Abstract
We present an extensive investigation (24 experiments) of a new case of prosopagnosia following right unilateral damage, GG, with the aim of addressing two classical issues: (1) Can a visual recognition impairment truly be specific to faces? (2) What is the nature of acquired prosopagnosia? We show that GG recognizes nonface objects perfectly and quickly, even when it requires fine-grained analysis to individualize these objects. He is also capable of perceiving objects and faces as integrated wholes, as indicated by normal Navon effect, 3D-figures perception and perception of Mooney and Arcimboldo face stimuli. However, the patient could not perceive individual faces holistically, showing no inversion, composite, or whole-part advantage effects for faces. We conclude that an occipito-temporal right hemisphere lesion may lead to a specific impairment of holistic perception of individual items, a function that appears critical for normal face recognition but not for object recognition.
. Introduction
The ability to recognize people from their face is a fundamental brain function which holds a high social value. It is also an extremely complex function, which is nevertheless performed quite well in human adults. The adult human brain has developed mechanisms allowing, for instance, recognizing a familiar person from its face in less than half a second (Bruce & Young, 1986), or encoding new faces in memory effortlessly during the entire life (e.g., Bahrick, Bahrick, & Wittinger, 1975). Yet, interestingly, the field of face recognition was originally based upon the study of people who, following brain damage, have lost this expertise in recognizing faces.
Difficulty in face recognition as a major symptom in patients with cerebral disease was first reported in the nineteenth century (Charcot, 1883, Quaglino and Borelli, 1867, Wigan, 1844 and Wilbrandt, 1887). However, it was Bodamer (1947) who proposed to isolate the disorder on the basis of three cases, and introduced the term prosopagnosia from the Greek “prosopon” (face) and “a-gnosia” (without knowledge). Prosopagnosia is classically defined as the inability to recognize individual faces following brain damage, an impairment that cannot be attributed to intellectual deficiencies or low-level visual problems ( Benton, 1980, Bodamer, 1947, Hécaen and Angelergues, 1962 and Rondot and Tzavaras, 1969). Prosopagnosic patients also generally still retain their ability to recognize people by other cues: the voice or other visual traits such as gait, size, clothes, or even facial features (moustache, scar, freckles, …) or accessories (ear-rings, eyeglasses, piercings, …).
Over the years, tens of cases of prosopagnosia following brain damage have been reported, although extensive neuropsychological investigations of prosopagnosic patients remain quite rare (e.g., Anaki et al., 2007, Barton, 2008a, Delvenne et al., 2004, Lhermitte et al., 1972, Riddoch et al., 2008, Rossion et al., 2003, Sergent and Signoret, 1992a and Sergent and Villemure, 1989).
Both in traditional (cognitive) neuropsychology and in modern cognitive neuroscience, the lesion method is seen as an invaluable and unique way of understanding normal brain function (e.g., Caramazza, 1986, Damasio and Damasio, 1989, Farah, 1990, Farah, 2004, Humphreys and Riddoch, 1987 and Shallice, 1988), in particular with respect to face recognition. Such patient studies contribute to shaping our knowledge and conceptions of the processes involved in normal face recognition and their underlying neural networks.
From a functional point of view, there are two main debates concerning prosopagnosia, which have direct implications for understanding face recognition: (1) Can the impairment truly be restricted to face recognition (i.e. face-specific)? (2) What is the nature of the disorder, that is, what is at the heart of our expertise in facial recognition, and which is lost in these patients? These two issues have proved quite difficult to resolve and are still debated (e.g., Barton, 2009, Damasio et al., 1982, De Renzi, 1986a, Hécaen, 1981, Riddoch et al., 2008, Rondot and Tzavaras, 1969 and Sergent and Signoret, 1992a).
