Bishop,
D. V. (1992). The underlying nature of specific language impairment. The
Journal of Child Psychology and Psychiatry and Allied Disciplines, 33,
3–66.
Hypothesis
1 – Language Impairment as an Output Disorder
According to a
view of SLI as an output disorder, the deficit lies in the ability to transform
a concept in the mind to speech for output. The idea is that articulatory
errors occur with such frequency in these children that this output eventually impairs
the lexical route on which the concept based. However, many children with SLI
do not have a significant articulatory disorder. As a result, this hypothesis
cannot account for SLI.
Hypothesis 2 – Language Impairment as an
Auditory Disorder
In a series of
studies, Tallal and her colleagues provided evidence for auditory deficits in
children with SLI. These children tended to have problems in the perception and
production of rapid sequences of stimuli (Tallal & Piercy, 1973a,b). Several examples of how the auditory
perceptual impairment theory can account for several deficits seen in children
with SLI are provided including phonological problems (e,g., Tallal, & Piercy, 1974), comprehension
difficulties (e.g., Frumkin & Rapin, 1980), and expressive grammatical
problems (Leonard et al., 1987). According to Bishop (1992), further work is
necessary to fully understanding how the auditory limitations theory can
account for different linguistic and non-verbal deficits seen in children with
SLI.
Hypothesis 3 – Linguistic
Interpretations of SLI
The third
hypothesis reviewed by Bishop (1992), addresses the possibility that children with
SLI are born with a deficit in an “innate language acquisition device” that has
been proposed to be responsible for mastering the grammatical relations of a
language. There are many ways in which this language acquisition device may
cause the characteristic impairments that are observed in SLI. One possibility is that children with SLI are
born with the inability to extract the hierarchical structure of their nature
language (Cromer, 1978). Although hierarchical processing deficits have been
reported in children with SLI, the same pattern of performance has also been
observed in other populations such as children who are deaf (Bishop, 1982),
providing contradictory evidence against this theory. An alternative theory is
that children with SLI are impaired in their ability to link grammatical
structure to meaning (Pinker, 1989). This theory has been applied to children
with SLI and their language matched peers, with the finding that children with
SLI have a deficit in what appears to be an innate ability to link grammar to
meaning, while typically developing children do not show the same pattern of
results (Van der Lely, 1990). Although plausible, this finding does not exclude
the possibility that auditory perception issues could be the core deficit in
SLI. Bishops concludes his review by
stating that the current findings are not well understood and that more
sophisticated analyses will need to be conducted before fully rejecting or
accepting this theory.
Hypothesis 4 - Explanation of SLI in
Terms of Piagetian Theory
Bishops fourth
hypothesis explains SLI as being caused by a conceptual deficit. The conceptual
deficit is linked to Piaget’s theory of cognitive development: He saw the
ability to represent something symbolically (e.g.: using a symbol as a stand-in
for an object) as being important for language. Language itself is inherently
symbolic, as we are using words to represent our thoughts, actions, beliefs,
etc. Some researchers have hypothesized that children with SLI are impaired in
their representation of concepts, but the research findings on this are mixed.
Some of the tasks used to assess conceptual development in children require verbal
skills to complete, so children with SLI naturally do poorly on these. Also,
children with SLI seem to do as well as their typically developing peers, it
just takes them longer to do the tasks possibly implicating a speed of
processing deficit and not a conceptual deficit. Overall, it appears that
conceptual development is not impaired in children with SLI, and that their
impairment is due to other factors.
Hypothesis 5- Learning Strategies in SLI
In
the fifth theory discussed in this paper, Bishop posits that the underlying
problem in SLI is a deficit in the rule-learning process. Specifically,
children with SLI may have difficulty testing hypotheses about grammar, a
process that is thought to be necessary in learning language. Research has been
carried out to test how well children with SLI implicitly learn rules in
different kinds of tasks, but results vary depending on the difficulty of the
tasks. In some cases, children with SLI learn the rules as well as typically
developing peers, but have less success in others. Bishop concludes that
children with SLI seem to struggle with rule learning mainly when they are
required to retain the rules for a time.
Hypothesis 6- Limited Information
Processing Capacity as an Explanation for SLI
A limited
information processing capacity model has been proposed as an explanation for
SLI, where children with SLI have been thought to have a reduced capacity for
verbal processing of information. This model has since been altered to account
for a limited information processing system that is not restricted to verbal
processing but also accounts for SLI deficits reported for some visuospatial
and non-verbal information processing tasks as well. One problem with a limited
information processing capacity account of SLI is that the theory is so general
that it can explain almost any pattern of results in terms of capacity of
limitations. Nevertheless, processing capacity in children with SLI remains an
area of continued research interest.
Bloggers for hypotheses 1 through 6, respectively: Alberto Filgueirass, Areej Balilah, Alexandra Smith, Nicolette Noonan, Laura Pauls, & Monica DaSilva
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