What s special about personally familiar faces? A multimodal approach

Transcription

1 Psychophysiology, 41 (2004), Blackwell Publishing Inc. Printed in the USA. Copyright r 2004 Society for Psychophysiological Research DOI: /j x What s special about personally familiar faces? A multimodal approach GRIT HERZMANN, a STEFAN R. SCHWEINBERGER, b WERNER SOMMER, a and INES JENTZSCH c a Department of Psychology, Humboldt-University at Berlin, Berlin, Germany b Department of Psychology,University of Glasgow, Glasgow, UK c School of Psychology,University of St. Andrews, St. Andrews, UK Abstract Dual-route models of face recognition suggest separate cognitive and affective routes. The predictions of these models were assessed in recognition tasks with unfamiliar, famous, and personally familiar faces. Whereas larger autonomic responses were only triggered for personally familiar faces, priming effects in reaction times to these faces, presumably reflecting cognitive recognition processes, were equal to those of famous faces. Activation of stored structural representations of familiar faces (face recognition units) was assessed by recording the N250r component in event-related brain potentials. Face recognition unit activation increased from unfamiliar over famous to personally familiar faces, suggesting that there are stronger representations for personally familiar than for famous faces. Because the topographies of the N250r for personally and famous faces were indistinguishable, a similar network of face recognition units can be assumed for both types of faces. Descriptors: Face recognition models, Skin conductance responses, Event-related brain potentials, Priming, Personally known faces Human faces are outstandingly rich sources of information for social interaction, providing detailed information about familiarity, identity, mood, gender, age, or focus of attention. It is therefore hardly surprising that the issues of how the cognitive system accomplishes and how the brain implements these aspects of face perception have enjoyed a great deal of scientific interest. Traditional models of face recognition (Bruce & Young, 1986; Hay & Young, 1982) have focused mainly on cognitive processes. However, more recent models (Breen, Caine, & Coltheart, 2000; Ellis & Lewis, 2001) have included affective aspects of face recognition as well. These models suggest that a so-called cognitive route analyzes the identity of faces and provides access to semantic knowledge and name of familiar persons. In addition, a second route is thought to be involved in the production of affective responses to familiar faces. The assumption of these distinct routes in face processing was made in order to explain This research was supported by a Socrates-Erasmus exchange studentship to G.H. while she was visiting Glasgow, by a grant by the Deutsche Forschungsgemeinschaft (So 177/14-1) to W.S., and by grants by the Biotechnology and Biological Sciences Research Council (17/ S14233) and the Royal Society to S.R.S. Address reprint requests to: Grit Herzmann, Department of Psychology, Humboldt-University at Berlin, Rudower Chaussee 18, D Berlin, Germany. grit.herzmann@cms.hu-berlin.de, or to Stefan R. Schweinberger, Department of Psychology, University of Glasgow, Glasgow G12 8QQ, Scotland. s.schweinberger@psy. gla.ac.uk. impairments of face recognition in prosopagnosia and its supposed counterpart, Capgras delusion. Patients with prosopagnosia are unable to identify the faces of familiar persons and to learn new faces. Typically, prosopagnosia is a consequence of acquired brain damage, involving inferior occipito-temporal lesions of the right or both hemispheres. These patients often remain able to recognize familiar persons by voice or gait, and may also show preserved semantic memory for people, for example, when confronted with their names. Nevertheless, prosopagnosic patients may be unable to recognize faces of even highly familiar people. However, such faces, even though overtly unrecognized, may elicit signs of covert recognition, such as skin conductance responses (SCR). For example, Bauer (1984) presented the prosopagnosic patient LF with familiar faces, paired with spoken names, which could or could not correspond to the face. Although LF could not identify the correct names, his SCRs were larger to correct than incorrect face/name pairs. In other studies, prosopagnosic patients showed larger SCRs to familiar as compared to unfamiliar faces in the absence of overt recognition (Tranel & Damasio, 1985). In terms of dualroute models, preserved differential SCRs may indicate that some patients with prosopagnosia, although impaired in overt recognition along the cognitive route of face recognition, still have a relatively intact affective route. Patients with Capgras delusion show a pattern of impairment that appears to be almost the mirror image of prosopagnosia (Ellis & Young, 1990). Capgras delusion may occur in the context 688

2 What s special about personally familiar faces? 689 of psychiatric conditions or as a result of structural or toxic brain damage. Although these patients are still able to identify familiar faces, they lack a sense of familiarity to these faces and believe that impostors, doubles, or aliens have replaced these people (e.g., spouses or children). Ellis and Young proposed that Capgras patients, though unimpaired in their cognitive route for face recognition, might have a damaged affective route. Their prediction that these patients would fail to produce a differential SCR response to overtly recognized familiar faces was confirmed by subsequent research (Ellis, Young, Quayle, & DePauw, 1997; Hirstein & Ramachandran, 1997). The dissociation of autonomic responses and overt face recognition in prosopagnosia and Capgras delusion was taken as support for the existence of two routes to face recognition. Bauer (1984) postulated two routes for face recognition in both neuroanatomical and functional terms. A ventral visual-limbic route in inferior temporal cortex was suggested to mediate overt identification and to be impaired in prosopagnosia. A dorsal route projecting from primary visual cortex to limbic structures via the superior temporal sulcus and inferior parietal lobe was considered to be involved in the detection of emotional significance and to mediate the preserved SCR responses in prosopagnosic patients. Ellis and Young (1990) adopted Bauer s dual-route model to accommodate Capgras delusion, which was considered to be the consequence of damage in the affective route, as indicated by the absence of SCRs to familiar