Presentation on theme: "Prosopagnosia:. Prosopagnosia: Defined as a specific inability to recognise familiar faces. (Bodamer 1947). Contrasted with visual agnosia - inability."— Presentation transcript:
Prosopagnosia: Defined as a specific inability to recognise familiar faces. (Bodamer 1947). Contrasted with visual agnosia - inability to recognise objects by sight. Is prosopagnosia truly a "face-specific" disorder? Are prosopagnosics' problems confined to face recognition, or are they more general? Prosopagnosia could occur for various reasons - some more face-specific than others.
Testing for prosopagnosia: (a) Face identification: identify each of a series of famous faces; or decide which are famous, in a mixture of famous and non-famous faces. (b) Face matching: presented with two faces, have to decide whether they are two views of the same face or two views of different faces. (a)Is a more rigorous test, as (b) can often be done by picture matching. (However - Benton Facial Recognition Test: uses matching task, but target and foils differ in lighting and orientation).
Duchaine and Weidenfield (2003): WRMF can be performed on basis of non-facial cues. BFRT matching can be performed using eyebrows and hair. Unlimited time on each test - hence can be performed by laborious cross-checking. Problems with popular tests of face recognition: Warrington Recognition Memory for Faces: Which of these two faces has been seen before? Benton Facial Recognition Test: Which 3 faces match the top one?
Evidence that prosopagnosia is not due to perceptual problems or a generalised object agnosia: Sergent and Signoret (1992): R.M. prosopagnosic for faces, preserved recognition of cars. McNeill and Warrington (1993): W.J. prosopagnosic for human faces but not sheep faces. Moscovitch et al (1997) : C.K. agnosic for objects, but not prosopagnosic. Busigny and Rossion (2010): P.S. prosopagnosic, preserved object recognition.
Dissociations between face recognition and other aspects of face processing: 1. Dissociations between perception of age, gender, expression and identity: Tranel et al (1988), De Renzi et al (1989), Kurucz et al (1979). 2. Dissociations between perception of faces and other classes of objects: Bornstein (1963): ornithologist impaired at recognising birds but not faces. Bruyer et al (1983): farmer who could identify cows and dogs, but not faces. Assal, Facre and Anderes (1984): farmer who could identify faces, but not cows.
De Renzi, Faglioni, Grossi and Nichelli (1991): Distinguished between Apperceptive prosopagnosia: cannot produce a percept of a face. Associative prosopagnosia: cannot give any meaning to an adequate representation of an individual face. (Based on Lissauer’s 1890 distinction for agnosia).
The Bruce and Young (1986) model of face processing: Structural encoding: "this is a face" Face Recognition Units: stored faces Person Identity Nodes: access to semantic information Name Generation Expression Facial Speech Age, Gender Recognition
Prosopagnosia in relation to the Bruce and Young model: In theory, face recognition could break down at any stage: encoding, FRU or PIN - net result would be some form of prosopagnosia. “Apperceptive” prosopagnosia: Problems at the structural encoding stage? Bodamer (1947): Patient claimed all faces looked like "flat oval white plates with dark eyes" - unable to judge identity, age or sex of face. Humphreys and Riddoch (1987): HJA, an "integrative agnosic” - problems in integratng details into coherent wholes. Structural FRU PIN name
(b) “Associative” agnosia: Problems with FRU's, PIN's or the link between them? Adequate structural descriptions of faces (e.g. preserved matching of faces), but unable to link these to semantic knowledge about the person. Bauer (1984), Bruyer (1991), Bate (2011): Patients with implicit recognition of faces (priming, skin conductance) but no explicit recognition. Ellis and Young (1990): delusional misidentification syndromes (Capgras, Frégoli) - faulty links between face perception and familiarity. Structural FRU PIN name
(b) “Associative” agnosia (continued): Problems with FRU's, PIN's or the link between them? Problems with linking faces to names: Carney and Temple (1993): MH - prosopanomia. Structural FRU PIN name
Farah (1991): Examined 99 case studies. Little evidence that object agnosia could occur by itself, without either prosopagnosia or alexia. Proposes two processes: (a) holistic processing (for faces and objects): involves encoding complex shapes without decomposition into parts. (b) parts-based processing (for words and objects). Deficit in (a) = prosopagnosia. Deficit in (b) = alexia (inability to read). Claims prosopagnosia is an apperceptive disorder; careful testing reveals "associative" agnosics really have high-level perceptual problems.
