Earlier research

2.1  What is the problem – representation or processing?

Much research on SLI has been devoted to finding causal factors. The search has been for either linguistic or perceptual factors to explain the problem – the

PT and children with SLI 67 underlying assumption being that SLI is a syndrome with one single cause. Thus, there are two main perspectives: one characterizes SLI as a representational prob-lem, the other as an auditory processing problem.

Within the first perspective, one early proposal of a domain-specific deficit in the linguistic representation is the feature blindness hypothesis (Gopnik 1994), which assumes that grammatical features such as person and tense are missing from the underlying grammars. Another example is the missing agreement account, according to which children with SLI have problems in establishing agreement relationships, such as using subject-verb agreement markings (Clahsen 1992).

The extended optional infinitive hypothesis (EOI), which is formulated by Rice and Wexler (1996), claims that children with SLI have an extended period where finite-ness is only optionally marked. Typically developing children also have a period of optional infinitives, but it is short-lived and soon disappears. The suggestion is that there is a biologically determined program for optional infinitives and children with SLI have a deficit in this biological program. Each of these three hypotheses refers to problems encountered with the production of verb morphol-ogy in English-speaking children. A fourth proposal for a domain-specific gap in the SLI grammar is that there are problems in establishing hierarchical rela-tionships between linguistic structures. Here, the data come from comprehension experiments that are assumed to reflect internal grammatical representations.

English-speaking children with SLI show difficulties in comprehending structures with dependent relationships (e.g. reflexives and passives). Van der Lely (1998) claims that, at least for a subtype of SLI, the problem is a Representational Deficit for Dependent Relationships (RDDR), which means that the children are unable to link grammatical features.

The second main perspective focusses on auditory processing and suggests that the children’s problems are due to difficulties with the processing of linguistic input.

The surface hypothesis (Leonard 1989, 1998) claims that children with SLI are lim-ited in their auditory processing capacity. They have, for example, difficulties in processing and producing unstressed syllables and morphemes of short duration.

From this perspective, the well-known problem for English-speaking children with SLI in producing 3rd person singular -s is interpreted as a difficulty with the pro-cessing of morphemes of short duration (Leonard 1998). The finding that Italian-speaking children do not exhibit problems with verb inflections seems to be in accordance with this hypothesis, since Italian verb inflections are syllabic and of longer duration than their English counter-parts. The fact that the same English morpheme, the suffix -s, is used by children with SLI as plural marker on nouns but not as person marker on verbs, has been explained by reference to duration and frequency in the input (Hsieh, Leonard, & Swanson 1999). Plural nouns appear in sentence-final position more often than third person singular verb forms, and are

6 Gisela Håkansson

therefore more likely to be of longer duration. Furthermore, frequency in the input may also be beneficial for children with poor auditory processing skills, as plural -s is much more frequent than third singular verb -s in the input to the children, both in caretaker’s speech and in story books (Hsieh et al. 1999).

2.2  Are there specific structures that are likely to be affected?

There are two main reasons behind the intense search for vulnerable structures.

One is the practical goal to find suitable tools for language assessment in differ-ent languages. The other is the existence or non-existence of vulnerable struc-tures, which would have strong implications for the definition of SLI. In Leonard (1998: 66) it is stated that: “The most consistently observed differences between children with SLI and control children have been for finite verb inflections and copula and auxiliary forms requiring agreement”. This finding has influenced much theorizing about SLI and it has spurred a lot of empirical cross-linguistic research targeting verb forms. However, the results are not always the expected ones, but sometimes there are other structures that emerge as critical, as shown in by the quotations about Spanish, Italian and Swedish (1)–(3).

1. Spanish: “As a case in point, extraordinary difficulty with finite verb inflections stands out as a characteristic of SLI in many languages. However, for Spanish, it appears that articles and clitics are at greater risk” (Bedore & Leonard 2005: 223) 2. Italian: “However, relative to MLU controls, Italian-speaking children with SLI do not appear to have special difficulty with most grammatical inflections, in contrast to their extraordinary problem with forms such as articles and clitics”

(Leonard 1998: 96) 3. Swedish: “Our findings on Swedish children with SLI open up the possibility that the especially serious grammatical impairments in children with SLI extend beyond grammatical morphology, contrary to what has earlier been suggested by research on children with SLI” (Hansson & Nettelbladt 1995: 595) In other studies the analyses have not been able to define which structure is the most vulnerable as shown by the quotations on Japanese and French (4)–(5):

4. Japanese: “The results from Japanese did not fit with any of the theoretical accounts of grammatical deficits in SLI”

(Tanaka Welty, Watanabe, & Menn 2002) 5. French: “The results indicate that the spontaneous language of French-speaking children with SLI in the preschool age range is characterized primarily by a generalized language impairment and that morphological deficits do not stand out as an area of particular vulnerability, in contrast with the pattern found in English for this age group.” (Thordardottir & Namazi 2007: 698)

PT and children with SLI 69 In sum, it would appear that for some languages there is enough evidence to claim that there is one particular structure presenting difficulties, for others the SLI problem seems to be more general. This may partly depend on the methodol-ogy used in gathering the evidence, with studies conducted with large groups of children in experimental settings targeting particular structures and overlooking others. The methodology is obviously connected with the theoretical bias.