faces (Ellis et al., 1997). The theories of both Bauer (1984) and Ellis and Young (1990) claim that a face has to be identified to some degree before its relevance for affective responses can be noticed. In terms of current concepts about face recognition (e.g., Bruce & Young, 1986) these models therefore make the implicit assumption of two independent sets of stored representations of familiar faces (face recognition units) feeding into the affective and the cognitive routes. Recently, Breen et al. (2000) pointed out that Bauer s model does not specify possible mechanisms for face recognition in the dorsal route and noted that there is little evidence for object or face recognition in this route (Ungerleider & Mishkin, 1982). Therefore, Breen et al. made the more parsimonious suggestion of one common pool of FRUs residing within the ventral visual stream and feeding into both the cognitive and affective routes. Breen et al. adapted the face recognition model of Bruce and Young, which contains only a singlefcognitivefroute, by adding a module triggering affective responses to familiar faces. In the modified model, face recognition units feed information simultaneously and independently into both person identity nodes and the affective module. Face recognition is thought to take place along an anatomical route in ventral temporal lobe structures, with the amygdala triggering affective responses to familiar faces. Within this framework, Breen et al. explained the dissociation between patients with prosopagnosia and Capgras delusion. Prosopagnosia can be caused by an impaired connection between the face recognition units and the person identity nodes, while the connection between the face recognition units and the affective response module may be intact. In contrast, the locus of impairment in Capgras delusion is either within the affective module or in the connection between the face recognition units and the affective module (see Figure 1). Subsequently, Ellis and Lewis (2001) slightly modified the dual-route model of Breen et al. by adding an integrative device, which compares the outputs of the affective and cognitive routes. This was done to explain the delusion in Capgras patients when a familiar face fails to elicit a corresponding affective response. Taken together, all models of face recognition that attempt to encompass both findings in prosopagnosia and Capgras delusion and differences between overt and covert face recognition (Bauer, 1984; Breen et al., 2000; Ellis & Lewis, 2001; Ellis & Young, 1990; Ellis et al., 1997) include two routes to face recognition, termed affective and cognitive. As a result, dual-route models provide a comprehensive framework for assumptions and investigations of face recognition. For intact processing systems, the models postulate a similar relationship between facial familiarity and response strength. For example, Breen et al. predict that the affective response should increase with the degree of familiarity. PreviousFmainly neuropsychologicalfresearch, which included only one or two types of facial familiarity, confirmed this relationship in the affective route. SCRs were more pronounced for famous than for unfamiliar persons (Tranel & Damasio, 1985; Tranel, Fowles, & Damasio, 1985) or for personally familiar than for famous faces (Tranel, Damasio, & Damasio, 1995). From these observations and in line with dual-route models one would expect SCRs to increase with facial familiarity when unfamiliar, famous, and personally familiar faces are compared. Similarly, it can be thought that face familiarity should improve cognitive processing. This has been demonstrated for the comparison of famous with unfamiliar faces in several suggested probes of processing within the cognitive route: priming, interference, matching effects, and the speed of face-name learning (Bruce & Young 1986; Ellis, Lewis, Moselhy, & Young, 2000; Pfütze, Sommer, & Schweinberger, 2002). Repetition priming for faces reflects facilitation, for example, in reaction times to a face that has been processed before, relative to initial encounter (Bruce & Young, 1986). Current models of face recognition (Burton, Bruce, & Hancock, 1999) assume that the decision about facial familiarity is made at the person identity node level. Whereas long-term repetition priming is thought to be mediated mainly by the strengthening of links between face recognition units and person identity nodes, immediate repetition priming appears to involve facilitation at an earlier level of access to face recognition units and/or structural encoding (Pfütze et al., 2002; Schweinberger, Pfu tze, & Sommer, 1995; Schweinberger, Pickering, Jentzsch, Burton, & Kaufmann, 2002). Therefore, repetition priming in face identification may involve facilitation at several loci along the cognitive route. Whereas previous studies revealed stronger priming effects in RTs for famous than for unfamiliar faces (Bruce & Valentine, 1985; Ellis et al., 2000; Pfütze et al., 2002), personally familiar faces do not seem to have been studied for priming effects. It is therefore an open question whether there would also be an increase from famous to personally familiar faces in RT priming. Importantly, current research, mainly based on the model of face recognition by Bruce and Young (1986), has identified at least two consistent ERP correlates of face recognition within a repetition priming task paradigm. First, a negativity for primed relative to unprimed faces is seen over inferior temporal electrodes at latencies of around ms, an effect that has been variously termed N250r or early repetition effect (ERE; Pfütze et al., 2002; Schweinberger et al., 1995; Schweinberger, Pickering, Jentzsch, et al., 2002). The N250r is typically larger over the right than left hemisphere and is not present for associative-semantic priming (Schweinberger, 1996). Moreover, the N250r is reduced or even absent for unfamiliar as compared to famous faces (Pfütze et al., 2002; Schweinberger et al., 1995), suggesting that it depends on the contact with an existing memory representation. Although an N250r at similar latency as for

