Comprehension
knowledge is the breadth and
depth of skills and knowledge that are valued by one's culture. Comprehension knowledge includes the ability
to understand spoken language, the breadth of a person's lexicon and general knowledge,
and a person's awareness of grammatical aspects of language.
Is comprehension knowledge an independent
ability or a product of the application of other cognitive abilities? In other words, is it a cognitive ability,
like fluid ability, short term memory and long term storage and retrieval or is
it an area of achievement like reading, writing and math?
As will be discussed below, it's possible
to conceptualize comprehension knowledge both as an ability and as an
achievement.
Language
impairment (LI) is an impairment
in expressive and/or receptive language development in the context of otherwise normal development
(i.e., nonverbal IQ and self-help skills).
Language impairment interferes
with activities of daily living and/or academic achievement. LI
children usually have poor comprehension knowledge, although LI will not always
manifest in poor scores on intelligence subtest scores measuring comprehension
knowledge. The reason for that is that
these tests do not assess all aspects of comprehension knowledge and especially
not the child's command of grammar and syntax.
A broad distinction can be drawn between
two classes of LI model: those that regard the language difficulties as
secondary to more general nonlinguistic deficits, and those that postulate a
specifically linguistic deficit.
The best known example of the first type of
model is the rapid temporal
processing (RTP) theory of Tallal and colleagues, which maintains that
language learning is handicapped because of poor temporal resolution of
perceptual systems. The first
evidence for the RTP theory came from a study where children were required to
match the order of two tones. When tones
were rapid or brief, children with LI had problems in correctly identifying
them, even though they were readily discriminable at slow presentation rates. Children who have poor temporal resolution
will chunk incoming speech in blocks of hundreds of milliseconds rather than
tens of milliseconds, and this will affect speech perception and hence on
aspects of language learning.
In CHC terms Tallal's theory can be conceptualized
as poor auditory processing
and maybe also poor processing speed that
underlie LI.
Another theoretical account that stresses
nonlinguistic temporal processing has been proposed by Miller, who showed that
children with LI had slower
reaction times than
did control children matched on nonverbal IQ on a range of cognitive tasks,
including some, such as mental rotation, that involved no language. Unlike the
RTP theory, this account focuses on slowing of cognition rather than
perception.
A
more specialized theory is the phonological
short-term memory deficit account of LI by Gathercole & Baddeley. These authors noted
that many children with LI are poor at repeating polysyllabic nonwords, a
deficit that has been confirmed in many subsequent studies. This deficit has
been interpreted as indicating a limitation in a phonological short-term memory
system that is important for learning new vocabulary and syntax.
Ullman argues that our use of
language depends upon two capacities: a mental lexicon of memorized words and a
mental grammar of rules that underlie the composition of lexical forms into
predictably structured larger words, phrases, and sentences. On this
view, the memorization and use of at least simple words depends upon an associative
memory (the ability to learn links between pairs
of stimuli, for example between the sequence of phonemes forming a word and its
meaning. Associative memory is a narrow
ability within long term
storage and retrieval). The acquisition and use of grammatical rules depends upon procedural learning and memory (for instance, learning the rule/procedure of past tense
as the addition of "ed" (walk – walked)). Procedural memory enables us to learn many
motor and cognitive "skills" and "habits" (e.g., from
simple motor acts to skilled game playing). LI,
argues Ullman, is caused by poor associative and/or procedural memory. LI is not a specifically linguistic disorder
but is rather the consequence of an impaired system that will also affect
learning of other procedural operations, such as motor skills.
To all
this we can add Cattell's investment theory.
Cattell argued that crystallized knowledge develops through
the investment of fluid
ability. Babies are born with
fluid ability only, which they use in their first encounters and experiences
with the world. Explicit and implicit memories formed in the baby's mind
by these encounters and experiences gradually form his reservoir of
crystallized knowledge. From now on, the baby tackles new experiences
equipped with both fluid ability and crystallized knowledge that he already
acquired. The more knowledge he acquires, the better is his ability to
cope with situations he encounters, and the less fluid these situations become.
The theories presented above enable us to
consider comprehension knowledge as an area of achievement. When a child performs poorly in an area of
achievement (reading decoding, reading comprehension, writing and spelling,
math computations or math reasoning) we look for the cause of his poor
performance among the cognitive abilities (fluid ability, short term memory,
long term storage and retrieval, processing speed, visual processing, auditory
processing, comprehension knowledge). If
comprehension knowledge is also an achievement area, when a child has poor
comprehension knowledge, we should look for the reason for that in one of these
cognitive abilities: fluid ability,
short term memory, long term storage and retrieval, processing speed, auditory
processing and perhaps also visual processing (I don't know a theory linking LI
to poor visual processing).
But comprehension knowledge is different
than other achievement areas. Reading,
writing and math are acquired mostly through formal instruction (there are
aspects of arithmetic that are acquired naturally without instruction – like counting
procedures). Native language is acquired
mostly informally – mostly spontaneously/implicitly. Formal instruction enriches and develops native
language.
The authors above argued that
domain-general deficits in cognitive and perceptual systems are sufficient to
account for LI. This position differs radically from linguistic accounts of LI,
which maintain that humans have evolved specialized language learning
mechanisms and that LI results when these fail to develop on the normal
schedule . A range of theories of this
type for LI focus on the syntactic difficulties that are a core feature of many
children with LI. Children with LI tend to have problems in using verb
inflections that mark tense, so they might say “yesterday I walk to school”
rather than “yesterday I walked to school.” Different linguistic accounts of
the specific nature of such problems all maintain that the deficit is located
in a domain-specific system that handles syntactic operations and is not a
secondary consequence of a more general cognitive processing deficit.
Pennington,
B. F., & Bishop, D. V. (2009). Relations
Among Speech, Language, and Reading Disorders. Annu. Rev.
Psychol, 60,
283-306. http://www.du.edu/psychology/dnrl/Relationsamongspeechlanguageandreadingdisorders.pdf
Schneider,
W. J., & McGrew, K. S. (2012). The Cattell-Horn-Carroll model of
intelligence. Contemporary
intellectual assessment: Theories, tests, and, (3rd), 99-144.
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