Objects and Faces: The Neuropsychology of Agnosia and Prosopagnosia

1. Objects and Faces: The Neuropsychology of Agnosia and Prosopagnosia http://www.neuro.spc.org/bbk Vaughan Bell vaughan@backspace.org

2. Outline • Visual Agnosia- A deficit in object recognition. • Neuropathology of Visual Agnosia. • Prosopagnosia- A deficit in face recognition. • Neuropathology of Prosopagnosia. • Implications for normal functioning: • Do we have separate systems for object and face recognition ? • Farah’s dual system model. • Some problemas with Farah’s theory.

3. Visual Agnosia Definition • Visual Agnosia is a deficit in object recognition and identification. • In the absence of any significant damage to the early visual system (eye, retina, optic nerve, LGN etc). • And without intellectual impairment.

4. Early work • Lissauer’s (1890) account of agnosic patients was one of the earliest reports of the agnosic syndrome. • He noted differences in the behaviour of different agnosic patients and also differences in performance on the same task on different occasions. • He proposed a two part classification for agnosia.

5. Lissauer’s Classification • Apperceptive agnosia: A failure of object recognition in which perceptual impairments seem to be the primary cause of disruption. • Associative agnosia: A failure in the object recognition process after the construction of a perceptual description. An inability to match perception to semantic properties in memory.

6. semantic access Apperceptive Agnosia Associative Agnosia Lissauer’s Classification This implies a simple two stage model of recognition. Perception Memory

7. Apperceptive Agnosia • It has been argued that apperceptive agnosics cannot assemble an appropriate perceptual description that would allow recognition to take place. • Apperceptive agnosic patients may be unable to complete Efron’s (1968) shape matching task where a same-different judgement is required.

8. Efron’s (1968) Shape Task

9. Apperceptive Agnosia • A less severe deficit may be seen experimentally. • Patients may be able to name objects from normal views. • But not from abnormal views or when dark shadows are cast.

10. Unusual Views Usual view Unusual view

11. Uneven Lighting Even lighting Uneven lighting

12. Associative Agnosia • A visual percept needs to be understood in terms of it’s meaning as well as it’s visual properties. • Associative agnosics seem to have problems more toward this stage of the object recognition process, than the perceptually weighted problems of apperceptive agnosics.

13. Associative Agnosia • Teuber (1968) described the associative agnosic experience as: • “a normal percept stripped of it’s meaning” • However, there is now a great deal of evidence to suggest that associative agnosics do not experience normal perception.

14. Copying Task • A classic distinguishing test is a picture copying task. Broadly speaking: • Apperceptive agnosics cannot successfully copy pictures because of their perceptual impairment. • Associative agnosics can copy pictures. It was originally argued that this demonstrated intact perception.

15. Copy by Patient HJA From Humphreys and Riddoch (1987)

16. Picture Matching Task • Again broadly speaking: • Apperceptive agnosics cannot successfully match pictures. • Associative agnosics can match pictures by visual appearance by not semantic similarity.

17. Picture Matching Task Apperceptive agnosic ‘Mr S’ From Benson and Greenberg (1969)

18. Associative Perceptual Problems • Originally it was thought the performance of associative agnosic patients on these tests demonstrated intact perception. • However, there is now a large amount of data to suggest this is not the case. • Although accurate, copying tasks may take an inordinate amount of time (6 hours !). • Performance is described as slavish, effortful, and ‘line-by-line’

19. Associative Perceptual Problems • Ratcliffe and Newcombe (1982) reported patient MS could make accurate copies but not distinguish between ‘possible’ and ‘impossible’ objects.

20. Associative Perceptual Problems • Rubens and Benson (1971) reported that their patient would sometimes confuse print imperfections with the picture. • Levine (1978) patient would make mistakes in a matching task when pictures were complex of differed only subtly from each other. • These problems would seem to suggest Lissauer’s original classification is not accurate.

21. Associative Perceptual Problems • Farah (1990) argues that whilst the ‘apperceptive’ and ‘associative’ labels are still useful… • …they should be used to describe agnosias with differing amounts of damage to the perceptual system. • Rather than discrete disorders in themselves. • This also suggests the simple model of object recognition is far too simple.

22. Neuropathology • Apperceptive agnosia: • Tends to result from diffuse / widespread damage to the occipital lobes. • Particularly after bilateral damage. • Carbon monoxide poisoning is relatively common, the occipital lobes seem particularly vulnerable to this.

23. Neuropathology • Associative agnosia: • Diffuse cerebral damage also implicated. • Left hemisphere damage more common than right. • Alexander and Albert (1983) argue that bilateral damage to the tempero-occipital junction is particularly common.

24. Human Brain

25. HJA’s CT Scan From Humphreys and Riddoch (1987)

26. Prosopagnosia • First used by Bodamer in 1947. • He described an injury to a 24 year old man who suffered a bullet wound to the head. • He became unable to recognise his friends and family, and even himself. • He was able to recognise them by voice, touch or other visual stimuli such as gait and physical mannerisms.