3 690 G. Herzmann et al. Figure 1. An adaptation of the dual-route models of face recognition proposed by Breen et al. (2000) and Ellis and Lewis (2001). Face recognition is considered as matching a seen face to its stored representation at the level of the face recognition units. Face recognition units activate simultaneously but independently the affective and the cognitive routes. The affective route leads to a module triggering affective responses to familiar stimuli, of which skin conductance response is an indicator. The cognitive route leads to person identity nodes, activates semantic information, and supports name retrieval. An abnormality at location A will cause a loss of overt face recognition and is therefore a possible explanation for prosopagnosia. An abnormality at location B will cause a loss of differential SCR responses to familiar and unfamiliar stimuli. It will also cause a discrepancy in the integrative device and is therefore a possible account for Capgras delusion. In the context of the present study, SCR responses are thought to be mainly sensitive to activity along the affective route (B), RTpriming effects are thought to be mainly sensitive to activity along the cognitive route (A), and the ERE should be sensitive to activity in the face recognition units. faces has been observed for written names, this effect is maximal over the left hemisphere (Pfütze et al., 2002; Pickering & Schweinberger, 2003). Thus, the N250r has a stimulus-dependent topography, suggesting that it links to perceptual rather than postperceptual representations. The face-elicited N250r has been related to the transient activation of face recognition units, and is therefore also of particular interest for dual-route models. Another consistent ERP correlate of face priming is a late ERP repetition effect (N400 or LRE), an increased centroparietal positivity (or reduced negativity) for repeated faces at latencies around ms (Bentin & McCarthy, 1994; Schweinberger et al., 1995; Schweinberger, Pickering, Burton, & Kaufmann, 2002). This late repetition effect is likely related to the N400, which was initially demonstrated to reflect the detection of semantic incongruency in sentences and was thought to represent semantic integration (Kutas & Hillyard, 1980). An N400-like pattern can also be elicited by faces, when these are preceded by the same or by associated faces. The N400 may reflect facilitation in assessing postperceptual or semantic memory codes for people (person identity node). According to assumptions about cognitive networks for face recognition (Burton et al., 1999; Mohr, Landgrebe, & Schweinberger, 2002), priming should especially facilitate recognition of those faces for which there are stronger memory representations. To the extent that a more frequent encounter of personally familiar as compared to famous faces might have induced stronger neurocognitive networks, it might be expected that the N250r increases from famous faces to personally familiar ones. Importantly, the different versions of dual-route models disagree with respect to the locus at which the two routes diverge. Some models state that both routes diverge early in processing and therefore imply two distinct sets of recognition mechanisms, or face recognition units (Bauer, 1984; Ellis et al., 1997; Hirstein & Ramachandran, 1997). Other models explicitly assert a common face recognition unit with the two routes diverging only subsequently (Breen et al., 2000; Ellis & Lewis, 2001). The N250r can provide functional evidence about face processing, and the scalp topography of this component can, to some extent, provide information about underlying sources. If the N250r for two different types of facial familiarity showed different scalp topographies, this would be evidence for the involvement of at least partially different neural generators. To the extent that N250r to personally familiar faces reflect the activation of a different set of face recognition units as compared to famous faces, for example in a dorsal affective route (Bauer, 1984; Ellis et al., 1997; Hirstein & Ramachandran, 1997), it

4 What s special about personally familiar faces? 691 should be reflected in distinguishable topographies of the N250r to famous and personally familiar faces. In contrast, if affective and cognitive routes of face recognition diverge only after the access to a common pools of face recognition units (Breen et al., 2000; Ellis & Lewis, 2001), the N250r topographies should not differ. To our knowledge, the postulations of dual-route models for both affective and cognitive aspects have not yet been tested for more than two types of facial familiarity in the same healthy population. For that reason it was the first objective of the present study to provide a more comprehensive test of the predictions of dual-route models. We assessed several indices for affective and cognitive aspects of face recognition, as a function of different types of facial familiarity. More specifically, we investigated in healthy participants how unfamiliar, famous, and personally familiar faces are processed at several levels of the face recognition system. The affective route was assessed by recording skin conductance responses, the cognitive route was investigated with a short-term repetition priming task, and the N250r provided a tool to investigate the effects of facial familiarity on the face recognition units. Addressing the question of separate or common face recognition units was the second objective of the present study. To answer this question we also used the N250r. Because of the different methodological requirements for recording SCRs and ERPs, the experiment was divided into two parts where the same stimuli and the same participants were employed. In Part 1 of the experiment, we explored the influence of different types of facial familiarity on the affective route by examining modulations in SCRs. In the second part of the experiment, we investigated effects on the cognitive route as seen in RT priming effects. EXPERIMENT: PART 1FSCR In Part 1 of the experiment we investigated the affective aspects in face recognition by means of recording SCRs as a function of facial familiarity. Method Participants Twenty-four participants (21 women, 3 men) with ages ranging from 19 to 33 years (M years, SD 5 3.2) were paid to contribute data to the experiment. According to an adapted version of the Edinburgh Handedness Inventory (Oldfield, 1971) participants were strongly right-handed (M , range ). They reported normal or corrected-to-normal visual acuity. All participants were psychology students at the University of Glasgow, and had been residents of the United Kingdom or Ireland for a minimum of 5 years. Stimuli Sixty portraits were used, consisting of 15 personally familiar, 15 famous, and 30 unfamiliar faces. Photographs of famous and unfamiliar persons were made available from earlier research. The celebrities had been selected on the basis of previous high ratings for ease of face recognition (Schweinberger, Pickering, Burton, et