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Biopsychology. Localisation of aspects of language . Broca’s Area. An area of the left of the frontal lobe called Broca’s area is responsible for the function of speech.
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Biopsychology Localisation of aspects of language
Broca’s Area • An area of the left of the frontal lobe called Broca’s area is responsible for the function of speech. • Damage to this area causes a particular type of language disorder or aphasia. Here, speech is typically slow, laborious and lacking in fluency. However, further research has shown that damage to Broca’s area alone will not cause this type of disorder. The damage has to be the immediately surrounding area also (Naesar et al. 1989)
Wernicke’s area • An area of the left temporal lobe is responsible for speech comprehension, or recognition of spoken words. This is called Wernicke’s area. • Damage to this area causes a different type of disorder. Here, a person has difficulty understanding what another person says, and produces speech which is meaningless.
In contrast to Broca’s aphasia, speech is fluent and without hesitation, but it is ungrammatical and does not make a lot of sense. Notice that Wernicke’s area is part of the auditory cortex, so it is not surprising that hearing what another person is saying is affected. Also notice that both Broca’s and Wernicke’s are located in the left hemisphere. Generally, the left hemisphere is responsible for most aspects of language.
Key StudyPetersen et al. (1988) Aim – To demonstrate different levels of activity in the brain resulting from different types of language. Method– A specialised scanner was used to measure different levels of brain activity in the left hemisphere of the cerebral cortex. Participants were asked, on three separate occasions, to (a) listen passively to a list of nouns on a tape recorder; (b) think of verbs to attach to a noun (e.g. to ‘eat a cake’); and (c) silently read the list of nouns.
Results – The scans showed that different parts of the left hemisphere were active according to the task that the people were engaged with. In (a) Wernicke’s area is activated from listening passively to nouns. In (b) thinking of verbs to attach to a noun activated Broca’s area and other parts of the brain. In (c) Broca’s area is activated by silently repeating nouns. Conclusion– The scan demonstrates that certain areas of the brain are involved with different aspects of language. The brain scans also showed that other areas of the brain were involved, especially when people were asked to link nouns and verbs together.
The functions • The idea that the separate halves of the brain have separate functions is called lateralisation of function or hemispheric specialisation. It is generally regarded : • The left hemisphere is dominant for language; it is also regarded as dominant for logical thought, complex motor behaviour and analytical thought. • The right hemisphere is dominant for non- linguistic, such as the recognition of faces, music and non-logical thought such as emotion and intuition.
Gannon et al. (1998) • Showed lateralisation of function to be the same with macaque monkeys with respect to vocal sounds they make. Cerebral lateralisation has typically been studied using split brain patients. These are people who for some reason have had the corpus callosum surgically cut, hence stopping the communication between the two hemispheres. Sperry (1984) and Gazzaniga (1967) conducted a series of experiments using people with split brains and showed that for visual tasks, each hemisphere does see different things.
Evaluation • Where are thoughts and memories stored in the brain? Those who support the idea of localisation of function try to identify specific areas of the brain for memory. However, others claim that information is stored across the brain as well. • Lashley (1950) conducted research on rats’ brains to try to find specific areas for memory. After 25 years of research, he was not able to find any one area of the rat’s brain that specifically remembered how to run around a maze. • He concluded that learned info is stored in every part of the cortex. This is called Holistic theory of brain function.
Advantages of holism • It is able to explain what is called brain plasticity. People with damage to certain parts of the brain, as a result of a stroke or accident, may recover some or much of the function that has been lost. Recovery may be over months or years. • A head injury may damage a part of the motor cortex so that the person is unable to walk, yet after a period of physiotherapy the ability may be regained.
It seems that while a specific area of the normal brain may have a specific function, another part of the brain may take this over. This may take months or years to happen. Some people do recover some functions, but others do not.
