The Dual Functions Of Sight - Perception And Action - Demonstrated For First Tim

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The Dual Functions Of Sight - Perception And Action - Demonstrated

For First Time

http://www.medicalnewstoday.com/medicalnews.php?newsid=39028

The dissociation in the visual system between two separate functions -

one that enables us to identify objects and the other to interact

with them - has been clearly demonstrated for the first time in

healthy humans by researchers at the Hebrew University of Jerusalem.

These separate vision-related actions have been documented from the

beginning of the 20th century in patients who suffered damage to the

visual system as a result of illness or injuries in which one or the

other function - identification or action - was damaged.

For example, persons suffering from ataxia are able to verbally

identify an object presented to them but have difficulty in grasping

it, while those who have agnosia can grasp an object if handed to

them but are unable to name or indicate the position, size or texture

of the object.

This dissociation between action and perception suggests the

existence of two separate visual streams However, despite the wide

research triggered by this theoretical concept, it had not been

proved in subjects in whom both streams are functioning normally.

Now, through the use of functional magnetic resonance imaging (fMRI),

Prof. Ehud Zohary and his graduate student Lior Shmuelof of the

Department of Neurobiology at the Silberman Institute of

Life Sciences at the Hebrew University have been able to demonstrate

dissociation between perception of objects and actions in the brains

of healthy persons. An article detailing their findings was published

as the cover story in the journal Neuron.

In the article, the researchers described how they were able to

observe dissociation between dorsal and ventral activation patterns

in the brains of participants who were shown video scenes of objects

and actions directed towards those objects.

What Shmuelof and Zohary saw in the fMRI images were that a complex

in the occipito-temporal cortex area of the brain responded to the

identity of an object presented on the screen, while a different

complex in the parietal lobe region reacted when the subjects were

shown actions directed at those objects.

The researchers point out that the areas of the brain responsible for

motor action were activated when the experimental subjects were shown

scenes of action, even though the subjects were in a passive state,

viewing only video clips presenting actions by others, and were not

involved in any way with the activities being screened.

What this suggests is that there is an interrelationship between

guiding of our own actions and understanding actions taken by others -

a kind of " stepping into another's shoes " that may be one of the

bases underlying social communication.