al., 2002). Portraits of personally familiar persons were taken from the lecturing staff in the Department of Psychology at the University of Glasgow. All portraits were edited to a unitary format. They were converted to gray scale, framed within an area of pixels, corresponding to cm, and all background was removed. An attempt was made to homogenize the pictures with respect to contrast and average luminance across the sets of famous, personally familiar, and unfamiliar faces. Prior to the experiment, the 15 best known personally familiar persons and 15 best known celebrities were selected for each participant out of two pools of pictures of 15 men and 7 women each. To avoid any priming or habituation for the face stimuli, these selections were based on the person s names. Each person was rated for ease of possible face recognition on a 5-point scale. The selected unfamiliar faces were matched to familiar counterparts with respect to gender, approximate age, general portrait style, and expression. Procedure After the rating participants were seated in a dimly lit, soundattenuated, and electrically shielded chamber. A fixed chin rest was used to maintain a constant viewing distance of 1 m. A white fixation cross in the center of the monitor changed into bold font 5 s before the onset of a face. The 60 faces were presented once for 2,000 ms in randomized order with interstimulus intervals between 12 and 18 s. The familiarity of each face was indicated by key presses with the index and middle finger of the right hand. Half the participants pressed the left key (index finger) for a familiar face and the right key (middle finger) for an unfamiliar face; this assignment of key to response category was reversed for the other half. Responses were scored as correct if the appropriate key was pressed within a time window of 200 to 2,000 ms after face onset. Errors of omission (no key press) and commission (wrong key) were recorded separately. Mean RTs were calculated for correct responses only. The experiment started with three practice trials, to be discarded later. After completion of both parts of the experiment participants rated the portraits shown, using the same rating scale as in the beginning. As expected, the face sets differed, with both personally familiar and famous faces being both rated as well known (M and 3.9, respectively), and unfamiliar faces as unknown (M 5 0.2). Recording For SCR measurement, sintered Beckman Ag/AgCl electrodes, 1 cm in diameter, were affixed to the thenar and hypothenar eminences of the left hand; a ground electrode was placed at the left forearm. Isotonic electrolyte gel (K-Y Jelly, Johnson 1 Johnsont) was used. Skin conductance was recorded with a Coulbournt Isolated Skin Conductance Coupler (Model V71-23), and digitized at a sampling rate of 200 Hz. Off-line, 10-s epochs, starting 1 s before stimulus onset, were analyzed. A total of 2.1% of all trials were excluded from analysis because of artefacts. In addition to RTs and error rates, several response parameters were derived from the SCR (see below). Results were evaluated by means of Huynh Feldt (Huynh & Feldt, 1976) corrected repeated-measures ANOVAs; pairwise comparisons between levels of familiarity were Bonferroni corrected. Withinsubject repeated measures are reported with (a) uncorrected degrees of freedom, (b) the corrected p value, and (c) the epsilon value of the correction factor.

5 692 G. Herzmann et al. Results and Discussion Performance Means and standard deviations of RTs and error rates are shown in Table 1. In RTs, a significant main effect of familiarity was observed, F(2,46) , po.001, e Responses to unfamiliar faces were slower when compared to both personally familiar, F(1,23) , po.001, and famous faces, F(1,23) , po.001, which did not differ from each other, F(1,23) No effect of familiarity was observed in the error rates, F(2,46)o1. SCR Trials without artefacts were analyzed by a computerized algorithm. The criterion for a valid response was an increase in skin conductance of at least 0.01 ms between 1 and 7 s after stimulus onset. In 55.1% of the trials these requirements were met. The other trials were defined as nonvalid and amplitude was scored as zero. SCR magnitude was quantified as mean peak amplitude within the response window of all single trials including valid and nonvalid (zero-amplitude) SCRs. SCR amplitude was calculated in the same way but for valid responses only. SCR frequencies were defined as the proportion of stimuli eliciting valid SCR responses. The means and standard deviations of these parameters are shown in Table 2. There were significant effects on SCR magnitude, F(2,46) 5 6.5, po.01, e 5.91, SCR frequency, F(2,46) 5 4.1, po.05, e 5.83, as well as a strong trend for SCR amplitude, F(2,46) 5 3.5, p 5.057, e In response to personally familiar faces, mean SCR magnitudes and frequencies were higher when compared with famous faces, F(1,23) 5 9.6, po.01 and F(1,23) 5 5.3, p 5.06 (uncorrected po.05), respectively, and also when compared with unfamiliar faces, F(1,23) 5 7.4, po.05 and F(1,23) 5 7.7, po.05, respectively. Although only as a trend, the effect on SCR amplitude tended to be the same as for the other parameters (cf. Table 2). In contrast, unfamiliar and famous faces did not significantly differ in any of these measures, Fs(1,23)o1.1. Partly conformable to the predictions of dual-route models, this experiment shows that autonomic responses to personally familiar target faces were both more frequent and larger than those to famous and unfamiliar target faces. Therefore, the familiarity-induced modulation of SCR magnitude and amplitude suggests a stronger involvement of affective components of face processing for personally familiar faces. Unexpectedly and in contrast to previous findings (Tranel et al., 1985) as well as to predictions of dual-route models, no significant differences in SCRs were seen between famous and unfamiliar faces. One possible explanation for this discrepancy may be that the present inclusion of an additional category with strong significance (i.e., Table 1. Mean Correct Reaction Times (RT, in Milliseconds) and Percentage of Errors (PE) for Personally Familiar, Famous, and Unfamiliar Faces in Part 1 of the Experiment RT PE Familiarity type M SD M SD Personally familiar Famous Unfamiliar personally familiar faces) may have dominated the smaller differences between famous and unfamiliar faces. It is worth noting that the results are not explainable simply by an orienting response due to signal value (O hmann, 1979). Because all faces were targets, they bore the same relevance for the task. Furthermore, SCR differences occurred especially within the same response category (familiar faces), which would be hard to explain in terms of signal value with respect to the task. Interestingly, RTs showed a different pattern from the SCR findings, with similar RTs to personally familiar and famous faces and slower responses to unfamiliar faces. Although this pattern may be explained by the task, which placed both types of familiar faces into the same category, the SCRs nevertheless discriminated between these face classes. EXPERIMENT: PART 2FPRIMING In Part 2 of the experiment we investigated priming effects in reaction times and aimed at exploring face recognition units with repetition effects in event-related brain potentials as a function of facial familiarity. Method Participants Sixteen participants (15 women, 1 man), who had also taken part in the first part of the experiment, contributed data to this study. 