Congenital Prosopagnosia:

Congenital prosopagnosia: Face recognition impairment without any apparent deficits in vision, intelligence or social functioning, and in the absence of any obvious brain injury. Prevalence of about 2.5% in Caucasian and Hong Kong Chinese (Kennerknecht et al, 2006, 2008).

Face-specificity of congenital prosopagnosia: Mixed group. Some CPs are also agnosic for other within-class discriminations (e.g. specific cars, horses: retain basic-level recognition). Some CPs have deficits with recognition and other types of face processing (e.g. emotion or gender discrimination, Ariel and Sadeh 1996). Duchaine et al (2006): 1/3 have navigational difficulties, 1/5 have speech-reading problems in noisy environments. Some CPs have deficits confined to face recognition.

Causes of congenital prosopagnosia: 1. Genetic conditions: Runs in families (De Haan 1999, Greuter 2004, Greuter et al 2007). Autosomal dominant transmission (a point mutation as its basis). Duchaine, Germine and Nakayama (2007): Impaired identity perception, object processing; unimpaired global processing (Navon), emotion perception

Causes of congenital prosopagnosia: 2. Early visual problems: e.g. severe myopia or cataracts (Le Grand et al 2001; Le Grand, Mondloch, Maurer and Brent 2003). 3. Contrasts with "developmental" prosopagnosia - early brain damage?

Avidan, Thomas and Behrmann (2008): Performance of seven CPs on face recognition and matching tasks - perceptual impairment, not just impaired memory for names:

Jones and Tranel (2001): TA: 5 year old associative congenital prospagnosic. Unable to learn and recognise faces (including parents). Navigational difficulties. Normal for perception of emotional expression. Above-average visual naming of common objects. Superior reading, spelling and arithmetic; high IQ. Structural MRI showed no abnormalities. Poor overt recognition, but normal covert recognition (skin conductance):

Grüter, Grüter and Carbon (2008): Review attributes of 54 "hereditary" CPs. Characteristic deficit is uncertainty about face familiarity: mistakenly think strangers are familiar, and familiar faces are unfamiliar. Take longer to recognise familiar faces and to learn new faces. Abnormal eye-gaze patterns - more dispersed and more directed to external facial features. Frequent impairment in object and scene perception. No deficit in emotion perception, or judgments of attractiveness or gender.

Neural correlates of congenital prosopagnosia: Haxby, Hoffman and Gobbini (2000): "core" and "extended" systems in face processing.

Normal participants: (a) greater activity in core regions for faces than for non-face objects. (b) core regions show repetition suppression - attenuated activity in response to repeated facial information. - fusiform gyrus shows attenuation in response to identity repetition. - superior temporal sulcus shows attentuation in response to expression repetition.

Congenital prosopagnosics: fMRI studies are equivocal - many (but not all) show apparently-normal fusiform gyrus activity in congenital prosopagnosics (Avidan et al 2008). Furl et al (2011): Suggest continua both of impairment and FG activity, not an absolute deficit. 15 congenital prosopagnosics and 15 normals. As a group, CPs had reduced face-selective responses in bilateral FFA when compared with non-CPs. Individual CPs were also more likely than normals to lack expected face-selective activity in core regions.

Avidan, Hasson, Malach and Behrmann (2005): Congenital prosopagnosics show unimpaired RH functioning, but reduced LH activity in response to faces (especially in FG). Avidan and Behrmann (2007): Normal repetition-habituation effects in FFA of CP individuals. Dobel et al (2008): CPs show reduced M170, especially over LH.

Avidan, Thomas and Behrmann (2008): Reduced connectivity between FG and anterior temporal and frontal regions. CP have altered R and L inferior longitdinal fasciculus and inferior fronto-occipital fasciculus

Duchaine, Yovel, Butterworth and Nakayama (2006): Edward: Lifelong face recognition difficulties. Also problems with expression perception. No navigational difficulties. No face-selective M170. No inversion effect (unlike normals). Normal contrast sensitivity, BORB and naming of line drawings.

Edward's profile of impairment: Face naming test (black = Edward, grey = control participants) Face detection test: Edward 91.2% correct, controls 87.2% (i.e. unimpaired) Old/new discrimination test: black = Edward, (a) relative to average control performance, (b) in relation to individual control performances.

Normal greeble-learning abilities. Implies greebles are learnt using object- recognition systems, not face-processing mechanisms. Face vs body recognition

Edward's profile of impairment and its implications: Fairly specific problems with face recognition and emotion recognition. Normal-range performance with inverted faces and headless bodies shows he has no problems with low-level pattern recognition (e.g. curvature discrimination) or within-class discrimination generally. Normal second-order configural processing for houses but not faces - so no general configural deficit. Deficit seems to be at the structural encoding stage of face processing. Duchaine et al suggest Edward failed to develop a face-specific processing mechanism; this did not affect other object- recognition systems.

Lobmaier, Bölte, Mast and Dobel (2010) Lobmaier, Bölte, Mast and Dobel (2010): Compared 6 CPs to 6 normals on tests with normal, blurred and scrambled faces, houses and sugar-bowls. If CP is a process-specific difficulty (configural processing), should be impaired on all blurred conditions, unimpaired on all scrambled conditions. Sequential same-different task - manipulated stimulus, always followed by an intact stimulus. Severely impaired with blurred faces, but not houses or bowls. Concluded CPs have a face-specific deficit, most pronounced for configural information (but can use configural information in other stimulus types).

Face-specificity of congenital prosopagnosia: Germine, Cashdollar, Düzel and Duchaine (2011): A.W. : 19-year old female, discovered by web-based screening. Developmental associative agnosic - not prosopagnosic. Selectively impaired for remembering guns, horses, scenes, tools, doors, and cars. Normal on 7 tests of face recognition, plus memory for houses and spectacles. Normal at matching visual shapes (faces, bodies, objects - i.e. has a memory deficit, not a perceptual deficit). Structural MRI revealed no abnormalties; no familial history. Implies development of face recognition and object recognition are separate processes - normal face recognition can develop even if object recognition is impaired.

Face-specificity of congenital prosopagnosia: "Doors and people" test: AW in normal range, except for door recognition!

A.W.'s deficit is unclear; impaired object recognition but puzzling why house and spectacles recognition are not impaired too.

Conclusions: Congenital prosopagnosia is evidence for the domain specificity of face recognition. Suggests face recognition is produced by mechanisms that are largely uninvolved in the development of other visual recognition systems (otherwise CPs would be agnosic too). Specific developmental disorders (CP, dyslexia, dyscalculia) imply that other, unrelated systems can develop normally. Specificity of CP impairment, in absence of brain damage, provides useful opportunities to investigate neural substrate of face processing. FFA is necessary but not sufficient for normal face processing. Heterogeneous group: some appear to have configural processing deficits, others a more associative deficit.