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Self-face identification is increased with left hand responses

Self-face identification is increased with left hand responses
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  Self-face identification is increased withleft hand responses Julian Paul Keenan  Harvard Medical School, USA Giorgio Ganis  Harvard Medical School and Harvard University, USA Stefanie Freund and Alvaro Pascual-Leone  Harvard Medical School, USA Evidence suggests that autobiographical memory, self-related semantic category judgements, and self-identification tasks may be lateralised, with preferentialactivityinthe right anterior temporal and prefrontalcortex. To test thishypothesis,participants (N=10) were presented with morphed images of themselves (self)combined with a famous face. A further set of images was generated in whichtheface of one of the participant’s co-workers (familiar)wascombined witha famousface. When compared to morphed images composed of a familiar face, theparticipants identified images less often as being famous if the images werecomposed of self, but only when responding with their left hands. This greater‘‘self-effect’’ found in left-hand responses may imply that when the righthemisphere is preferentiallyactive, participants have a tendency to refer images toself. These data provide further support for a preferential role of the righthemisphere in processing self-related material. Agrowingnumber of studies implicate the right temporal andprefrontal corticesin the processing of various aspects of self-related information and material (e.g.Wheeler, Stuss, &Tulving, 1997). Activityin the right hemisphere appearsto becorrelated with processing of material related to one’s own body in space(Demaree & Harrison, 1997; Mesulam, 1981; Pimental & Kingsbury, 1989; LATERALITY, 2000,  5  (3), 259–268Correspondence should be sent to Julian Paul Keenan PhD, Laboratory for Magnetic BrainStimulation, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215, USA.Email: jkeenan@caregroup.harvard.eduSupported in part by grants from the NIMH, NEI, NARSAD, and the Stanley Vada NAMIFoundation. This work was completed in part for the requirements of the dissertation at theUniversityat Albany forJPK. Wewish tothank Roy Hamilton forhishelp with the overall designof the experiment. The two anonymous reviewers are also thanked for their insightful comments. Ó 2000 Psychology Press Ltd  Springer & Deutsch, 1985). More recent evidence has suggested that bothmental state attribution (Baron-Cohen et al., 1994; Happe, Brownell, &Winner,1999) and cognitive self-representation (e.g., Stuss &Benson, 1986) engage theright prefrontal cortex preferentially. For example, Fink et al. (1996), usingpositron emission tomography (PET), found that when participants werepresented with sentences containing autobiographical information, there was anincrease in right prefrontal cerebral blood flow when compared to ‘‘autobio-graphical’’ information of another person. In a series of single photon emissioncomputerised tomography (SPECT) and magnetic resonance imaging (MRI)scans, Calabrese et al. (1996) found functional and anatomical damage to theright temporal-frontal region when he examined a patient afflicted with herpessimplex type I encephalitis who was unable to recall older episodic memories.Markowitsch et al. (1997) tested a patient who had episodic amnesia usingSPECT and found decreased blood flow in the right frontal and temporal areas,in the absence of any obvious anatomical damage. Other neuroimaging studiestesting self-related (episodic) retrieval in normals have also indicated that self-related memoryis correlatedwith activity in the right frontal lobes (see Wheeleret al., 1997). Recently Craik et al. (1999), employing PET presented subjectswith an adjective list and asked them in one condition to decide if the wordsdescribed themselves, and in the other condition, to decide if the wordsdescribed a famous person. Greater cerebral blood flow was found in the rightprefrontal cortex during the condition in which subjects were making self-related judgements as compared to the other conditions.The role of the right temporo-frontal and prefrontal cortex in processing self-related material does not seem restricted to episodic memory or internallygenerated information (as in Craik et al., 1999). Our own previous studiessuggest a critical role of the right prefrontal cortex in processing visual imagesof one’s own face. In a choice reaction time paradigm, where participantsviewed pictures of their own face, familiar people’s faces, or strangers’ facesand responded with their right or left hand, the reaction times were significantlyshorter for left-hand responses to self pictures than for any other condition(Keenan et al., 1999). Further, using repetitive transcranial magnetic stimulation(rTMS) to transiently disrupt the function of the targeted cortical region (e.g.Kosslyn et al., 1999, Pascual-Leone, Bartres-Faz, & Keenan, 1999), reactiontimes were altered for self-faces only after right prefrontal stimulation (Keenan,Hamilton, Freund, & Pascual-Leone, 1999). These experiments, however, werebased solely on recognition of one’s own face compared with other faces, andonly speed and accuracy of identification were measured.Toextend these previous results, wemanipulated self-facesto create a task inwhich thresholds for self and familiar detection could be measured. Wecombined images of the faces of famous people with the faces of participantsand their co-workers. A series of images (morphs) were created in which thepercentage of the famous face was gradually increased. Out of these stimuli, we 260  KEENAN ET AL.  developed an identification paradigm in which the subjects were asked to notewhich faces were famous. Employing this