Linguistic Development Research Paper (Page 11 of 37) in pdf

4 WHAT IS IT THAT DEVELOPS?

Is it reasonable to assume that evolution has totally decomposed the brain’s language facilities into

tidy subsystems of neural machinery? Given that certain types of focal brain lesion have been

observed to selectively disrupt language - it is not unreasonable. (c.f. anomia though for the other

side to the argument) Lateralisation of the severity of the eﬀect of such lesions points to at least

some localization.

The following working assumption can be used in the analysis of brain-language functionality:

1. The medium of natural language is dominantly and originally acoustic.

2. The anatomic sub-strata for speech function are for the most part concentrated in a particular

region of the left hemisphere.

3. It is possible to recognize in language performance acoustic-phonetic aﬀerent systems as well

as articulatory eﬀectors.

The two poles of the language system are fairly well circumscribed in the cerebral cortex. They

appear to be connected via a ﬁbre tract. That is - there is a set of nerve ﬁbres carrying information

between the two regions. The receptor/aﬀector polarity constitutes a familiar pattern of neural

organization for many functions and is reminiscent of the “reﬂex arc”, which in various forms serves

as the basic building block of the nervous system.

The temptation to draw a parallel between language and other sensori-motor functions should be

resisted. Such a model does not leave room for a description of comprehension or of spontaneous

production of utterances, nor of any of the motivations which we serve by speaking.

While a reﬂex arc can be demonstrated for the speech mechanism as elsewhere in the nervous system,

its function with respect to language appears to be limited to repetition and auditory feedback. There

is little direct coupling between speech production and speech comprehension. This is an important

point since it distinguishes between language as cognitive process and speech as a mechanism of

performance of communication which is coincidentally acoustic/vocal in form.

Can it be assumed that although in some cases there are anatomical territories for language function,

there are such territories for all language functions? It is much easier, for example, to ﬁnd the

anatomical locus for phonological aphasias than for anomia. Anomia is often associated with diﬀuse

cortical disorder such as senile dementia.

Some studies of echolalia indicate that there is a short-term auditory/verbal memory that is separate

from a long-term semantic counterpart. In other studies it has been demonstrated that the lack or

damage of such a short term memory does not hinder comprehension or paraphrasing.

What are the origins of language asymmetry in the brain? Of some of the most elaborate com-

munication systems in the animal kingdom, the majority are organized equally across both brain

hemispheres. There is a small set of animals that do display hemispheric dominance in communi-

cation tasks. For instance, canaries and macaque monkeys. In most cases the songs and calls are

preferentially processed in the left hemisphere rather than the right.

These ﬁndings indicate that the left hemisphere is preferentially disposed towards communication. It

might also be argued that for a computationally intensive tasks such as speech, more eﬃciency would

be gained through processing in just one hemisphere. That would reduce the chance of confusion

between the hemispheres in handling the sensory motor processes that underpin comprehension and

production of language. It could also be argued that if language becomes a major survival advantage,

then it must be protected from accidental damage. If abscesses, strokes or other internal damages

strike with equal probability in either hemisphere, then the chances of a stroke damaging language

are halved by concentrating it in one place. Lack of communication in any member is a blow to the

whole tribe, not just to one individual.

Linguistic Development Research Paper Page 11

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