27. Prosopagnosia • Often accompanies visual object agnosia. • Although it can be seen in isolation such as Whitely and Warrington’s (1977) patient. • There seems to be dissociations between different processes in face recognition, and hence in prosopagnosia.

28. Young et al (1998) • Documented dissociations in face processing in a group of ex-servicemen with focal lesions from bullet wounds. • They found evidence for selective deficits in: • emotional expression perception • recognition of familiar faces • matching of unfamiliar faces • Although the last two were not independent.

29. Other deficits in Prosopagnosia • Concurrent deficits have also been found e.g.: • cows (Bornstein et al, 1969) • plants (Whitely and Warrington, 1977) • buildings (Gomori and Hawlyuk, 1984) • cars (Damasio et al, 1982) • Does this mean we have a cognitive module, or part of the brain dedicated to cow recognition ?

30. Neuropathology • Prosopagnosia: • Less likely to be diffuse than agnosia lesions. • Generally agreed a right hemisphere lesion is needed. • Although it is argued whether unilateral or bilateral lesions most commonly cause the impairment.

31. Neuropathology • De Renzi (1986) reported on two patients with unilateral damage. CT scans from case 2

32. Neuropathology • Damasio (1985) has argued that bilateral lesions are necessary. • And that patients like De Renzi’s may have undetected bilateral damage.

33. Neural Substrate in Normals • Functional imaging has allowed us to see which areas of the brain may be activated when viewing face stimuli. • Part of the fusiform gyrus, sometimes called the fusiform face area (FFA) is particularly active during this task.

34. George et al (1999) fMRI

35. Video

36. Implications for Normal Functioning • By examining the effects of brain injury on object recognition we can uncover the structure and function of normal processes. • It was suggested that faces are just more difficult than objects. • This should only result in a single dissociation. • However, we have seen a double dissociation for face recognition after brain injury.

37. Farah’s Two Component Theory • Farah (1990) considered agnosia and prospagnosia with another visual recognition disorder, that of alexia. • Alexia is a reading disorder, sometimes called ‘letter-by-letter reading’. • Alexic patients can understand single letters, but cannot recognise whole words.

38. Farah’s Two Component Theory • Farah argues alexia is a problem with assembling multiple parts in a whole. • When recognising words details are essential because changing one letter does not necessarily form a word of a similar meaning.

39. Farah’s Two Component Theory • Farah argues prosopagnosia is a problem with understanding the overall structure (a perceptual whole) of an object. • Details of individual parts of a face don’t contribute much to the recognition processes. • i.e. noses all look pretty similar. • It’s only when we combine these features in a face like shape that faces become distinctive.

40. Thatcher Illusion: Upside Down

41. Thatcher Illusion: Right Way Up

42. Farah’s Two Component Theory • Farah examined 99 case reports of patients with visual recognition disorders. • And found although face, object and word recognition all dissociate in pairs. • There are certain combinations that are very rare.

43. Rare Deficit Combinations Faces Objects Words prosopagnosia agnosia alexia - * * - - *

44. Farah’s Two Component Theory • Farah argued that this data can be explained by postulating two recognition systems rather than three. • One for perceiving perceptual wholes. • The other for multiple parts. • An object may require one, or the other, or a combination.

45. Farah’s Two Component Theory Faces Objects Words prosopagnosia agnosia alexia System for perceiving wholes System for perceiving parts

46. Predictions • Agnosia should not exist on it’s own, by definition it should entail damage to the system for either parts (words), wholes (faces) or both. • A patient with alexia and prosopagnosia must have agnosia, as the two supporting system are damaged.

47. Mr W - A troublesome patient • Ruminati et al (1994) reported on an agnosia patient, Mr W. • He seemed to have a selective deficit in object recognition. • But a preserved capacity to recognise faces and read printed text. • However, it was noted he made more semantic than visual perceptual errors.

48. Farah’s (1997) Reply • Farah (1997)argued that Mr W had a problem with memory, rather than visual perception. • And his object recognition deficits were due to a damaged knowledge store. • And so couldn’t be considered to be agnosic. • However, Ruminati and Humphreys (1997) argued that Mr W’s problem on an object matching task did show a perceptual deficit.

49. MH - another counter example ? • Humphreys and Ruminati (1998) reported on an agnosic patient with a selective deficit for objects. • Who does make visual, rather than semantic errors. • Suggesting her deficit is genuinely one of perception. • This may provide real problems for Farah’s model.

50. Conclusions • Apperceptive and associative agnosia seem to be differentiated by the amount of damage to the perceptual system. • The notion that associative agnosics have no perceptual deficits is now considered false. • Agnosia often results from diffuse, bilateral damage to the occipital lobe.