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Visual Agnosias

Explore the theories of perceptual organization and the development of perceptual abilities, including depth perception. Learn about visual agnosias and their impact on face recognition, with case studies and explanations of prosopagnosia.

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Visual Agnosias

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  1. Visual Agnosias • Specification: Theories of perceptual organisation • Gregory’s top down/indirect theory of perception • Gibson’s bottom up/direct theory of perception Development of perception • The development of perceptual abilities, including depth/distance, visual constancies. • Perceptual development, including infant and cross-cultural research Face recognition and visual agnosias • Bruce and Young’s theory of face recognition, including case studies and explanations of prosopagnosia

  2. Visual Agnosias • Learning Objectives • To define what is meant by visual agnosias, particularly prosopagnosia • Outline the difference between apperceptive and associative agnosia • To understand how the study of people with Prosopagnosia contributes to face recognition research.

  3. Visual agnosia • Comes from the Greek word for ‘not knowing’- refers to being able to see things but not recognise them. • People cannot extract meaning from what they see. • Individuals cannot name or select objects from a tray but they can use objects-e.g. throw a ball. https://www.youtube.com/watch?v=ze8VVtBgK7A

  4. Kinds of Agnosia • Apperceptive Agnosia • Associative Agnosia

  5. Apperceptive or Associative? • Apperceptive agnosias (also known as visual space agnosias) refer to a condition in which a person fails to recognize objects. Apperceptive agnosics are unable to distinguish visual shapes and so have trouble recognizing, copying, or discriminating between different visual stimuli. When patients are able to identify objects, they do so based on inferences using colour, size, texture and/or reflective cues to piece it together.

  6. Apperceptive Agnosia • For example, in the image below, an apperceptive patient may not be able to distinguish a poker chip from a scrabble tile despite their clear difference in shape and surface features.

  7. Associative agnosia • Associative agnosias are also known as visual object agnosias. • Can draw objects, match similar objects and describe component parts. • Although they can present with a variety of symptoms, the main impairment is failure to recognize visually presented objects despite having intact perception of that object. A patient with an associative agnosia may be able to replicate a drawing of the object but still fail to recognize it. Errors in misidentifying an object as one that looks similar are common.

  8. "recognition without meaning". • Patients with associative agnosias can copy pictures and match pictures but can’t associate these details with stored knowledge about the objects. Associative Agnosias

  9. Case Study- HJA- Associative Agnosia • Had a stroke, he could copy and match objects but couldn’t name them. • Couldn’t find the upside down letter T amongst lots of normal ones- because he can’t group things? • Whole faces poor, individual feature ok

  10. Case Study- JBR • Difficulties indentifying different classes of object • Non living things- 90% recognised • Living things- 6% recognised

  11. Prosopagnosia A visual agnosia where damage is explicit to the fusiformgyrus area of the brain. Objects are recognised, but not faces. https://www.youtube.com/watch?v=iwMuLF2M0T0 https://www.youtube.com/watch?v=dxqsBk7Wn-Y

  12. Prosopagnosia • Prosopagnosia (sometimes known as face blindness) is a disorder of face perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact. The term originally referred to a condition following acute brain damage, but recently a congenital form of the disorder has been proposed, which may be inherited by about 2.5% of the population. The specific brain area usually associated with prosopagnosia is the fusiform gyrus.

  13. De Renzi and di Pellegrino (1998)-Patient VA who had intact object recognition but couldn’t name faces. • Bruyer et al Mr W a prosopagnosic farmer couldn’t recognise human faces but could recognise his individual cows!

  14. Prosopagnosia • There are two explanations of prosopagnosia; • A unique face–specific problem • A number of fMRI studies show that the right fusiformgyrus is activated during face recognition, but much less so during object recognition. • Not a face-specific problem • Research using brain-imaging techniques sows that; • Some people with prosopagnosia have problems that extend beyond face recognition. • Holistic processing and activation of the fusiformgyrus are associated with recognising objects with which we are familiar or have particular expertise. This may include faces.

  15. Is it a unique face-specific problem? • Barton found that the fusiform face area (FFA) – see diagram in your notes, was damaged in people with prosopagnosia but less so in patients with object recognition problems. • Farah argues that face recognition is different to other forms of recognition – faces are special, and are processed separately from objects, this process can be selectively damaged.

  16. Not a face-specific problem • This is the opposite view, according to Gauthier (1999) people with prosopagnosia can have other object recognition problems. • The Bruce and Young model insists that faces are processed in a modular way but there is an alternative argument for holistic processing, where recognition is made using the overall shape and structure of objects and faces.

  17. Evaluation • Case studies dominate research in this area. Theses patients work with one researcher so corroborative evidence is lacking, Farah claims this is a lack of inter-laboratory verification. • PET and fMRI scanning shows brain activity in living patients, it can provide scientific evidence but there is still much to be learnt about the interpretation of these scans and their relevance to prosopagnosia.

  18. Farah (1995) case study L.H. fully supports specific mechanisms for face recognition as he could identify objects but not faces. However other case studies disagree. • Gradually there is an accumulation of evidence to support the view that faces are not special. Gauthier and Tarr (2002) argue that it comes down to expertise, the FFA is activated when tested on things people know a lot about, e.g. in birdwatchers it would be birds, not cars. • Eysenck argues that faces are not as special as psychologists once thought they were.

  19. What can you do about it? • Few successful therapies have so far been developed for affected people, although individuals often learn to use 'piecemeal' or 'feature by feature' recognition strategies. This may involve secondary clues such as clothing, hair color, body shape, and voice. Because the face seems to function as an important identifying feature in memory, it can also be difficult for people with this condition to keep track of information about people, and socialize normally with others. http://en.wikipedia.org/wiki/Prosopagnosia

  20. Visual Agnosias • Learning Objectives • To define what is meant by visual agnosias, particularly prosopagnosia • Outline the difference between apperceptive and associative agnosia • To understand how the study of people with Prosopagnosia contributes to face recognition research.

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