For the purposes of research, we can't deliberately cause brain damage, and so it is difficult to test experimentally. And for patients suffering from brain damage, it can be difficult to tell how much the damage extends beyond the specific area we are studying. There are methods of investigation which can be used though:

• The brain has a mass of 2% of the overall body weight, yet uses 20% of the body's oxygen requirements. This means that blood flow studies can be used: the flow of blood through different parts of the brain may be monitored while a patient uses different linguistic skills


• EEG scans can monitor electrical activity throughout the brain, and can pick up "Event Related Potentials" (ERP)


• electrical stimuli may be applied to parts of the brain to determine the effects on speech, etc.. This is typically done by surgeons operating on the brain who want to make sure they're not chopping out the wrong bit - "Direct Cortical Mapping"


• With dichotic listening, a subject has to listen to different auditory stimuli in each ear, and is asked to respond to one or other. Using this technique, and on the assumption that left-brain is associated with right-ear and vice versa, it has been shown that verbal abilities are associated with the left-brain, and non linguistic (e.g. musical) with the right-brain. Kimura has shown that the "right ear advantage" does not apply to all speech sounds, and mainly affects consonants, particularly short ones. This affect is not confined to speech sounds; the REA appears to apply for brief duration sounds (like the plucking of a guitar string) rather than steady state ones


• With the wada test, an injection of sodium amytal is given which temporarily affects a single hemisphere of the brain, disabling it. In this state, patients' language abilities can be tested.

Experiments on patients who have had the link between the two hemispheres of the brain cut (e.g. for severe epilepsy) seem to show no major change in intellectual capability but do impair skills which require cooperation between hemispheres, e.g. "when an object is presented to the right visual half-field, patients can talk about it...if the same object is presented to the left visual half-field, patients will be unable to talk about it, even though they have seen it: the visual information has gone to the right hemisphere, where no speech processing takes place" (Crystal p261).

Despite language skills being concentrated in the dominant hemisphere, the non-dominant hemisphere also provides language related skills, such as reading logographs, recognising voice intonation and understanding jokes.

Book readings:

• Crystal, ch. 45
• Fromkin: "An Introduction to Language" ch. 2
• Trask: "Language, the Basics", ch. 7