
Interaction: | |
Error type | |
No markings | 1 versus 2: |
1 versus 3: | |
2 versus 3: | |
Addition errors | 1 versus 2: |
1 versus 3: | |
2 versus 3: | |
Substitution errors | 1 versus 2: |
1 versus 3: | |
2 versus 3: | |
Partial markings | 1 versus 2: |
1 versus 3: | |
2 versus 3: |
Mean number and percentage of correct responses in typical and language-impaired children (study 2).
Group | Mean | SD | Minimum | Maximum | Percent correct |
---|---|---|---|---|---|
SLI | 20 | 6.05 | 13 | 29 | 45.5 |
MLU | 18.75 | 6.5 | 10 | 28 | 42.6 |
AGE | 31.25 | 3.37 | 26 | 37 | 71.0 |
An in-depth analysis of the incorrect responses revealed which suffixes were used inappropriately. From Figure
Analysis of incorrect responses (in per cent) produced by typical children (study 1).
The next step was to investigate whether the apparent preferences for -s in additions and for -e in substitutions were meaningful and whether there were developmental trends in the overapplication patterns. With respect to additions, an omnibus analysis of variance over the factors suffix (-s and umlaut) and age (between-subjects factor) revealed no main effects for suffix and age, and no interaction. With respect to substitutions, an omnibus analysis of variance over the factors suffix (-e and -(e)n) and age (between-subjects factor) revealed no main effect for age, but a main effect for suffix (
Finally, the proportion of prosodically marked forms (i.e., forms that did not end in a final trochee) in relation to all errors (except for no markings) was calculated. The prosodic constraint was violated in less than 0.4% of all produced plural forms. The rare prosodically marked forms consisted exclusively of monosyllabic stems plus -s instead of bisyllabic plural forms (e.g., *
In general, the number of analyzable stimuli differs between groups: 76.1% in the MLU group, 96.8% in the SLI group, and 96% in the AGE group. The lowest amount of analyzable stimuli in the MLU group results from the fact that the younger children refused to respond in more cases than the older children in the SLI and AGE groups. This may be due to the limited vocabularies of the younger children.
Descriptive statistics for the performance of the three populations tested in study 2 are provided in Table
Next to overall performance, we also investigated the contexts where the errors occurred. All children performed better on high-frequency plurals forms than on items with low frequency (analysed by Wilcoxon-tests). The frequency effect was significant in the SLI group (
In addition, the percentage of errors in each plural context was calculated. Figure
Percentage of errors for each plural context in children with SLI and control groups (study 2).
Again, pure umlauts are more difficult than all other types in all three groups. This prominent difficulty replicates findings observed in Study 1. Figure
Figure
Comparison of the proportion of each error type over the factor group (SLI, MLU, AGE) and pairwise group contrasts (SLI, MLU) and (SLI, AGE) for substitution errors. For pairwise contrasts of the SLI group with each control group,
Error type | Kruskal-Wallis-test | Mann-Whitney |
---|---|---|
No markings | — | |
Addition errors | — | |
Substitution errors | SLI versus MLU: | |
SLI versus AGE: | ||
Partial markings | — |
Error patterns (in per cent) observed in children with SLI and control groups (study 2).
Again, we analyzed which kind of error led to the repetition of the singular form (error type: “no marking”). In the group of the age-matched control children, 55% of no markings occurred in the context of words requiring pure umlaut, that is, the children simply omitted the umlaut. This is a similar proportion as observed in the children of study 1 of the same age (42% in age group 2). However, children with SLI as well as the younger MLU-matched children produced a high proportion of real suffix omissions (e.g., *Gans instead of Gänse, “geese”): only 18% (SLI) and 10% (MLU group) of no markings were due to omission of umlaut.
In a further step, we performed a more fine-grained analysis for addition and substitution errors, in which we focus on the qualitative usage of certain suffixes. The main objective was to find out whether the test groups preferred different suffixes in additions and substitutions. Therefore, the proportion of additions or substitutions involving a certain suffix were calculated on the basis of the total number of addition or substitution errors per child. For additions, Figure
Qualitative comparison of addition and substitution errors. For pairwise contrasts of the SLI group with each control group,
Error type | Kruskal-Wallis-test | Mann-Whitney |
---|---|---|
Addition of -n | SLI versus MLU: | |
SLI versus AGE: | ||
Addition of -s | SLI versus MLU: | |
SLI versus AGE: | ||
Substitution with -e | SLI versus MLU: | |
SLI versus AGE: | ||
Substitution with -(e)n | SLI versus MLU: | |
SLI versus AGE: |
Item list.
