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NeuroImage 11, 98–110 (2000)doi:10.1006/nimg.1999.0521, available online at http://www.idealibrary.com on

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Electrophysiological Correlates of Recollecting Faces of Known andUnknown Individuals

Ken A. Paller, Brian Gonsalves, Marcia Grabowecky, Vladimir S. Bozic, and Shishin YamadaDepartment of Psychology, Northwestern University, Evanston, Illinois 60208-2710

Received March 23, 1999

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We recorded brain potentials from healthy humanubjects during a recognition test in order to monitoreural processing associated with face recollection.ubjects first attempted to memorize 40 faces; halfere accompanied by a voice simulating that person

peaking (e.g., ‘‘I’m Jimmy and I was a roadie for therateful Dead’’) and half were presented in silence. In

he test phase, subjects attempted to discriminate bothypes of old faces (i.e., ‘‘named’’ and ‘‘unnamed’’ faces)rom new faces. Recognition averaged 87% correct foramed faces, 74% correct for unnamed faces, and 91%orrect for new faces. Potentials to old faces were moreositive than those to new faces from 300 to 600 msfter face onset. For named faces, the old–new ERPifference was observed at anterior and posteriorcalp locations. For unnamed faces, the old–new ERPifference was observed only at posterior scalp loca-ions. Results from a prior experiment suggest thathese effects do not reflect perceptual priming of faces.he posterior portion of the old–new ERP differenceas thus interpreted as a neural correlate of retrievalf visual face information and the anterior portion asn indication of retrieval of person-specific semanticnformation. r 2000 Academic Press

INTRODUCTION

A face can function as an effective memory cue,rovoking the retrieval of a wealth of stored informa-ion about an individual. Yet, the brain events thatllow us to remember the people we know are largelynknown. Neuropsychological studies of patients withrain damage suggest that perceiving and remember-ng faces depend on processing in specific corticalegions. Additional information about the relevanthysiological mechanisms may be revealed by measur-ng brain activity during normal face processing. Heree show that measures of the electrical activity of therain can be used toward this end.Person recognition—defined as remembering a known

ndividual and retrieving an assemblage of person- n

98053-8119/00 $35.00opyright r 2000 by Academic Pressll rights of reproduction in any form reserved.

pecific information pertaining to that individual—enerally begins with the perceptual processing of aacial image. Voice information, contextual cues, expec-ations, inferences, and other factors often combine tollow a person to be recognized, but the facial image insolation can be sufficient for person recognition. Theumber of distinct faces that an individual can accu-ately recognize is exceedingly large. People becomexperts at recognizing faces through extensive practicever years and perhaps by virtue of specially evolvedrain mechanisms (Carey, 1992). Clues about the rel-vant neural mechanisms have been provided by behav-oral studies in patients and in healthy individuals,ingle-unit neurophysiology in monkeys, and neuroim-ging and electrophysiological studies in humans (forecent reviews, see De Renzi, 1997; Farah et al., 1998;oung, 1998). Evidence from these various sources cane interpreted within the context of the theoreticalramework for face recognition first put forth by Brucend Young (1986). Separate modules were postulatedor processing physical features of a face, for determin-ng that a face is familiar, for retrieving stored informa-ion about a person, for retrieving a name associatedith a face, for expression analysis, and for facial

peech analysis.Cortical processing mechanisms specialized for face

ecognition have been investigated with a variety ofethods. In monkeys, particular neurons in temporal

ortex respond selectively to faces (Desimone, 1991;errett et al., 1992). In humans, recordings from intra-ranial electrodes have demonstrated face-specific re-ponses from small regions of the left and right fusi-orm and inferior temporal gyri, and electricaltimulation from these same electrodes frequently dis-upted naming of faces (Allison et al., 1994a). Record-ngs from scalp electrodes have also revealed potentialshought to be relatively face-specific (Bentin et al.,996; Botzel and Grusser, 1989; Jeffreys, 1989; Jeffreyst al., 1992). These event-related potentials or ERPsenerally appear 150 to 200 ms after the onset of a facend have been labeled N170 potentials, denoting their

