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15 Cards in this Set

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Model of Action Control

Blakemore, Wolpert & Frith (2002)

- action control involves integration of inverse model with a forward model.

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.

Efference Copy

When a motor command is sent to eye movements it is also sent back to visual representation.

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

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’

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

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.

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.

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.

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.

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.

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.

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)

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.

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.