Study Design Content

Study Design Content• contribution of studies to the investigation

of cognitive processes of the brain and implications for the understanding of consciousness including:

– studies of aphasia including Broca’s aphasia and Wernicke’s aphasia

– spatial neglect caused by stroke or brain injury

– split-brain studies including the work of Roger Sperry and Michael Gazzaniga

– perceptual anomalies including motion after-effect, change blindness, synaesthesia1

Studies on Cognitive Processes of the BrainAphasia

Broca’s aphasiaWernicke’s aphasia

Spatial Neglect

Split-Brain studies

Perceptual anomaliesMotion-after effectChange blindnessSynaesthesia

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AphasiaThe term aphasia is a general term used by clinicians

to describe individuals with a language disorder

Neuropsychologists commonly define aphasia more specifically to refer to a language disorder apparent in speech (comprehension or production), writing or reading produced by injury to brain areas specialised for these functions

The common cause of aphasia is a stroke to a particular part of the brain which is involved in language production or comprehension

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Aphasia

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Broca’s AphasiaDamage to Broca’s area, in the left frontal lobe next to

the motor cortex, leads to a person having difficulty speaking, although their ability to comprehend and understand speech is unaffected

Speech often consists of very few words, and usually only nouns and verbs are spoken

Most people with Broca’s aphasia are aware of their language difficulties and have a relatively clear understanding of their condition

Video clip - Individual with Broca’s aphasia

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Wernicke’s AphasiaWernicke’s aphasia is a type of aphasia in which

individuals have great difficulty in comprehending speech and speaking in a comprehensive way

This type of aphasia is usually a result of damage to Wernicke’s area, located in the temporal lobe of the left hemisphere

Unlike someone with Broca’s aphasia, speech is fluent and grammatically correct, but what is said is incomprehendible and is generally nonsense words and phrases

Unlike people with Broca’s aphasia, individuals with Wernicke’s aphasia have little awareness or understanding of their condition

Video clip – Individual with Wernicke’s aphasia6

Spatial NeglectGenerally spatial neglect is an attentional disorder

where an individual fails to acknowledge anything on their left or right side and they tend to behave as if that particular side of their world does not exist

This disorder is most frequently seen in stroke or accident victims who have extensive damage to the rear part of the right parietal lobe – this means that these individuals mostly neglect the left side of their world

Spatial neglect to the right side sometimes occur after similar damage to the left side but is much less frequent and milder

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Spatial Neglect

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Spatial NeglectSpatial neglect is a complex disorder with many

subtypes – although it usually occurs in a visual sense, it may occur for other senses such as hearing, touch or movement

It may also be isolated to one or a combination of senses

The extent of neglect varies between patients and depends on the severity and exact location of the damage – some patients recover gradually from the disorder as seen in Figure 4.40 on page 219

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Split-Brain StudiesSplit-brain surgery involves surgically cutting the corpus callosum

(and sometimes other nerves connecting the hemispheres), effectively severing the connection between the left and right hemispheres

This was often used as a treatment for epilepsy as the electrical activity in the brain which causes the problem would be able to move throughout the brain via the corpus callosum and affect the whole brain, often resulting in violent seizures

Initially split-brain surgery was deemed not to have been a success as the seizures still persisted and it was abandoned

Later research by a famous psychologist Roger Sperry and his student Ronald Myers on the effects of split-brain surgery on cats led two American neurosurgeons to reconsider the treatment on patients – they reasoned that some of the earlier work had failed because the connection between the hemispheres was not complete

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Split-Brain StudiesBogen and Vogel performed split-brain

surgery on 11 epileptic patients each time cutting the corpus callosum and some of the other nerves connecting the hemispheres

The procedures were successful leaving the individuals virtually seizure free and with minimal side effects

Roger Sperry and Michael Gazzaniga performed extensive research on these 11 patients to test the effects the split-brain surgery had on their brain and hemisphere connection

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Sperry and Gazzaniga

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Sperry and GazzanigaSperry and Gazzaniga tested all 11 of the split-brain patients as

well as individuals with their corpus callosum intact

Each participant was seated behind a screen which is used to flash a word or picture for a fraction of a second while the individual focuses on a black dot in the mid-point of the screen. The work or picture is flashed to either the left or right of the black dot

Visual information flashed to the left of the black dot is in the participants left visual field and is therefore sent to the right hemisphere, while visual information flashed to the right of the black dot is in the participants right visual field and is therefore sent to the left hemisphere

Behind the screen and hidden from view are several object such as an apple, spoon and pencil – although they are hidden from view, the participant may reach under the screen and touch them therefore experience tactile sensation if they are able to do so13

Sperry and Gazzaniga When an object was flashed to the screen, Sperry would ask, “What did

you see?”