egative polarity and 170-ms peak latency. N170 and

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99MONITORING FACE RECOLLECTION

ther similar potentials have been related not only toace-specific processing, but also to eye-gaze-specificrocessing, and they are thought to reflect corticalctivity in occipitotemporal and posterior fusiform re-ions (Allison et al., 1994b; Puce et al., 1996, 1997).unctional activation of these same cortical regions haslso been associated with face processing using magne-oencephalography or MEG (Linkenkaer-Hansen et al.,998; Sams et al., 1997), positron emission tomographyr PET (Haxby et al., 1996; Sergent et al., 1992), andunctional magnetic resonance imaging or FMRI (Clarkt al., 1996; Haxby et al., 1999; Kanwisher et al., 1997;uce et al., 1995).Although the ability to perceptually analyze faces is

enerally thought to be separate from the ability toemember faces (e.g., Carlesimo and Caltagirone, 1995),t is reasonable to speculate that the inferior occipito-emporal regions where face-specific responses areroduced may also be critical for remembering faces.ccordingly, person recognition may depend on interac-

ions between these cortical regions and regions thattore information pertaining to person identity. Inther words, the complex recollective experience thatan be cued by a face may depend on a network of storedssociations between a visual representation of thatace and other information such as person-specificiographical details, sets of relevant episodic memo-ies, emotional associations, and so on.In the present experiment, we investigated scalp-

ecorded brain potentials that occur when subjectsngage in person recognition in response to viewingacial images. Prior investigations of ERPs and memoryave usually used words instead of faces (for reviews,ee Johnson, 1995; Paller, 1993, in press; Rugg, 1995). Aervasive finding in this literature is that late positiveRP amplitudes tend to be greater for repeated itemsompared to new items, sometimes referred to as anld–new ERP difference or ERP repetition effect. Like-ise, in experiments with faces, a repeat presentationf a face generally yields a different ERP responseompared to the initial response to that face (Barrett etl., 1988; Begleiter et al., 1995; Bentin and McCarthy,994; Bentin and Moscovitch, 1988; Hertz et al., 1994;unte et al., 1997, 1998; Potter and Parker, 1997;

chweinberger et al., 1995; Smith and Halgren, 1987;ommer et al., 1997; Uhl et al., 1990). For example,unte and colleagues (1997) studied ERPs elicited by

aces in implicit and explicit memory tests. In themplicit test, subjects were required to detect famousaces interspersed in a series of nonfamous faces, somef which repeated. In the explicit test, subjects wereequired to discriminate previously seen faces fromther, new faces. In both tests, ERP differences associ-ted with face repetition took the form of increasedositivity from about 300 to 700 ms. ERP differences

ere generally smaller in the implicit test than in the p

xplicit test, with additional topographic differences inhe 300 to 500 ms interval. Presumably, subjects givenhe implicit memory test engaged in less recollectiverocessing in response to repeated faces than did thoseiven the explicit memory test.Paller and colleagues (1999) recorded ERPs to previ-

usly seen faces and new faces, and in addition, twoypes of previously seen faces were compared—someaces were associated with brief biographical informa-ion in a study phase and some were not. Subjects werenstructed to remember the faces with biographies ando forget the others. Despite the artificial nature ofhese circumstances, a face associated with a biographyn this manner can be thought of as corresponding tohe face of a known individual. When those known facesere presented in the experiment, recollective process-

ng of the sort typically associated with person recogni-ion was presumably engaged. ERPs elicited by thoseaces included an enhanced response over posteriorcalp regions and, to a lesser extent, over anterioregions.The present study was designed to determine whether

imilar ERP correlates of face recollection can also bebserved during a yes–no recognition test and withoutifferential instructions to remember. The experimentas thus arranged so that a direct comparison could beade between faces associated with biographical infor-ation and faces presented under circumstances thatere identical except for the absence of associatediographical information. As a shorthand, we will refero the former category of faces as named faces and tohe latter category of faces as unnamed faces. Thisontrast corresponds to the real-world contrast be-ween faces of known and unknown individuals. Facesf both types can potentially provoke recollection, asomeone can remember having seen a face beforeegardless of whether any person-specific biographicalnformation is known. We hypothesized that ERP rep-tition effects would be found for named faces and, to aesser extent, for unnamed faces, which may in bothases reflect recollective processing.