1 All were strongly right-handed (M , range ); ages ranged from 19 to 27 (M ) years. Stimuli The same stimuli as in Part 1 of the experiment were used. Procedure Directly following the SCR experiment, EEG electrodes were applied and participants received written task instructions. Figure 2 shows the trial sequence. At the beginning of each trial, a white fixation cross appeared for 500 ms, being replaced by a prime face, presented for 500 ms and followed by a green fixation circle. After 1,300 ms the circle was replaced by a target face, presented for 2,000 ms. The interval between prime onsets was 6,300 ms. Participants were asked to indicate by key presses with their left and right index fingers whether the target face was familiar or unfamiliar. No motor response was required to prime faces. For a given participant, the assignment of stimulus category to the left or right response key was the same as in Part 1 of the experiment. Both speed and accuracy were emphasized. Two different feedback tones of 300 ms duration were presented after incorrect (500 Hz) or missing responses (650 Hz). Responses were scored as correct if the appropriate key was pressed between 200 and 2,000 ms after target onset. Mean reaction times were calculated for correct responses only. Throughout the experiment, short breaks were allowed after every 45 trials. The prime for each of the 60 target faces (15 personally familiar, 15 famous, and 30 unfamiliar) could be either the same face (primed condition) or a different face (unprimed condition). 1 Although not all participants from the SCR study were available for the ERP study, the results in Part 1 of the experiment were essentially unchanged even when only these 16 participants were considered.

6 What s special about personally familiar faces? 693 Table 2. Mean Magnitude (in Microsiemens), Amplitude (in Microsiemens), and Frequency (in Percent) for Skin Conductance Responses to Personally Familiar, Famous, and Unfamiliar Faces in Part 1 of the Experiment Familiarity type Magnitude Amplitude Frequency M SD M SD M SD Personally familiar Famous Unfamiliar In the unprimed condition, personally familiar and famous target faces were preceded by unfamiliar primes, and unfamiliar target faces were preceded by personally familiar or famous primes. This allowed us to test repetition priming for both familiar and unfamiliar targets without an impractically large amount of filler trials and appeared appropriate because previous research (Schweinberger et al., 1995) had indicated that responses to unprimed target faces are independent of whether or not the preceding prime face is familiar. The design involved the variables priming (primed vs. unprimed) and familiarity (personally familiar, famous, and unfamiliar). Each of the 60 target faces appeared three times in the primed condition and three times in the unprimed condition, yielding a total of 360 experimental trials. In the unprimed condition a given pair of faces was used only once in order to avoid episodic priming. All trials were shown in randomized order. Recording The electroencephalogram (EEG) was recorded with sintered Ag/AgCl electrodes mounted in an electrode cap (Easy-Capt)at the scalp positions Fz, Cz, Pz, Iz, FP1, FP2, F3, F4, C3, C4, P3, P4, O1, O2, F7, F8, T7, T8, P7, P8, FT9, FT10, P9, P10, PO9, PO10, F9 0, F10 0, TP9, and TP10 (Pivik et al., 1993). The F9 0 and F10 0 electrodes were positioned 2 cm anterior to F9 and F10 at the outer canthi of the left and right eyes, respectively. TP9 and TP10 refer to inferior temporal locations over the left and right mastoids, respectively. The TP10 electrode served as initial common reference and a forehead electrode (AFz) served as ground. Impedances were typically kept below 5 ko. The horizontal electrooculogram (EOG) was recorded from F9 0 and F10 0. The vertical EOG was monitored from two additional electrodes above and below the right eye. All signals were recorded with a band-pass of 0.05 Hz to 40 Hz ( 6dB attenuation, 12 db/octave), and a sampling rate of 200 Hz. Off-line, epochs of 1,700 ms starting 215 ms before target onset were generated from the continuous record. Trials with nonocular artefacts, saccades, and incorrect behavioral responses were discarded. Trials with ocular blink contributions to the EEG were corrected (Elbert, Lutzenberger, Rockstroh, & Birbaumer, 1985) or excluded from data analysis if not enough sample blinks could be obtained, as was the case in three participants. ERPs were aligned to a 215-ms baseline before target onset, averaged separately for each channel and experimental condition, digitally low-pass filtered at 10 Hz with zero phase shift, and recalculated to average reference, excluding the vertical EOG channel. All dependent variables were analyzed by means of ANOVAs with repeated measures on familiarity and priming, epsilon corrected for heterogeneity of covariance, wherever appropriate. Within-subject repeated measures are reported with (a) uncorrected degrees of freedom, (b) the corrected p value, and (c) the epsilon value of the correction factor. Results Performance Reaction times are shown in Table 3. Whereas RTs to unprimed faces appear to be similar in the three familiarity conditions, priming reduced RTs more for both types of familiar faces than for unfamiliar faces. This pattern was confirmed by an interaction between priming and familiarity, F(2,30) , po.001, Figure 2. Trial sequence for Part 2 of the experiment. Shown is an unprimed trial with a target face that was personally familiar to the participants of this study, preceded by an unfamiliar prime face.