Singular form | Plural form | English translation | Frequency group |
hf: high frequency | |||
lf: low frequency | |||
Affe | Affe-n | apes | hf |
Feder | Feder-n | feathers | |
Hase | Hase-n | rabbits | |
Löwe | Löwe-n | lions | |
Rabe | Rabe-n | ravens | |
Schere | Schere-n | scissors | |
Tasche | Tasche-n | bags | |
Zwiebel | Zwiebel-n | onions | lf |
Bär | Bär-en | bears | |
Burg | Burg-en | castles | |
Elefant | Elefant-en | elephants | |
Frau | Frau-en | women | |
Prinz | Prinz-en | princes | lf |
Tür | Tür-en | doors | |
Uhr | Uhr-en | clocks | hf |
Zeh | Zeh-en | toes | |
Brot | Brot-e | breads | |
Fisch | Fisch-e | fishes | hf |
Pilz | Pilz-e | mushrooms | |
Schwein | Schwein-e | pigs | hf |
Baum | Bäum-e | trees | hf |
Fuß | Füß-e | feet | |
Gans | Gäns-e | geese | lf |
Hut | Hüt-e | hats | |
Kuh | Küh-e | cows | lf |
Nuss | Nüss-e | nuts | lf |
Topf | Töpf-e | pots | hf |
Maus | Mäus-e | mice | lf |
Bild | Bild-er | pictures | hf |
Glas | Gläs-er | glasses | hf |
Huhn | Hühn-er | hens | |
Kleid | Kleid-er | dresses | hf |
Lkw | Lkw-s | vans | lf |
Lok | Lok-s | engines | lf |
Teddy | Teddy-s | teddies | lf |
Zebra | Zebra-s | zebras | lf |
Engel | Engel | angels | hf |
Kissen | Kissen | pillows | |
Roller | Roller | scooter | lf |
Messer | Messer | knifes | |
Faden | Fäden | threads | |
Garten | Gärten | gardens | lf |
Vater | Väter | fathers | hf |
Vogel | Vögel | birds | hf |
Incorrect addition (in percent) of plural suffixes in children with SLI and control groups (study 2).
Similar group differences were found for substitutions (Figure
Substitution of plural suffixes in children with SLI and control groups (study 2).
Finally, an analysis of the prosodic structure of the incorrect plural forms revealed that for all groups the proportion of forms not ending in a final trochee was less than 3%. As in the first study, children produced some monosyllabic forms ending in an –s plural, but no form occurred including two adjacent reduced syllables.
The present study examined the acquisition of German noun plurals in typically developing children and children with SLI in an elicitation task. We will now address and discuss the findings in the order of the leading questions outlined in the Section
The general picture that emerges from the data analysis may be characterized as follows: in typically developing children, performance with noun plurals remained on a plateau between age 3;0 to 4;11; afterwards there was a marked improvement. Between 5 and 6 years of age, 80% of the children’s responses were correct, suggesting that full mastery of the German plural system is achieved relatively late in first language acquisition. The observation that complex inflectional systems stabilize relatively late has been shown for other languages as well (e.g., [
As expected, children with SLI clearly fell behind their unimpaired peers in plural marking. Their error rate was significantly higher compared to typically developing children of their own age. Rather, the children with SLI performed at the level of MLU-matched children who were one and a half year younger. Thus, our results do not converge with Clahsen’s suggestion “that the acquisition of German noun plural marking is not impaired in SLI” [
In general, the same effects for frequency were found in all groups of children of different ages, that is an advantage for highly frequent plural forms. Obviously, children are more familiar with high frequent words, which results in a better performance in the plural task. Children with SLI showed a similar advantage for highly frequent words as typically developing children.
Concerning the developmental sequence of the various plural markers, our results mainly converge with findings from other German studies in that -e and -e plus umlaut were mastered early and easily, whereas -s and -er plurals caused more problems. The outstanding mastery of -e in comparison to the other plural suffixes may reflect the fact that this ending is the unmarked way to indicate the function
Previous studies have been equivocal with respect to the suffix -(e)n. In contrast to Laaha et al. [
In some aspects, the developmental course of children with SLI was similar to that of the controls: suffixes that were easily mastered in typically developing children (e.g., -n after schwa) also obtained the highest scores in SLI. The most difficult plural form for unimpaired children, the pure umlaut, was also extremely difficult for children with SLI. So far, our data are in line with Oetting and Rice [
When typically developing children produced errors, different types of errors were observed: substitutions, additions, partial markings, and no markings. The proportion of these error types appeared to be rather stable in typical development except for a decrease of partial markings and a slight increase of “no markings.” Both error types reflect the specific problems in the umlaut condition. Partial markings occurred when a plural form requires a suffix plus the umlaut. In all of these cases the umlaut was omitted. The proportion of “no markings” increased, because the predominant error type of the older children was the omission of the umlaut in pure umlaut plurals.