METHODS

Subjects

A group of four men and eight women participated inhe experiment. The mean age was 20.6 years (range 18o 26 years). All subjects were right-handed by self-eport. Subjects gave informed consent and were paidor their participation.

Stimuli

Visual stimuli included photographs of 180 facesrom a 1970s high school yearbook. Each face was

resented in grayscale within a rectangular area

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100 PALLER ET AL.

easuring 12.5 by 16 cm in the center of a computercreen. Faces were viewed from a distance of 135 cmsuch that the rectangular stimuli subtended 5.9 by.5° visual angle). A set of 40 faces was used in thetudy phase. These faces were shown again in the testhase along with 80 new faces. Another 60 new facesere used in a paper-and-pencil recognition test. Each

et of faces included an equal number of women anden. Auditory stimuli were paired with 20 of the faces

n the study phase. These stimuli were spoken by 10omen and 10 men so as to simulate the experience ofeeting the people depicted. Each voice included aame and some brief biographical information (seealler et al., 1999, for additional details).

Procedure

The procedure included a study phase followed imme-

FIG. 1. Schematic representation of experimental trials. (A) Theoices (unnamed faces). (B) The test phase included faces from the stu

iately by a test phase and then a paper-and-pencil w

ecognition test. Each subject was tested individually.o reduce artifactual contamination of EEG recordings,ubjects were instructed to minimize muscle tension,ye movements, and blinks during experimental runs.During the study phase (Fig. 1A), subjects were

nstructed to try to remember a series of people. Theyere told that 20 faces (named faces) would be pre-

ented with a spoken introduction to approximate thexperience of actually meeting these people and that 20aces (unnamed faces) would be presented in silence.ubjects were advised to try to remember all of theeople for a memory test that would be given later.hey were told that the test would assess their ability

o recognize the faces and to recall the names andiographical information of the people who spoke.aces were shown for 300 ms at a rate of 1 every 5 s.he onset of the voice for each named face coincided

dy phase included faces with voices (named faces) and faces withoutphase and new faces, with no auditory components.

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ith the onset of the face presentation. The entire set of

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101MONITORING FACE RECOLLECTION

0 faces was presented three times using differentandom orders. The sets of faces assigned to named andnnamed conditions were counterbalanced across sub-

ects. In other words, each face stimulus from the seterved as a named face for six subjects and as annnamed face for the other six subjects.During the test phase (Fig. 1B), subjects were in-

tructed to respond after each face according to whetherhe face shown was old or new, pressing a button in oneand or the other (right hand for old for half of theubjects, left hand for old for the others). They werelso told to use this as an opportunity to think about theiographical information that was to be rememberedor the subsequent memory test. Faces were shown for00 ms at a rate of 1 every 3 s. Faces were presented inour runs without any auditory stimuli. Named andnnamed faces were repeated across runs, whereasew faces each appeared on only one occasion. Becausee wished to make comparisons with results from arior experiment, we used stimulus sequences identicalo those used previously, even though the task washanged. In the prior experiment (Paller et al., 1999),arget events were included by selecting 2 new faces, 2amed faces, and 2 unnamed faces in each run to beresented twice in a row. In the present experiment,ubjects were told that when a face appeared twice in aow, they should respond the same way for both presen-ations. Responses to these immediately repeated facesere excluded from all analyses. Thus, the remaining

aces in each of the four runs included a randomlyrdered set of 60 faces: the 20 named faces, the 20nnamed faces, and the 20 new faces.For the paper-and-pencil recognition test given at the

onclusion of the experiment, subjects used a set of fiveages showing 20 faces per page. These 100 facesncluded the 40 faces from the study phase randomly

ixed with 60 new faces not otherwise used in thexperiment. Subjects were asked to place a letter in aorresponding box for each of the 20 named faces andach of the 20 unnamed faces and to write down theame and biographical information for each namedace. Approximate wording was sufficient for recallediographical information to be scored as correct.

