Prosopagnosia:

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): Does "associative" prosopagnosia really exist? 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 an apperceptive disorder - 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 configural 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).

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.

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?

"What" and "where" pathways in the visual system:

TransaxialCoronalSagittal The fusiform gyrus:

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 (i.e., during most within-class discrimination tasks?) Not sufficient for face recognition - some prosopagnosics have damage to lateral occipital cortex but not the FFA (Rossion et al 2003). Not essential 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).

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.