7 694 G. Herzmann et al. Table 3. Mean Correct Reaction Times (RT, in Milliseconds) and Percentages of Errors (PE) for Personally Familiar, Famous, and Unfamiliar Target Faces in Part 2 of the Experiment Primed condition Unprimed condition RT PE RT PE Familiarity type M SD M SD M SD M SD Personally familiar Famous Unfamiliar e 5.86, in addition to main effects of priming, F(1,15) , po.001, and familiarity, F(2,30) , po.001, e The interaction is caused by the differential priming effects; there was no familiarity effect in unprimed faces, F(2,30)o1.7, but a strong effect of familiarity for primed faces, F(2,30) , po.001, e Priming effects between personally familiar and famous faces were indistinguishable, F(1,15)o1.7, p4.10, but priming was smaller in unfamiliar faces relative to both personally familiar faces, F(1,15) , po.001, and famous faces, F(1,15) , po.001, respectively. Although relatively small, priming was still significant when tested for unfamiliar faces alone, F(1,15) , po.01. Mean percentage of errors (Table 3) were generally low, except that personally familiar faces were relatively often judged as unfamiliar. This was reflected in a main effect of familiarity, F(2,30) 5 9.7, po.01, e 5.72, with higher error rates for personally familiar faces than for both famous, F(1,15) , po.01, and unfamiliar faces, F(1,15) 5 9.4, po.05, which did not differ from each other. 2 However, effects of priming, Fo1, and the interaction between priming and familiarity, F(2,30) 5 2.3, p4.10, e , were not significant. Thus, error rates do not suggest a speed accuracy trade-off with respect to the priming effects seen in RTs. Event-Related Potentials Figure 3 shows ERPs to personally familiar target faces as typical examples of the observed waveforms. Figure 4 compares ERPs to primed and unprimed faces for all three familiarities at the most important electrode sites. ERPs were quantified with mean amplitude measures, relative to a 215-ms prestimulus baseline, in the time segments , , , , , and ms, relative to target onset. The first and second segments correspond to the occipital P1 and the occipitotemporal N170 peaks in the ERP waveforms, respectively. The P1 is sensitive to variations in relatively early domain-general visual processes, for example, those caused by differences in contrast, brightness, or size (cf. Pfütze et al., 2002). The N170 is a face-specific component supposed to reflect structural encoding (Bentin, Allison, Puce, Perez, & McCarthy, 1996; Eimer, 1998). The subsequent segments were chosen in order to evaluate the N250r ( ms) and the N400 ( ms). For each time segment, ANOVAs were performed analogous to those for the performance data, except for the inclusion of an additional repeated measurement factor electrode (30 levels). Note that, because the average reference sets the mean activity across all 2 It is interesting that the observation of higher percentages of errors is in contrast with the finding of larger SCRs to personally familiar than famous faces. This would seem to exclude an explanation of the SCR effect in terms of overall better knowledge of personally familiar faces. electrodes to zero, condition effects in these ANOVAs are only meaningful in interaction with electrode. Therefore, we report only such interactions butffor brevity s sakefwithout mentioning the electrode factor. If significant effects of priming, familiarity, or of their interaction showed up in the ANOVAs, additional analyses were performed on specific regions of interest (ROIs) in order further to locate these effects. These ROIs were chosen at regions for which the components in question are most clearly visible, and were, for N250r (a) frontal (Fz, F3, F4), (b) temporal (T7, T8, P7, P8, TP9, TP10, P9, P10), and for N400 (c) central-parietal (Cz, Pz, C3, C4, P3, P4). P1. The P1 component can be seen at the occipital electrodes around 125 ms after target onset. No significant effects of the experimental variables on the P1 amplitude were observed, Fso1.8, p4.10. N170. The N170 is most pronounced at occipito-temporal electrodes. The ANOVA of the N170 amplitude yielded effects of priming, F(29,435) 5 2.6, po.05, e 5.18, and familiarity, F(58,870) 5 3.1, po.01, e 5.13, but no interaction between these factors, F(58,870) 5 1.4, p4.10, e The effects of priming and familiarity on N170 amplitude were rather weak and inconsistent and will not be elaborated upon further. 3 N250r (early repetition effect). The N250r is to be seen best at inferior temporal electrodes (e.g., TP10). Moreover, a polarity inversion of this effect is prominent at frontal electrodes (e.g., Fz). Figure 5 depicts the repetition effects by showing the difference waveforms between ERPs to primed and unprimed faces for the three conditions; the topographies of the repetition effects for the different time segments are shown in Figure 6. Inspection of these figures not only shows that (a) the repetition effects reflect an electrical negativity for primed faces over temporal electrodes and a positivity over fronto-central electrodes, and but also suggests that (b) the early repetition effect increased in amplitude from unfamiliar over famous to personally familiar faces. From around 230 ms onward priming caused increased negativity at inferior temporal electrodes. The amplitude measures in both the and ms segments yielded strong effects of priming, Fs(29,435) and 26.4, respectively, pso.001, es There were also effects 3 Several studies (Bentin & Deouell, 2000; Eimer, 2000) have indicated that the N170 is insensitive to the familiarity of faces. Similarly, although there are several studies that report face repetition effects for the N170 or even earlier components (e.g., Braeutigam, Bailey, & Swithenby, 2001), one difficulty with these effects is that they appear to be rather inconsistent across studies. Although we would not completely reject the possibility that there may be small repetition effects on the N170, the present effects in this time range might also reflect temporal overlap with the rising slope of the N250r, rather than differences in the N170 itself.