The error analyses of study 2 revealed that children with SLI applied different types of errors than typically developing children. Children with SLI produced a lower proportion of substitutions, more “no marking” errors and more partial markings than their age-matched peers. This tendency to avoid overt plural marking has been reported in other studies, for example, in Bartke [
The typically developing children’s overapplication patterns in the present study reflects the regularities in the plural system. In line with our hypotheses, -s was mostly used when a suffix was added. Additions mainly occurred in the context of pseudosuffixes (-el, -en, -er, e.g., *
As regards substitutions, typically developing children as expected predominantly used the suffix -e. This finding lends support to elicitation studies on German plural formation (see Figure
Beyond the similarities in the developmental course of plural acquisition, the present data also point to some qualitative differences between typically developing and SLI children with respect to the suffixes used in overapplications. In particular, children with SLI preferred the addition of -(e)n, while both groups of normally developing children mostly added -s. Within their substitutions, children with SLI tended to choose -(e)n more often than both control groups, while unimpaired children preferred -e. This pattern corresponds to the findings of Schöler and Kany [
A tentative interpretation of the differential error patterns in normal and impaired plural acquisition found in our data states that typically developing children show a tendency to meet the prosodic constraint for German noun plurals. In order to produce a trochee with an unstressed final syllable, they choose the most unmarked way by adding a final schwa (-e). Later, they successively acquire the appropriate suffixes of their target language. In contrast, when children with SLI have realized that plural has to be indicated by a suffix, they apply the most frequent one [
Finally, we investigated whether prosodic constraints on plural formation develop with age or are vulnerable in children with SLI leading to more prosodic violations in younger children or in the SLI group. In both studies, it was shown that violations of the prosodic requirement holding for typical German plural forms are very rare. If those forms occur at all, they consist of a monosyllabic stem with a nonsyllabic suffix (e.g.,
In summary, a crucial contribution to the investigation of the developmental course of the German plural system was to tear apart overapplication patterns in addition and substitution errors showing that the prosodic shape of the word stem is a decisive factor for the suffix selection: -s was mainly attached to trochaic forms in zero plurals, whereas -e was applied to monosyllabic stem forms. The diverging findings reported in previous studies may be ascribed to this kind of stem characteristics. The second important finding is that the performance of children with SLI not only emerges at the level of MLU-matched children, but also differs in certain aspects from both control groups. In particular, the overapplication patterns found for a subgroup of children with SLI suggest that plural marking in SLI may be guided by other factors than in typical acquisition of morphological paradigms. A high dependency on suffix frequency may be one explanatory factor.
The present study contributes to existing knowledge about plural acquisition in German. The results show that the acquisition of the plural system takes quite a long time in German as some parts of the system remain difficult due to the underlying morphological complexity and the combination of rule-based and lexicalized learning. Full mastery of the system is not achieved by age 6 yet. An outstanding difficulty emerges with one plural form (pure umlaut) that requires a vowel change within the word but no overt suffix.
Furthermore, this is the first German study that systematically compared abilities of children with SLI with two appropriate control groups (matched for age and MLU). Our findings revealed some similarities between unimpaired and impaired acquisition, as well as some characteristics of impaired plural acquisition. Plural morphology is a domain where the linguistic problems of children with SLI become evident since they were clearly delayed. Given that children with SLI performed at the level of MLU-matched peers, their limitations with plural formation do not represent an outstanding problem, but are in line with their general lag. Moreover, it turned out that children with SLI, like their typically developing peers, were faithful to prosodic constraints on plural production. Beyond the fact that plural formation abilities are not age appropriate in SLI, the results of the present study indicate that children with SLI show specific differences: first, they were more prone to errors on the infrequent suffix -s than typically developing children. Second, they were less inclined to use -s and -e, but more inclined to overapply the frequent suffix -(e)n. These findings point to a higher dependency on input frequency in SLI.
The authors are grateful to Richard Wiese for the helpful comments on the paper. They thank Stefanie Dädelow, Christiane Simon, Juliane Schwartz, and Ina Kruschke for their help with data collection, Julia Siegmüller and Antje Skerra for their assistance during test construction, Conny Nutsch and Anne Weber for assistance with data coding, and Paula Orzechowska for her assistance with the English.