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15 Cards in this Set
- Front
- Back
- 3rd side (hint)
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Model of Action Control |
Blakemore, Wolpert & Frith (2002) - action control involves integration of inverse model with a forward model. |
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Forward Model |
Uses efference copy to predict the sensory consequences of motor commands whenever movements are made. Predictions made by the forward model may be available to awareness. |
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Efference Copy |
When a motor command is sent to eye movements it is also sent back to visual representation. |
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Two types of predictions the Forward Model makes |
1.) Predicts the actual outcomes of the motor command and compares this to the desired outcome - this comparison occurs before a movement has been made. 2.) Predicts the sensory consequence of movement and compares this with the actual feedback - this comparison occurs after a movement is made.effer |
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Inverse Model |
Provides the motor commands necessary to achieve some desired outcome. Saccades are guided by visual goals, through a pathway from visual areas to motor areas. |
Model is a ‘guess’ |
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Abnormalities in awareness of action |
If part of these system doesn’t work, results in some of these abnormalities: - Optic Ataxia - Anarchic Hand Sign - Utilisation Behaviour - Phantom Limbs |
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Optic Ataxia |
Patients with optic ataxia fail to form representation of objects in the immediate environment in terms of the appropriate movements needed to reach and grasp them. - patient is aware of the impairment but cannot correct it. |
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Why and How and does Optic Ataxia occur? |
- Usually caused by damage to posterior parietal cortex. - Occurs because the inverse models are not properly finely ‘tuned’ by the immediate context. - The inverse models do not use the affordances offered by the shape of the object to be grasped appropriately when computing motor commands required to make an action. |
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Anarchic Hand Sign |
Inability to control action in accordance with goals. One hand is ‘out of control’ - a hand that moves of its own accord, without the will of the patient. - patient is aware of the impairment but cannot correct it. |
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Why and How does Anarchic Hand occur? |
- Usually caused by corpus collosum damage/ section or damage to supplementary motor area. - Occurs because the effects of the affordances supplied by the immediate visual environment are no longer inhibited by the currently intended action. |
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Utilisation Behaviour |
The site of an object elicits a stereotyped action, which is inappropriate in the wider context. The patient showing utilisation behaviour does not perceive a discrepancy between his actions and his intentions. Patient will ‘rationalise’ the behaviour. - Patient is therefore unaware of the impairment. |
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Why and How does Utilisation Behaviour occur? |
- Often due to frontal lobe damage - The problem causing Utilisation Behaviour occurs at an earlier stage in the development of an action than that causing the anarchic hand. - There is no awareness of goals and intended actions. - Patient is not aware of what he is going to do until he has done it. - Inappropriate responses elicited by objects in the environment are not inhibited. |
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Phantom Limb |
Motor commands to the absent limb lead to experience efference copy in somatosensory cortex and the sense the absent limb is moving. - coined by Mitchell (1872) |
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How and why does the Phantom Limb occur? |
After amputation to a limb, there is reorganisation of the deafferented region of the cortex. As a result, stimulation of the skin of distant areas such as the face or the chest can elicit sensations in a phantom limb. |
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Effects of Phantom Limb |
The mismatch between predicted and actual outcomes degrades the ability to move phantom which eventually gives rise to pain. - The pain can be burning, cramping, crushing or lancinating. |
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