Asymmetrical face perception with in-depth rotated faces
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Asymmetrical face perception with in−depth rotated faces ¨ A.I. Ruppertsberg, T. Vetter and H.H. Bulthoff TWK 99 ¨ ¨ Max−Planck−Institut fur biologische Kybernetik Tubingen http://www.kyb.tuebingen.mpg.de/bu.html 1 INTRODUCTION 2 METHODS Burt &Perrett (1997) showed that subject’s judgment of gender, age and expression were more influenced by the Training Testing left than by the right side of the face (viewer’s In the learning stage, In a delayed−match−to−sample task subjects were presented perspective). Also in similarity studies it was shown that a left composite face was rated as more similiar to the subjects were asked a frontal view of a face for 100 ms, followed by a mask for original than a right composite face (Gilbert et al., 1973, to study 10 frontal 500 ms, and finally a side view (+/− 30 and 60 deg) of a face views of ANA TIM EVA ISA SAM for again 100 ms. Rhodes, 1985). 3D−Cyberware head Is this asymmetry an asymmetry in perception or in same scans with their or coding? respective names for different person ten minutes. MIA UTA OLI EDI ALI ? We investigated whether recognition performance differs for faces rotated in depth to the right or to the left. 600 100 500 500 100 Immediately after they were tested in a naming task, where a Time [ms] face was shown on the computer screen and subjects had to press the corresponding name key on the keyboard. When The task was to assess whether the two views depicted the Note: Left and right are used here always from the their error rate was lower than 5% over the last 30 trials they same person or not. viewer’s perspective. continued with the actual experiment. At that stage they had Subjects were asked to respond as fast as possible and their named each face at least three times. response time and errors were recorded. 3 RESULTS Experiment 1 Normal Faces Experiment 2 Symmetrical Faces Q: Is there a difference in performance Factors: Familiarity Orientation Q: Is the asymmetrical performance Factors: Familiarity Orientation between left and right in depth rotated Levels: familiar −60 deg due to the slight asymmetry in the Levels: familiar −60 deg unfamiliar −30 deg unfamiliar −30 deg faces? +30 deg face? +30 deg +60 deg −>We made all faces symmetrical. +60 deg N = 15 N = 17 17 Subjects 25 Normal Faces 8 familiar 20 unfamiliar 6 Error difference [%] 5 Subjects make more 4 * errors the further the 15 For symmetrical faces subjects’ Errors [%] Error difference 2 face is rotated away from performance show different results for 00 10 the frontal view. familiar and unfamiliar faces. −2 Error difference [%] −4 5 −x deg +x deg −5−6 0 For familiar faces subjects show the −60 −30 30 60 15 Subjects −8 60 30 Subjects make more Orientation angle [deg] same behavior as for normal faces: they 25 60 30 errors when the face is Symmetrical Faces make more errors when the face is 20 turned to the left side. rotated to the left. Error difference [%] 55 unfamiliar * 15 00 Errors [%] E(−x deg) − E(+x deg) −5 −5 For unfamiliar faces the behavior is 10 60 60 30 30 reversed to the contrary: Subjects make < 0 more errors to the right more errors when the unfamiliar 55 familiar 5 > 0 more errors to the left symmetrical face is turned to the right. 00 0 −60 −30 30 60 −5 −5 * Orientation angle [deg] 60 30 60 30 3 RESULTS 4 CONCLUSIONS From Experiment 1 we conclude, that there is indeed a difference Experiment 3 Visual Field in our ability to recognize a person depending on the side of the face we see. In accordance with Burt and Perrett’s results that perception of faces is biased to the left side of a face our results Q: Is the effect due to the location of Factors: Group Familiarity Visual Field Orientation show that people make more errors when they cannot see the left Levels: Set 1 familiar central −60 deg presentation in the visual field? Set 2 unfamiliar left −30 deg side of the face (−x deg rotation). right +30 deg −>The rotated face is presented in +60 deg N = 18 From Experiment 2 we conclude, that the asymmetry per se in a the left, right, or central visual field (+/− 2.6 face is not the origin of the asymmetrical performance but rather deg). that the analysis of familiar and unfamiliar faces differs. There was no effect of the set Q: Is the selection of faces biased? of faces used. From Experiment 3 we conclude that the right hemisphere is the −>Two groups of subjects learned a specialized face processing hemisphere since presentation of When faces are presented in different set of ten familar faces. faces in the left visual field results in the same behavior as the central visual field, presentation of faces in the central visual field. subjects make less errors than when they are presented in Subjects make more errors for right rotated faces when they are the left or the right visual field either unfamiliar or presented in the right visual field. All Faces, 18 Subjects and there is a tendency that left VF central VF right VF 30 8 8 8 presentation in the right visual It is still not clear whethera symmertrical object is coded left VF 6 6 6 field leads to a lower asymmetrically. 25 central VF right VF 4 * 4 4 * performance than a Since the effect in general is quite small can we get more 20 presentation in the left visual Error difference 2 2 2 significant results for the observed asymmetries with more Errors [%] field. 15 0 0 0 subjects? −2 −2 −2 Subjects make more errors for 10 Is there a difference in the task for familiar and unfamiliar faces −4 −4 −4 left rotated faces when they because the coding of the faces is different? 5 −6 −6 −6 are shown in the central and 0 left visual field. −8 −8 −8 −60 −30 30 Orientation angle [deg] 60 60 30 60 30 60 30 In the right visual field however subjects make more References: errors for right rotated faces. Burt, D. M. and Perrett, D. I., 1997, Neuropsychologia 35, 685−693. Rhodes, G.,1985, Brain and Cognition 4, 197−218. Gilbert, C. and Bakan, P., 1973, Neuropsychologia 11, 355−362.