method we were able to determinethreshold differences (i.e., the amount of self or familiar needed to identify ornot identify a face as famous) between hand used to respondand composition of the morphs. It was predicted that when participants used their left hand torespond, they would be less likely to identify self-morphs as being the face of afamous person. METHODParticipants A total of 10 normal volunteers, 6 men and 4 women, ages 19 to 36 (M=25.2,SD=6.4) were studied. The study was approved by the local InstitutionalReview Board and written informed consent was obtained from all participants.All participants were right-handed as determined by the Edinburgh ques-tionnaire (Oldfield, 1971). All were healthy and had normal neurological andphysical exams. Participants were matched with a co-worker of the same genderwith whomthey had worked for the previous year. These pairs werenoted as theparticipant (self) and his/her co-worker (familiar). Materials Prior to the experiment, photographs were obtained from each of theparticipants. All images were photographed on a PC/Mac Kodak DC-50 digitalcamera on mid-1.5 zoom at high resolution (756 6 504) at a distance of 70cm.All photographstaken werebacklit and the participants wereinstructed to keepaneutral expression during image acquisition. The photographs wereprocessedinPaint Shop Pro v. 3.0 (JASC Inc, Eden Prairie, MN) and were first cropped sothat the bottomof the image beganat the chin, and the top of the image ended atthe top of the hair. The black and white images were stretched into a standardspace (320 6 200 pixels).The morphing normalisation wasachieved by combining one of these imageswith one of four images of faces of famous people. This process was achievedusing Morph Editor (SoftKeyCorporation, Cambridge, MA). The programtakestwo images and starts at X, Ypoint 0, 0. The user then defines the percentage of image 1 to overlay on to image 2. If 25% is defined, the computer will beginalong the X-axis and replace every fourth pixel of image 2 with image 1. Thisprocess continues throughout the entire image.To create a series of morphed images, 30–60 anatomical landmarks fromeach face were aligned manually (points on nose, hair and hairline, mouth etc.).For example, the tip of the nose of Participant 1 was defined, and then the tip of the nose of Bill Clinton was defined. This process continued until a smoothmorph (at 50%) was generated. This process was carried out for each participant LATERALITY AND RESPONSES TO SELF-FACES  261  (i.e., each male participant was morphed into Bill Clinton and Albert Einstein,and each female participant was morphed into Marilyn Monroe and PrincessDiana, see Figure 1).The morphed images were categorised according to percent pixel replace-ment. For simplicity, the notation is given in ‘‘percent famous person’’: Amorph between self and famous at 65% would describe a picture that was 65%Albert Einstein and 35% the participant. A total of 20 images, per participant,per famous person were created. Therefore, each participant had a total of 40images (e.g., 20 self–Bill Clinton and 20 self–Albert Einstein images) and eachstep reflected a gradation of 5% (from 5% famous to 100% famous). Experimental design Participants were instructed to respond using a computer keyboard as quickly aspossible with an identification of the images that appeared on the screen. Allparticipants were tested on a PC running SuperLab v 1.71 (Cedrus Corporation,Phoenix, AZ). Participants sat 18 inches from the computer screen held at eyelevel and used either the right or left hand to respond. The order of theexperiments were counterbalanced across participants.Each participant completed a total of 960 trials (480 self, 480 familiar). Totaltesting time was approximately 15 minutes. The 480 responses were made up of 240 right-hand and 240 left-hand responses. The 240 responses for each handand stimulus condition were made up of 6 presentations of 2 famous morphseries (2 famous faces 6 20 morph levels 6 6 repetitions). The participantswere instructed to press one key if they thought an image was ‘‘more famousthan not’’ (e.g. ‘‘press the ‘C’ key if you think the picture is more Bill Clintonthan not Bill Clinton’’). They were to press a different key (‘‘Z’’) if they didnot think the image was ‘‘more famous than not’’. For half of the participantsthe meaning assigned of the two response keys (‘‘C’’ and ‘‘Z’’) was inverted.The keyboard was centred to the response hand used. Response times weremeasured as the time it took from the onset of image display to the responsekey press.The number of identifications for each level was tabulated. For example, aparticipant mayhave givenfour positive identifications (indicating, this image ismore Marilyn Monroe than not Marilyn Monroe) insix attempts whenthe imagewas 80% famous. Therefore, this participant would have given a 66% positiveidentification rate at the 80% level. Overall identification rates were calculatedby averaging the number of positive identifications across all levels (the averagepercentage of positive responses across  all  morph levels).Data were analysed using Statistical Packages for Social Sciences (SPSSv9.0) (SPSS Inc., Chicago IL, USA). The number of identifications wascompared at each morph level, as well as across all morph levels. Responsetimes were also compared across and within each morph level. Analysis of data 262  KEENAN ET AL.  Figure 1.  The morphingprocess. The participant’simage is combined with afamous face to create aseries of 20 morphedimages. Each steprepresents a change of 5%,starting with 5% of theimage being composed of afamous person, ending withan image being composedof 100%. These imageswere randomly displayed toeach of the participants. 2   6   3  
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