Basic strategies underlying facial perception? How are faces encoded? Does spatial recognition have a special status?... Determine this by asking is impairment of this capacity an autonomous deficit or one expression of a pervasive visuoperceptive disability
Failure to recognize or identify a visual stimulus w/ in the context of apparently adequate visuosensory capacity FACIAL AGNOSIA (prosopagnosia)- incapacity of patient to identify familiar faces on the basis of visual perception Caused by bilateral disease (lesion to inferior occipital area of right hemisphere) Simplest interpretation = impairment to analysis and synthesis of complex visual stimulus configurations that most clearly manifests itself in facial recognition because its such a formidable discriminative task (visuoperceptive disability)
Some prosopagnosia patients can identify unfamiliar faces quite well Patients with serve visuoanalytic and visuosynthetic capacity generally do not show facial agnosia There is something special about facial recognition and its disturbances
Incapacity to perceive individuality within a single class of objects Material specific defect in memory (defect in integrating current facial percepts with past experience of them) *no single explanation is supported with impressive empirical evidence b/c facial agnosia is too rare to accumulate ample data
Series of different facial recognition tasks given to brain-disease patients to determine relationship of performance level w/ locus of lesion. A.) matching of identical front-view photographs of a face B.) Matching of a front-view w/ views from different angles C.) Matching of front-view photographs under different lighting conditions
Right anterior Right posterior Left anterior (nonaphasic) Left posterior (nonaphasic) Left anterior (aphasic w/o comprehension defect) Left posterior (aphasic w/o comprehension defect) Left anterior (aphasic w/ comprehension defect) Left posterior (aphasic w/ comprehension defect)
Patients w/ posterior right hemisphere lesions & visual field defects performed at a lower level than the rest of the groups Among patients w/ posterior right hemi. Lesions, those w/ visual field defects showed higher frequency of failing facial recognition performance Only a minimal difference for patients w/ left hemi. Posterior lesions Injury to central visual pathways in not a determinant in failing performance on facial recognition in patients with posterior lesions Right hemisphere plays a particularly important role in mediating the discrimination of unfamiliar faces.
Group of patients with left hemisphere disease that show noticeably high frequency of failure in facial recognition (aphasic patients w/ defective aural lang. comprehension) Therefore, in addition to visuoperceptive mechanisms of the right hemisphere, mechanisms of the left hemi. are also involved in the discrimination of faces Left hemisphere = linguistic (verbal encoding of perceptions help out in facial recognition) ex: “long nose” “she’s pretty” “big ears”
Assumption that detection of familiar and unfamiliar faces relies on the same capacities proved incorrect Disabilities in identifying familiar and unfamiliar faces are dissociative Prosopagnosia patients can identify unfamiliar faces but not familiar faces. Prosopagnosia = bilateral disease (product of occipito-temporal disease) Incapacity to ID unfamiliar faces = unilateral hemispheric disease Impairment of facial recognition comes in 2 forms… Prosopagnosia and defect in discriminating unfamiliar faces.