the eye

Why do we need to move ours across a scene?

The information that is recorded in the retinal region only contains 50% of what is sent to the brain through the optic nerve.

When we move our eyes to focus on a specific region of an image or object, we are essentially placing the foveal region of the eye on top of the area which is currently within main focus of the lens in our eye. letting the foveal region register the image, the brain get the highest resolution possible for the image of the interesting area to process

·         The human visual field spans about 220 degree

·         divided in 3 main regions: foveal, parafoveal, and peripheral region

·         register visual data through the foveal region which constitutes less than 8% of the visual field

Would it not be easier if we could see the whole scene in front of us at once?

In order for us to accumulate all the information of a scene at one our skull need to be bigger as a normal size skull is unable to deal with all the information. In addition the high spatial resolution is located in a small section of the retina.

For this to be possible we would need to have slightly bigger eyes and brain to register the information that is sent. You would also need more reception and structures to process that information this would then increase the amount of neurons and photo receptor. Therefore this would increase the need to feed those neurons and photo receptor therefore incensement in energy consumption. Also you Need the photo receptor spread all across the retina not just in the fovea  you would need high density mean that you can get everything from the scene but you going to get lot of information that you do not need.

The brain consume a lot of energy glucose hungry structure – when looking an anorexic  person the brain and the cognitive activities  are normally ok  but the mussels fade away because  a lot so the energy that is need for  the brain is protected through evolutions . The energy that the brain is consuming is not going to be available muscles start to decrease. – When looking at extreme anorexia there are mechanism that are emplaces to  protect the brain as it steel the energy from other part of the body.

When the brain does not have the bare minimum that it need it put the body in a comma so it perceives it by not being active. You would not see an extremely hungry person that would be anxiety to find food but when the energy supply is so low they would enter a stage where they are unable to move and are waiting to die – this is seen with cases of extreme farming –no energy to move hence the reason why they do not get up and search for food.

Animals effect – we seen that some animal have smaller brain and bigger bodies this is because  the motor control that they have is smaller and the energy  that is consumed there the brain need less energy. Save energy by not having highly developed contrive skills

What does FEF mean? And what is its role in vision?

FEF it the abbreviation for frontal eye field it is located in the frontal cortex and controls generation for motor commands for pointing the eye and directing   the eye to desire location and play a role in directing spatial attention.

Topic of the week

Agnosia is a recognition disorder. Visual information is only useful when objects can be recognised by the brain. Brain damage can lead to several problems with the visual perception Visual Agnosia inability to recognize objects even though elementary visual functions remain unimpaired.

Can be broken down in to two subsections

·         Apperceptive Agnosia

Impairment occur during the perceptual processing

The case of HJA- he suffered from bilateral stroke was unable to recognise picture but give a reasonable description of it parts.

e.g.  a carrot – bottom bit seem solider the other bit seem feathery

Diagnosis is that his has difficulties in perceptual grouping mechanisms  

·         associative Agnosia

Impairment occurs during visual memory representation. (lissaure 180)

Object constancy – object remain the same even in different positions and lighting condition   

Studies have shown that they are able to name and recognise objects from a usual view rather than an unusual- (Humphreys& riddoch 1984)- this happen when there is damage to the right parietal lobes

The parietal lobes – may have mechanisms to extract the structure of an object and for rotating objects so that it can be identified at different view points

  

   Object Agnosia

Unable to decide the correct orientation of an object or whether the two objects presented have the same orientation even thought they can recognise the object.  

FMRI studies show that using pair of object that are different size and view point can test object constancy. For the reason that when the same object are pair repeatedly the response of the neuron decreases over time. Therefore you can correlate the different factors such as size and view point with the responses of the FMRI results.

Finding suggest that left infero – temporal region response irrespective of view point for size whereas view point was important for the comparable region in the right hemisphere

Prosopagnosia

The inability to recognise previous familiar faces.  

Face recognition – Bruce and Young (1986) the is a different between the process used to recognise familiar and unfamiliar faces.

Familiar faces are recognised by matching it to a stored face data base description

De Renzi (1986) – was unable to recognise some of his family members but was able to identify them through their voices and other non facial information

The fusiform face area in the right hemisphere may specialize in faces Kanwisher(2000)

Category perspective – a area of the brain that can recognise different categories of objects such as animal, face, body and words.

Further studies has identified that there are other part of the brain that is related to visual recognitions which is:

Parahippocampal- place are this is reasonable for scene that are more than objects and extrastriate body are – responds to the human body more than faces and objects.