نگرش ضمنی در پروزوپاگنوزیا

Abstract We studied a male with acquired prosopagnosia using a battery of Implicit Association Tests (IATs) to investigate whether observing faces varying by social category would activate the patient's implicit social biases. We also asked him to categorize faces explicitly by race, gender, and political party. The patient, G.B., was marginally slower to categorize black compared to white faces. He showed congruency effects in the race and celebrity IATs, but not in the gender or political IATs. These results indicate that G.B. possesses an implicit social sensitivity to certain facial stimuli despite an inability to overtly recognize familiar faces. The results demonstrate that social biases can be retrieved based on facial stimuli via pathways bypassing the fusiform gyri. Thus the IAT effect can be added to the list of covert recognition effects found in prosopagnosia.

. Introduction Prosopagnosia, an inability to recognize familiar faces due to neurological damage (Bodamer, 1947; see also Ellis & Florence, 1990), can be observed in brain-damaged patients even when vision, intelligence, and cognitive abilities remain normal (Sorger, Goebel, Schiltz, & Rossion, 2007). The associated brain damage is generally found in inferior temporo-occipital regions (Barton, 2008a, Damasio et al., 1982, Haxby et al., 2000 and Meadows, 1974), especially the fusiform face area (FFA), a region specialized for face perception (Haxby et al., 2000, Kanwisher et al., 1997 and Kanwisher et al., 1999). The FFA is connected to the middle temporal lobe, which represents semantic information about other people (Gorno-Tempini et al., 1998) and to the left anterior temporal pole, which mediates name retrieval (Grabowski et al., 2001). These regions are important in recognition of familiar faces (Schweinberger & Burton, 2003). Prosopagnosia is often associated with other perceptual deficits including object recognition impairments (Barton et al., 2004 and Clarke et al., 1997), but in general, prosopagnosic patients do not have difficulty discriminating faces from objects (Damasio et al., 1982, Orban de Xivry et al., 2008 and Rossion et al., 2003). For normal perception of faces, the face features are combined into a single configuration, not treated as separate units (Sergent & Signoret, 1992b). This holistic encoding of facial structures is lost in prosopagnosia (Bodamer, 1947, Ellis and Florence, 1990 and Van Belle et al., 2010). The purpose of the current studies was to use IATs to determine whether a patient, despite an inability to overtly recognize familiar faces, could elicit implicit biases about the race, gender, political views, or likability of the person shown, and consequently display an IAT effect due to that bias. To our knowledge, no patient with prosopagnosia has been tested on IATs that use faces. We also tested the patient on his ability to categorize faces explicitly by race and gender, to recognize faces overtly, and to determine if he was faster to respond to faces already seen. Covert face recognition has been demonstrated in prosopagnosia. As this recognition process is not consciously accessible, investigators must use methods other than verbal report to uncover it. Bruyer et al. (1983) report on a patient who made few errors when learning to associate true first names to famous faces, but made many errors when learning to associate incorrect first names to famous faces, even though the patient could not overtly identify the faces. Bauer (1984) found that during tasks of matching names to known faces, a prosopagnosic patient's skin conductance responses (SCR) were three times more accurate in matching the correct name to a face than was the patient's explicit choice. Similarly, Tranel and Damasio, 1985 and Tranel and Damasio, 1988 displayed known and unknown faces to six patients who could not overtly recognize the faces but showed larger amplitude SCRs to the known compared to unknown faces. Jones and Tranel (2001) found normal SCRs to pictures of immediate family and close friends in a child with prosopagnosia. Rizzo, Hurtig, and Damasio (1987) found that prosopagnosic patients scanned photographs of familiar faces in different patterns than unfamiliar faces. Also, reaction times for prosopagnosic patients in a name classification task were longer when a distractor rather than a matching face was shown (de Haan et al., 1992 and de Haan et al., 1987b). Similarly, Young, Hellawell, and De Haan (1988) demonstrated that related face primes shortened patients’ mean RTs when judging familiarity of printed names while unrelated face primes lengthened mean RTs. Also, a patient was systematically faster to react to familiar compared to unfamiliar faces while deciding whether two photographs showed the same or different faces (de Haan, Young, & Newcombe, 1987a). These instances of covert recognition in prosopagnosics have been interpreted as indicating that subcomponents of the physiological process of face categorization remain intact even though they are not available to patients’ consciousness (Sergent and Poncet, 1990 and Tranel, 2000). 1.1. Implicit Association Tests Attitudes have been explored extensively using IATs (Greenwald et al., 1998 and Greenwald and Nosek, 2001). In an IAT, participants are presented two tasks: one requires categorization of images into one of two categories (e.g., white or black faces); the other requires categorization of words into one of two attributes (e.g., pleasant or unpleasant). The two response keys are mapped in either a congruent or incongruent manner according to conventional stereotypes (white = pleasant, black = unpleasant). The typical finding is that participants respond faster to stereotype-congruent than to stereotype-incongruent trials. In this way, reaction times can be used to gauge the strength of association between stimuli and the participant's implicit attitudes. 1.2. Case report The patient, G.B., is a Caucasian male who was born in Egypt and immigrated to the U.S. at age 9 with his family. His first language was French but his primary language is English. He also speaks Spanish. He has 20 years of education, was employed pre-injury as a physician, and since his injury has worked in several medical offices, at both paid and volunteer positions. In 2003, he sustained bilateral temporal lobe lesions, including fusiform gyri, and diffuse axonal injury due to an auto-pedestrian collision. He was diagnosed with prosopagnosia and difficulties with stimulus salience, with some object agnosia and left sensory hemi-inattention. MRI results three years post-injury showed a few nonspecific small patchy foci of hyperintense signal in the supratentorial white matter for the T2 and Flair sequences. In addition, there were two large areas of encephalomalacia with volume loss inferior to the temporal horns (posterior temporal areas extending into parieto-occipital cortex including fusiform gyrus), and a small area of encephalomalacia in the right anterior temporal lobe. His brain injury is consistent with descriptions of brain damage in acquired prosopagnosia (Barton, 2008b, Barton et al., 2004, Damasio et al., 1982, Grafman et al., 1986 and Takahashi et al., 1995). See Fig. 1.