Delvenne, Seron, Coyette and Rossion (2004): N.S. Agnosic and prosopagnosic. Bilateral occipito-temporal junction lesions from road accident; posterior occipital intact - no visual field loss. Formerly classified as an "associative" agnosic, on basis of normal drawing abilities and performance on some unspeeded neuropsychological tests. Careful testing ("clean" stimuli and RT measures as well as accuracy) reveals inability to perceive objects as integrated structures and hence difficulty in discrminating between objects with similar structure (e.g. cars, faces).
Delvenne et al (cont.): N.S. does not use relational processing. (a) No inversion effect in face- matching tasks (unlike normals). (b) Better at face matching if only isolated features are shown (normals: no difference).
PT - a developmental prosopagnosic: Retired schoolteacher - 55 year old right-handed male. University educated - OU Physics Tutor, with degree in Zoology and Biology. WAIS- III IQ 142, Verbal IQ 135, Performance IQ 140. Initially presented after an incident concerning students whom he couldn’t identify at school; has subsequently had to take early retirement. Normal in everyday activities, housework, cooking etc. CT scan revealed no obvious abnormalties.
Summary of testing with PT: Good at object naming, object semantics and object decision. Normal at matching unfamiliar faces. Poor at emotional judgements of faces. Poor at familiarity judgements of faces. Poor at face naming; better at naming other within- category objects (e.g. flowers).
Experiment 1 - Familiarity Judgment Experimental Condition NormalStretchedBlurredStretched and Blurred PT RT Errors (%) 1347ms ms ms ms 58.3 Controls RT Errors (%) (N= 27) 1148ms ms ms ms 22 Conclusion: PT copes well with stretching (anti-configural manipulation), but is at chance with blurred faces (anti-featural manipulation). Controls cope well with stretching OR blurring, but not both.
Experiment 2A - familiar face matching (effects of stretching) Experimental Condition Familiar Normal Familiar Stretched Experimental Effect PT RT Errors (%) 1351ms ms ms 0 Controls RT Errors (%) (N= 27) 1159ms ms ms 0 Conclusion: PT similar to normals - copes well with stretching, in a matching experiment.
Experiment 2B - familiar face matching (effects of stretching and blurring) Experimental Condition Familiar Normal Familiar Stretched and Blurred Experimental Effect PT RT Errors (%) 2023ms ms 50 N/A +50 Controls RT Errors (%) (N= 27) 844ms ms ms Conclusion: PT at chance with matching stretched and blurred faces. Controls unaffected by stretching and blurring.
Experiment 3A - Familiar flower matching (effects of stretching) Experimental Condition Flower Normal Flower Stretched Experimental Effect PT RT Errors (%) 1315ms ms ms 0 Controls RT Errors (%) (N= 15) 969ms ms ms Conclusion: PT similar to normals - copes well with stretching.
Experiment 3B - Familiar flower matching (effects of stretching and blurring) Experimental Condition Flower Normal Flower Stretched and Blurred Experimental Effect PT RT Errors (%) 1497ms ms ms Controls RT Errors (%) (N= 15) 980ms ms ms Conclusion: PT similar to normals – copes well with stretching and blurring of flowers. Blurring impairs PT’s face recognition much more than his flower recognition.
Conclusions: PT has a problem with configural processing - blurring impairs performance by preventing use of featural details. May be face-specific; he can process configural information from flowers (so not a generalised problem with within-class discriminations). Other prosopagnosics exist who appear to have a specific deficit in configural processing (but not necessarily face-specific)...