In response to images flashed to the right visual field (and sent to the left hemisphere), the participants could name the objects but when the object was flashed to the left visual field (and sent to the right hemisphere), the participant could not say what they had seen and often denied anything had been flashed on the screen other than a ‘flash of light’

If the visual information in the right hemisphere cannot cross back into the left hemisphere (because the corpus callosum has been severed) the participant could not say what they had seen

This is because the control of speech is located in the left hemisphere

In order to be sure the participant did see the object Sperry asked the participants to locate the object under the table using their left hand which they could correctly do because their left hand is controlled by their right motor cortex in the hemisphere that also saw the image of the object

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Sperry and GazzanigaIt is evident that the right hemisphere had processed the

information about what the participant had seen because they could correctly locate it using their left hand

However, the participant could not say what the object was because language is controlled by the left hemisphere and only the left hemisphere could convert the information into spoken words

This research provided indications of specialised functions by the hemispheres as well as the role of the corpus callosum in exchanging information between the hemispheres of the brain

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Sperry and GazzanigaThe two hemispheres can compensate for the

absence of a corpus callosum and other neural connections

Most tasks are involved in both hemispheres and although one hemisphere may specialise in a task it does not mean that the task is performed exclusively in that hemisphere

Video clip - Michael Gazzaniga performing research on a split-brain individual

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Perceptual AnomaliesPerception occurs when sensory information reaching

the brain is meaningfully interpreted

The term perceptual anomaly is used to refer to an irregularity in perception and usually involves a mismatch between the perceptual experience and physical reality

We will examine three examples of perceptual anomalies involving the perception of movement (motion after-affect), failure to see something that actually takes place (change blindness), and a perceptual anomaly that involves unusual experiences in one sense when another sense is stimulated (synaesthesia)

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Motion After-EffectMotion after-effect is the perceptual illusion of

movement of a physically stationary visual stimulus following exposure to visual motion

The stationary stimulus appears to move in the opposite direction to the original (moving) stimulus

It was first mentioned by philosopher Robert Addams who was staring at a waterfall when he noticed that when he shifted his gaze to the surrounding rocks, they appeared to move upwards – Addams referred to this as the waterfall illusion

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Motion After-Effect

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Motion After-EffectResearch indicates that eye movements and

neurons in the visual cortex specialised to detect and respond to motion are directly involved in the illusionary effect

Studies have also found that there are neurons in the visual system which are sensitive to the direction of movement

Illusions such as the motion after-effect show us that perception, although reliable, may not always reflect reality

Box 4.13 – Case study of akinetopsia – motion blindness, pg. 227

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Change BlindnessBefore we talk about change blindness, lets

watch a short video

Video clip - The Monkey Business Illusion

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Change BlindnessChange blindness refers to the difficulty which

individuals have in noticing large changes to visual scenes

Research indicates that we experience a remarkable lack of awareness of events that take place in our visual environment

Change blindness occurs when both change is expected and unexpected

When it is expected, we may eventually detect the change but it can take an astonishingly long time to do so, even for large changes

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Change BlindnessFor change blindness to occur it has to

involve some kind of visual disruption, such as brief obstruction during an eye movement.

This means that change blindness is different from inattentional blindness which is a failure to notice something in a scene when the same scene continually remains in view

Video clip - Change blindness23

Change Blindness American psychologist Ronald Rensnik (1998) examined

whether an observer is able to sense that a change is occurring even though they have no visual experience of the change

Rensink used a flicker technique where observers were shown a flicker sequence in which an image of a real-world scene alternated with a similar image that had been changed

Observers pressed a button first when they were aware that something was changing and second when they visually experienced the change

14 of the 40 observers reported ‘feeling’ that something was changing in a large number of trials

The results show that some individuals have a conscious experience of change without an accompanying visual experience24

SynaesthesiaSynaesthesia is a perceptual experience in which stimulation of a

particular sense elicits an additional unusual experience in another sense - the additional experienced sense adds to the overall perception without replacing the initial sense

Researchers have found that synaesthesia is a real experience rather than an imagined one and can be distinguished by a number of characteristicsIt is involuntaryIt is very difficult to suppressThe experience is highly vivid, memorable and consistent across timeAlthough consistent for each individual, the condition varies between

sufferersThe condition tends to be one-way rather than bi-directional so if a

sound produces a taste sensation this does not mean a taste will produce a sound sensation

Video clip - Synaesthesia25

SynaesthesiaOne of the most common forms of synaesthesia

is known as grapheme-colour synaesthesia and occurs when the viewing of letters or numbers produces the experiences of colours

Figure 4.53 shows a common strategy used to test grapheme-colour synaesthesia – the participant is presented with a pattern of triangular H’s and is asked to identify the triangle

Most individuals have difficulty locating the triangle but individuals with synaesthesia can often easily locate the triangle as each letter appears as a colour making it more easily distinguished

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SynaesthesiaThere is still relatively little known about

synaesthesia and why it is experienced

Some think that individuals with the condition are unusually sensitive to external stimuli while others feel it may be a result of a breakdown in sensory and perceptual processes

Most psychologists agree that the brains of individuals with the condition possess unique structural and/or functional qualities

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