This study employed a paired priming paradigm to ask whether input features influence a child's propensity to use non-nominative versus nominative case in subject position, and to use non-nominative forms even when verbs are marked for agreement. Thirty English-speaking children (ages 2;6 to 3;7) heard sentences with pronouns that had non-contrasting case forms (e.g. Dad hugs it and it hugs Tigger) and it was hypothesized that these forms would lead to more errors (e.g. Himhugs Barney) in an elicited phrase more often than if the children heard contrasting case forms (e.g. Dad hugs us and we hug the doggie). Tense/agreement features were also examined in children's elicited productions. The findings were consistent with predictions, and supported the input ambiguity hypothesis of Pelham (2011). Implications for current accounts of the optional infinitive stage are discussed.

We tested four predictions based on the assumption that optional infinitives can be attributed to properties of the input whereby children inappropriately extract non-finite subject–verb sequences (e.g. the girl run) from larger input utterances (e.g. Does the girl run? Let's watch the girl run). Thirty children with specific language impairment (SLI) and thirty typically developing children heard novel and familiar verbs that appeared exclusively either in utterances containing non-finite subject–verb sequences or in simple sentences with the verb inflected for third person singular -s. Subsequent testing showed strong input effects, especially for the SLI group. The results provide support for input-based factors as significant contributors not only to the optional infinitive period in typical development, but also to the especially protracted optional infinitive period seen in SLI.

Children with specific language impairment (SLI) are distinguishable from typically developing children primarily in the pace and course of their language development. For this reason, they are appropriate candidates for inclusion in any theory of language acquisition. In this paper, the areas of overlap between children with SLI and those developing in typical fashion are discussed, along with how the joint study of these two populations can enhance our understanding of the language development process. In particular, evidence from children with SLI can provide important information concerning the role of language typology in language development, the optimal ages for acquiring particular linguistic details, the robustness of the bilingual advantage for children, the role of input in children's acquisition of grammatical details, the unintended influence of processing demands during language assessment, the contributions of treatment designs to the study of typically developing children, and the study of individual differences in language development.

A group of Finnish-speaking children with specific language impairment (N = 15, M age = 5 years, 2 months [5;2]), a group of same-age typically developing peers (N = 15, M age = 5;2), and a group of younger typically developing children (N = 15, M age = 3;8) were compared in their use of accusative, partitive, and genitive case noun suffixes. The children with specific language impairment were less accurate than both groups of typically developing children in case marking, suggesting that their difficulties with agreement extend to grammatical case. However, these children were also less accurate in making the phonological changes in the stem needed for suffixation. This second type of error suggests that problems in morphophonology may constitute a separate problem in Finnish specific language impairment.

Previous studies of children with language impairment (LI) reveal an insensitivity to aspect that may constitute part of the children's deficit. In this study, we examine aspect as well as tense in Hungarian-speaking children with LI. Twenty-one children with LI, 21 TD children matched for age, and 21 TD children matched for receptive vocabulary scores were tested on their comprehension and production of both imperfective and perfective verb forms in past tense contexts. Although the groups did not differ in their comprehension performance, the children with LI were less accurate than both comparison groups in producing both imperfective and perfective forms. Based on these results, it appears that children with LI have difficulties selecting the appropriate aspectual marking in past tense contexts.

Children with specific language impairment (SLI) vary widely in their ability to use tense/agreement inflections depending on the type of language being acquired, a fact that current accounts of SLI have tried to explain. Finnish provides an important test case for these accounts because: (1) verbs in the first and second person permit null subjects whereas verbs in the third person do not; and (2) tense and agreement inflections are agglutinating and thus one type of inflection can appear without the other. Probes were used to compare the verb inflection use of Finnish-speaking children with SLI, and both age-matched and younger typically developing children. The children with SLI were less accurate, and the pattern of their errors did not match predictions based on current accounts of SLI. It appears that children with SLI have difficulty learning complex verb inflection paradigms apart from any problem specific to tense and agreement.

I commend Johanne Paradis not only for her interesting Keynote Article but also for the careful research that she has conducted along with her collaborators in the area of bilingual language development and disorders. Her contributions have been significant and are sure to shape our theoretical as well as clinical understanding of specific language impairment (SLI). In this Commentary, I focus on three issues. The first stems quite directly from ideas raised in the Keynote Article; the second and third deal with factors that we need to consider when conducting research involving comparison groups of bilingual and monolingual children with SLI.

The aim of this study was to determine whether children with specific language impairment (SLI) are sensitive to completion cues in their comprehension of tense. In two experiments, children with SLI (ages 4 ; 1 to 6 ; 4) and typically developing (TD) children (ages 3 ; 5 to 6 ; 5) participated in a sentence-to-scene matching task adapted from Wagner (2001). Sentences were in either present or past progressive and used telic predicates. Actions were performed twice in succession; the action was either completed or not completed in the first instance. In both experiments, the children with SLI were less accurate than the TD children, showing more difficulty with past than present progressive, regardless of completion cues. The TD children were less accurate with past than present progressive requests only when the past actions were incomplete. These findings suggest that children with SLI may be relatively insensitive to cues pertaining to event completion in past tense contexts.

The acquisition of verb inflections in Tamil, an agglutinating language, was investigated in three 2-year-old children. The findings revealed a high percentage use of verb inflections indicating tense, aspect, modality, person, number and gender by all three children. Explanations for this early, almost error-free acquisition are discussed in terms of the facilitating properties of agglutinating languages.

Young children readily acquire new words with consonants and syllable structures already used accurately (IN words). They have more difficulty acquiring new words with consonants or syllable structures never before produced or attempted (OUT words). In the present study, we examined children's acquisition of a third type of word, containing consonants the children had attempted in the past but never produced accurately (ATTEMPTED words). IN, OUT and ATTEMPTED words and their object referents were presented to 11 young children in a series of play sessions. The children's production and comprehension of the words were then assessed. No comprehension differences among the three types of words were observed. However, ATTEMPTED words as well as OUT words were less likely to be acquired in production than IN words. Some revisions in models of child phonology are proposed to accommodate these findings.

An unusual phonological pattern exhibited by a child aged 2;9 is described. The pattern involved the production of word-final strident continuants in words whose adult forms contain these features in initial, rather than final position (e.g. [ops] for soap). The data are interpreted as compatible with models of child phonology that permit direct mapping of features to final position.

Theories of language learnability have focused on “normal” language development, but there is a group of children, termed “specifically language-impaired,” for whom these theories are also appropriate. These children present an interesting learnability problem because they develop language slowly, the intermediate points in their development differ in certain respects from the usual developmental stages, and they do not always achieve the adult level of language functioning. In this article, specifically language-impaired children are treated as normal learners dealing with an input that is distorted in principled ways. When the children are viewed from this perspective, Pinker's (1984) theory can account for many of the features of their language.