Barton et al (2003): Patient T.S. Unimpaired detection of single spatial changes (e.g. eye separation). Impaired “geometric context effect”. (Normals detect spatial changes that alter the eyes-mouth triangle faster than changes that do not). i.e. TS cannot form an integrated spatial percept. Same triangle (proportionately)
Lack of inversion effects in prosopagnosics: Stephan et al (2003): SC: impaired at within-class discriminations for faces, cars, fruit,veg. Matching individual facial features (pairs of eyes): 20/20 correct. Individual familiar face recognition: 1/25 correct. Nunn et al (2001): EP: slow at unfamiliar face matching. Normal for flowers, cars and buildings. Inversion effect with houses but not faces. Marotta et al (2002): CR: faster to match inverted faces than upright faces (perhaps inversion disrupts his malfunctioning configural processing). Busigny and Rossion (2010): PS.: no inversion effect or CFE for faces, reflecting inability to process faces configurally. Minimal low-level visual impairments.
Avidan, Tanzer and Behrmann (2011) Avidan, Tanzer and Behrmann (2011): 14 congenital prosopagnosics. No face inversion effect. Local bias with Navon letters. Less affected by composite face effect than normals.
VanBelle et al (2011) VanBelle et al (2011): Gaze-contingent masking study with patient GG. Delayed matching to sample: test face followed by a pair of faces. 3 conditions: (a)Full view; (b)Single feature; (c)Gaze-contingent masking. GG impaired with (c) but within normal range for (b) – implying featural but not configural processing
Busigny et al (2010) Busigny et al (2010): P.S. tested on within-class discrimination for faces and non-face objects. Delayed matching to sample. Non-face within-class discrimination OK; PS has an apparently face-specific impairment.
Different conceptions of featural and configural processing: Levine and Calvanio (1989), Farah et al (1995): (a) Featural (piecemeal) processing: for object recognition. (b) Configural (holistic) processing: for face recognition. Prosopagnosia is a loss of a face-specific configural processing system; a separate featural system for object recognition is left intact. de Gelder and Rouw (2000), Tarr and Gauthier (2000): Two modes of processing, used with both faces and objects. Configural processing is not specific to faces. No face-specific processor.
What is the anatomical basis of face recognition?: Early studies: suggested bilateral damage was necessary. Current view: right hemisphere seems particularly important for face-recognition: but unilateral RH or (more rarely) LH damage are sufficient for prosopagnosia. Farah (1990): 65% of 81 prosopagnosics had bilateral damage, 29% RH only, 6% LH only. RH important for configural processing, LH for featural?
TransaxialCoronalSagittal The fusiform gyrus: The parahippocampal gyrus: TransaxialCoronalSagittal
What does the fusiform gyrus actually do?: Activated bilaterally (but more on right) by upright and inverted faces. Responds to human, cat and cartoon faces, greebles (during most within-class discrimination tasks?) Not essential for face recognition - some prosopagnosics have damage to lateral occiptial cortex but not the FFA (Rossion et al 2003). Not sufficient for face recognition - some developmental prosopagnosics show apparently normal FFA activation (Avidan et al 2005). Inconsistent findings - only some studies find FFA differentially responds to familiar/unfamiliar faces. Left anterior middle temporal gyrus and temporal pole are more involved in recognition (i.e. memory).
Haxby, Hoffman and Gobbini (2000): Face recognition involves an extensively distributed processing network. Core system (face processing) and Extended system (retrieving non-visual information about a face).
Conclusions: Neuropsychological data suggest that (a) vision is modular - a set of processes, for different purposes. (b) object recognition can be selectively impaired at many stages, from initial structural description (apperceptive agnosia) to linking with semantic information (associative agnosia). (c) the same is true for face recognition; there are many different causes of "prosopagnosia“. (d) Van Belle et al (2011): holistic processing is mediated by a network of interdependent RH cortical areas.
Are faces "special"?: Yes in the sense that they require fine-grain within- class discriminations between category exemplars (e.g. individual faces). This type of processing may not be unique to faces; may be used with any stimulus class that requires subtle within-class discriminations (e.g. greebles, dogs, birds). Gauthier: = general-purpose object-recognition mechanisms, which are most often used with faces. Bentin: = face-specific mechanisms which can be adapted for use with other stimulus classes, given experience.