Hemispheric Specialisation The cognitive and behavioural functions of the right and left hemispheres The non-verbal vs verbal and analytical functions The findings of research on intact brains

Hemispheric Specialisation This is the idea that one hemisphere has specialised functions, or that it exerts greater control over a particular function. It is also known as hemispheric dominance and hemispheric lateralisation. Both the left and right hemispheres are involved in nearly all functions.

LEFT HEMISPHERE SPECIALISATIONS The left hemisphere specialises in verbal and analytical functions. Verbal functions involve the use or recognition of words eg. reading, writing, speaking and understanding speech. Analytical functions involve breaking down a task into its key parts and approaching it in a sequential, ‘step by step’ way, as is required when using logical reasoning to interpret and apply a formula to solve a maths problem.

RIGHT HEMISPHERE SPECIALISATIONS The right hemisphere specialises in non-verbal functions that are not dependent on language skills eg. Spatial and visual thinking such as completing a jigsaw puzzle, reading a map, recognising faces and tunes; appreciating music and artworks; creativity; and fantasy eg daydreaming.

LEFT HEMISPHERE Focus is on small details, zooms in on specifics and is local. Processes information logically, sequentially and analytically. Receives sensations from the right side of the body. Motor functions include: Controls voluntary bodily movements on the right side of the body and the production of speech. Perceptual functions include: Comprehension of language Cognitive functions: Reading, writing, analytical thinking, sequential processing, logical reasoning and mathematics. RIGHT HEMISPHERE Focus is on a wide-angle view, assembling pieces of the world into a coherent picture and is global. Processes information intuitively (ie. less logically) and holistically (whole patterns simultaneously). Receives sensations from the left side of the body Motor functions include: Controls voluntary bodily movements on the left side of the body. Perceptual functions include: Recognition of faces and patterns. Cognitive functions: Musical ability, spatial ability-design, movement, dance, emotional expression and detection of emotion.

Left versus right

Is it as simple as this?

Another way of looking at it…

RESEARCH ON HEMISPHERIC SPECIALISATION There are 3 main approaches to conducting research on hemispheric specialisation. They are: 1. Studying people with brain damage 2. Studying people who have had a split-brain operation 3. Studying people with intact, undamaged brains.

BRAIN DAMAGE RESEARCH ●Injuries, stroke or lesions reveal: Left hemisphere damage is associated with language disorders (eg aphasias) Right hemisphere damage is associated with visual-spatial disorders(eg. difficulty recognising faces) called facial agnosia or prosopagnosia, also neglect syndrome and spatial disorientation. Damage to the Broca’s area in the frontal lobe of the left cerebral hemisphere is associated with the production of fluent speech. It produces speech that is very deliberate, consisting of a few words with very simple grammatical structure, such as “Mother went shop” instead of “My mother went to the shop”. The damage rarely results in the total loss of speech. Damage to Wernicke’s area in the temporal lobe of the left hemisphere results in people producing meaningless speech that is not considered to be understandable language.

Neglect Syndrome: A disorder caused by damage to the right hemisphere Someone with this disorder behaves as if the LEFT side of their world does not exist. For instance, if asked to copy a picture of a house they will only draw the right side of it.

SPLIT BRAIN OPERATIONS  Patients who have undergone a procedure called a split-brain operation have their corpus callosum surgically cut, which is a bundle of nerve fibres that connect the two hemispheres thereby disconnecting one hemisphere from the other.  This procedure was first used in the 1940’s to stop recurring seizures in severe cases of epilepsy.  In the 1960’s Roger Sperry conducted a series of tests on split-brain patients which involved the participants viewing visual information being presented to only one hemisphere.  Information presented to the left visual field only (to the left side of patients vision) was sent to the right hemisphere of the brain and information presented to the right visual field only was sent to the left hemisphere.

Sperry’s split-brain research Split brain studies reveal: 1. Ability to verbally name and identify words and objects flashed to the left hemisphere. 2. Inability to verbalise words or name objects visually flashed to the right hemisphere; patients can identify these objects by touch alone using their left hand (ie. Controlled by the right hemisphere) 3. Spatial puzzles are solved better using the left hand.

Sperry’s split-brain research cont… When Sperry flashed objects in the left visual field (and these were sent to the right hemisphere) his patient only known as N.G. could not say what she saw (because the area of the brain responsible for speech is in the left hemisphere). To check that she did actually see an object when presented in the left visual field Sperry asked N.G. to use her left hand to reach under the partition for the object. N.G. could correctly do this because her left hand was controlled by the right hemisphere that also saw the image of the object. The message from the primary motor cortex in the right hemisphere for the left hand to move does not use the corpus callosum.

Research findings on intact brains Research in this area has concentrated on two sensory systems- vision and hearing. Psychologist’s can easily measure participants’ responses using these senses A tachistoscope is a type of projector that can be used to present visual information to each visual field and therefore each hemisphere independently. A participant fixates on a centre point marked by a dot or a cross. When non-verbal information is presented to the right hemisphere (and projected to the participants left visual field) it is recognised faster than when presented to the left hemisphere (projected to participants right visual field) since processing of non-verbal information is dominated by the right hemisphere.

Research findings on intact brains… cont People recognise verbal information faster when these are presented to the left hemisphere than when they are presented to the right hemisphere. That is, people identify verbal stimuli, words more quickly when flashed to the right visual field only. Evidence for hemispheric specialisation is provided by brain imaging techniques that capture images of activity during certain types of tasks. Recordings of the neural activity in the brain on people with intact brains reveal that there is greater brain wave (EEG) activity in the left hemisphere with verbal tasks and greater activity in the right hemisphere with spatial tasks. Psychologists refer to the brain’s “plasticity”, which is the brain’s capacity for an entire function to relocate to the opposite hemisphere if injury, disease or surgery destroy the part of the hemisphere where the function is mainly located.

THE END References: Grivas,J., Down, R. & Carter, L. (2004). Psychology: VCE Units 3& 4. (3 rd ed.)(85- 93). Melbourne: Macmillan Education. Milesi, P. & Vainer, L. (2005) Psych Notes Unit 3. 2 nd Ed. Victoria: A+ Publishing. Van lersel, Bradley, Coon, Houlihan, Koerner, Montalto, Rossborough & Stone. (2005) Nelson Psychology VCE Units 3 and 4. Melbourne: Thomson Nelson.