8 What s special about personally familiar faces? 695 Figure 3. ERPs recorded for primed (solid lines) and unprimed (dashed lines) personally familiar target faces. Recordings are shown for all 30 channels. Arrows indicate the P1, N170, the early repetition effect (N250r), and the late repetition effect (N400). of familiarity, Fs(58,870) and 7.3, pso.001, es 5.20 and.17, and significant interactions between priming and familiarity, Fs(58,870) and 6.6, pso.001, es Pairwise comparisons revealed significant priming effects at each level of familiarity, all Fs(29,435)44.5, all ps o.01, all eso.19. Moreover, priming effects in both time segments differed between personally familiar and famous faces, Fs(29,435) and 4.3, po.001 and po.01, es 5.28 and.18, respectively, and also between personally familiar and unfamiliar faces, Fs(29,435) and 12.4, pso.001, es 5.18 and.20, respectively. In contrast, priming effects differed between famous and unfamiliar faces in the ms segment, F(29,435) 5 3.2, po.05, e 5.14, but not in the preceding ms segment, Fo1. It may be noted that in both segments there were also significant familiarity-induced modulations of amplitude for unprimed faces, Fs(29,435) and 4.0, pso.001, es 5.19 and.20. Bonferoni-corrected pairwise comparison within the unprimed condition revealed significant differences in amplitude between all familiarity conditions at the ms segment, Fs(29,435)44.4, pso.01, eso.23. In the ms time segment amplitudes differed significantly only between personally familiar and unfamiliar, F(29,435) 5 4.8, po.001, eo.24, as well as between famous and unfamiliar faces, F(29,435) 5 5.8, po.001, eo.25, whereas personally familiar faces did not differ from famous faces, Fo In the time segment between 230 and 270 ms the ROI analysis at frontal electrodes revealed significant main effects of priming, F(1,15) , po.001, familiarity, F(2,30) 5 6.7, po.01, 4 The observed familiarity effects within the unprimed condition were significant but weaker than the N250r effect and showed a different topography. They appear to originate from a different source, and will therefore not be analyzed any further. e , and a trend for an interaction of priming and familiarity, F(2,30) 5 2.6, p 5.10, e This interaction was due to priming effect differences between personally familiar and famous faces, F(1,15) 5 7.5, po.05, but not for the other familiarity comparisons, Fs(1,15)o1.7. In the same time segment, temporal electrodes only revealed significant main effects of priming, F(1,15) , po.001, and familiarity, F(2,30) , po.001, e 5.91, but no differences in priming effects across familiarity conditions, F(2,30) 5 1.6, p 5.22, e In the ms segment the ROI analysis revealed similar effects. At both frontal and temporal electrode sites the main effects of priming and familiarity reached significance, pso.001. Moreover, there was a significant interaction of familiarity and priming at frontal electrodes, F(2,30) 5 3.9, p 5.05, e 5.93, this interaction again arising from priming effect differences between personally familiar and famous faces, F(1,15) 5 7.1, po.05. Again, no significant interaction showed up at temporal electrode sites, F(2,30) 5 1.8, p 5.19, e To address the question of whether or not these data provide evidence for separate face recognition units for the affective and cognitive routes, the topographies of the N250r for each category of facial familiarity were analyzed. If scalp topographies of the N250r differ, one may conclude that at least some of the generator sources of this effect are different, lending support for the idea of separate N250r. Interactions in ERP amplitudes of experimental variables with electrode site may derive from differences in the underlying neuronal source configuration only when differences in source strength are ruled out. Therefore, ANOVAs were calculated with factors familiarity and electrode site for the N250r after scaling them to the same overall amplitude within each condition with the average distance of the mean, derived from the grand mean ERPs, as the divisor (McCarthy & Wood,

9 696 G. Herzmann et al. Figure 4. ERPs for personally familiar (first column), famous (second column), and unfamiliar target faces (third column) comparing primed (solid lines) and unprimed conditions (dashed lines) at the most important electrode sites (Pz, Fz, TP10, and P10). Vertical timelines indicate the areas of the early repetition effect, which were used in the ANOVA ( ms and ms). 1985). Recently, Urbach and Kutas (2002) criticized this procedure as being potentially unreliable in its intended application of identifying generator differences, particularly when overall baseline differences exist between conditions, or when multiple sources are present simultaneously. In our experience, overall baseline differences are not likely to be a strong concern in the present study, which used average reference such that any overall differences should be eliminated. In addition, dipole source localization of the N250r to famous faces has suggested a single source in the fusiform gyrus (Schweinberger, Pickering, Jentzsch, et al., 2002). Nevertheless, when using scaling to investigate differences in underlying neuronal source configuration, potential limitations of this procedure should be kept in mind. N250r topographies of priming effects differed significantly across familiarity conditions in the ms segment, F(58,870) 5 4.8, po.001, e Figure 6 suggests that the positive aspect of the N250r peaked in midfrontal regions for unfamiliar faces, but