Conclusions We have shown for the first time that the IAT effect can be added to the list of covert recognition effects found in prosopagnosia (Bobes et al., 2003, Schweinberger and Burton, 2003, Tranel, 2000 and Tranel et al., 1995). In some of the IATs, G.B. demonstrated the ability to perform covert recognition of faces without overt awareness of explicit information such as the name of the person or the category to which he or she belongs. Some of the attitudes went above and beyond stereotypes based on surface feature extraction such as skin color in the race IAT, but were based on knowledge of the person such as likability in the celebrity IAT. While G.B. did not have an IAT effect in each IAT, he did in two of the four, demonstrating that it is possible for a patient with prosopagnosia to show covert recognition of faces. We encourage further study of prosopagnosia using IATs on other patients. Acknowledgements We thank G.B. for his participation, Joshua Poore for his comments on an earlier manuscript, Tianxia Wu for her statistical guidance, and the anonymous reviewers for their insightful comments. This study was supported by the Intramural Research Program of the National Institute of Neurological Disorders and Stroke, National Institutes of Health. The authors declare no conflict of interest. Some of the faces were obtained from the MacBrain Face Stimulus Set. Development of the MacBrain Face Stimulus Set was overseen by Nim Tottenham and supported by the John D. and Catherine T. MacArthur Foundation Research Network on Early Experience and Brain Development. Please contact Nim Tottenham at tott0006@tc.umn.edu for more information concerning the stimulus set. The Caltech Frontal face dataset (Faces 1999) was collected by Markus Weber at the California Institute of Technology and can be obtained at http://www.vision.caltech.edu/html-files/archive.html.