for personally familiar and famous faces it was more pronounced in more posterior central regions. Pairwise comparisons confirmed differences in topography between unfamiliar and both personally familiar faces, F(29,435) 5 9.0, po.001, e 5.18, and famous faces, F(29,435) 5 3.4, po.05, e However, N250r topographies for personally familiar and famous faces were indistinguishable, F(29,435) 5 2.5, p4.10, e N400 (late repetition effect). In both the ms and the ms segment there were significant effects of priming, Fs(29,435) and 5.0, po.001 and po.01, es 5.17 and.15, of familiarity, Fs(58,870) and 2.6, pso.001, es 5.19 and.17, and of their interactions, Fs(58,870) and 2.0, po.001 and po.05, es 5.18, respectively. These priming effects resemble an N400-like modulation of the late positive complex, with more negativity (or less positivity) for unprimed than primed faces at central-parietal locations, and less negativity at prefrontal and lateral frontal locations (see Figures 3 5). Furthermore, Figure 5 suggests that between 330 and 400 ms the N400 priming effect (i.e., the difference between primed and unprimed faces) increased in amplitude from unfamiliar over famous to personally familiar faces. In the ms segment, priming was significant at each level of familiarity, Fs(29,435)44.6, pso.001, es Post hoc comparisons showed differences in the N400

10 What s special about personally familiar faces? 697 F(29,435) 5 3.5, po.05, e 5.17, but was reduced to insignificance for unfamiliar faces, F(29,435) 5 2.7, p4.10, e ROIs analysis of the ms time segment revealed significant main effects of priming, F(1,15) , p 5.001, and familiarity, F(2,30) 5 8.8, p 5.001, e , as well as an interaction between priming and familiarity at central-parietal electrodes, F(2,30) , p 5.001, e Pairwise comparison showed differences in priming effects between personally familiar and famous, F(1,15) 5 9.5, p 5.01, personally familiar and unfamiliar, F(1,15) , p 5.001, and between famous and unfamiliar faces, F(1,15) , p However, in the ms ROI analysis at central-parietal electrodes revealed only significant main effects of priming, F(1,15) 5 9.6, p 5.01, and familiarity, F(2,30) 5 5.7, p 5.01, e 5.96, but no significant interaction of both, Fo1.8. Finally, N400 topographies of priming effects (applying the scaling procedure described above) did not differ significantly across familiarity, Fs(58,870)o2.9, ps4.05. Discussion Figure 5. ERP difference waves (primed minus unprimed) for personally familiar (solid lines), famous (dashed lines), and unfamiliar target faces (dotted lines) at the most important electrode sites (Pz, Fz, TP10, and P10). Vertical timelines indicate the areas of the early repetition effect, which were used in the ANOVA ( ms and ms). priming effect between personally familiar and famous, F(29,435) 5 3.7, p 5.01, e 5.27, personally familiar and unfamiliar, F(29,435) , p 5.001, e 5.21, and between famous and unfamiliar faces, F(29,435) 5 6.2, p 5.001, e In the ms segment, priming was significant for personally familiar, F(29,435) 5 4.9, po.001, e 5.20, and famous faces, At the level of RTwe found least priming for unfamiliar faces and larger but equivalent priming for personally familiar and famous faces. There appears to be no advantage in the cognitive aspects of face processing for personally familiar compared with famous faces. The ERP data revealed an early repetition effect (N250r) around ms that was negative at posterior temporal electrodes but positive at mid-frontal sites, replicating previous reports (Pfütze et al., 2002; Schweinberger et al., 1995; Schweinberger, Pickering, Jentzsch, et al., 2002). Most importantly, N250r amplitude was significantly modulated by facial familiarity. It was smallest for unfamiliar faces, increased to famous faces (see Pfu tze et al., 2002 for similar results), and was largest for personally familiar faces. The sensitivity of the N250r to familiarity indicates that it is not simply a correlate of the repetition of the stimulus but reflects the contact with memory representations for faces. Furthermore affective dimensions, such as likeability or attractiveness, could be thought to have modulated the observed N250r amplitude effects, especially for personally familiar faces. However, the present interstimulus interval between prime and target of 1,300 ms was much too long for possible affective priming, which would require an interstimulus interval below 300 ms (Greenwald, Klinger, & Schuh, 1995). Decisions about the familiarity of a face are supposed to be made at the person identity node level (Burton et al., 1999). Repetition priming has been proposed to involve processing facilitation already during the access to face recognition units or even structural encoding (Pfütze et al., 2002; Schweinberger et al., 1995; Schweinberger, Pickering, Jentzsch, et al., 2002). In this respect, the observed amplitude differences of the N250r for personally familiar compared with famous or unfamiliar faces could be a result of more widespread and stronger neural networks coding these faces. These network differences might result, for example, from a more extensive range of visual experience with personally familiar faces, compared with famous faces. Stronger networks can be assumed to expedite information processing by reducing the threshold for face recognition (Mohr et al., 2002). In contrast to the quantitative differences in N250r amplitudes, the topographies of N250r for personally familiar and famous faces were indistinguishable. This is consistent with