Electrophysiology

Electroencephalographic recordings were made from1 scalp electrodes embedded in an elastic cap attandard locations (Fpz, Fz, Cz, Pz, Oz, Fp1, Fp2, F3,4, F7, F8, C3, C4, P3, P4, O1, O2, T3, T4, T5, T6). A leftastoid reference electrode was used online and the

eference was changed offline to the average of left andight mastoid recordings. Two channels were used foronitoring horizontal and vertical eye movements and

rials contaminated by electroocular artifacts werexcluded from the analyses (7.2% on average in the test

hase). Biosignals were amplified with a 0.1 to 100 Hz

and pass and sampled at a rate of 250 Hz. ERPs wereomputed for 1024-ms epochs beginning 100 ms prior totimulus onset. The 300- to 600-ms interval was se-ected for initial analyses as this interval was used inur earlier study (Paller et al., 1999). Subsequentnalyses to investigate ERP time course were con-ucted over 100-ms latency intervals. ERP measure-ents were evaluated using analysis of variance

ANOVA), and critical F ratios were based on degrees ofreedom adjusted according to the Huynh–Feldt proce-ure when needed to control for Type I errors inepeated-measures designs.

RESULTS

Behavioral results are summarized in Table 1. Asxpected, recognition was better for named faces thanor unnamed faces. This difference was significant foroth the test-phase recognition test [t(11) 5 3.6, P 5.004] and the subsequent paper-and-pencil recogni-ion test [t(11) 5 2.5, P 5 0.03]. For named faces,uccessful name recall averaged 33.8% (SE 5 7.3) anduccessful recall of the other biographical informationveraged 60.0% (SE 5 5.6).Reaction time results for correct trials in the test

hase (Table 1) showed that responses were equiva-ently fast for named faces and unnamed faces [t(11) ,]. Responses to both types of old faces were faster thanesponses to new faces [t(11) 5 3.5, P 5 0.01 and t(11) 5.3, P 5 0.04, respectively].Electrophysiological recordings during the test phase

evealed systematic differences as a function of condi-ion, as shown in Fig. 2. First, note that ERPs computedcross all trials were quite similar to ERPs computedor correct trials. However, there was insufficient statis-ical power to analyze ERPs separately for incorrectrials. Given our concern with identifying neural corre-ates of accurate retrieval, ERP results for correct trialsill be emphasized. Analyses of the two study ef-

ects—(1) ERPs to named versus new faces and (2)RPs to unnamed versus new faces—will be described

TABLE 1

Behavioral Results from Memory Tests (SE Shownin Parentheses)

Measure

Condition

Named faces Unnamed faces New faces

est-phase recognitionaccuracy (% correct) 87.2 (3.0) 73.9 (5.2) 90.9 (2.6)

aper-and-pencil rec-ognition accuracy (%correct) 73.3 (4.7) 64.2 (4.6) 89.3 (1.8)ean reaction time(ms) 770 (30) 784 (36) 848 (26)

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102 PALLER ET AL.

n turn. Both of these study effects (or old–new ERPifferences) can also be viewed as difference wavesFig. 3).

Mean ERP amplitudes from the five midline scalpocations were initially measured over the intervalrom 300 to 600 ms and these measurements wereubmitted to ANOVAs with Condition (named vs new ornnamed vs new) and Location as factors (see Table 2).he first ANOVA showed that ERPs were significantlyore positive for named than for new faces. Theondition by Location interaction reflected the finding

hat this study effect was significant at all midlineocations except the most anterior one. ERP compari-ons between unnamed and new faces revealed aimilar pattern. Midline ERPs from 300 to 600 ms werelso significantly more positive for unnamed than forew faces. The Condition by Location interaction re-ected the finding that this study effect was significantnly at the two most posterior locations. In other words,tudy effects at posterior locations (Pz and Oz) wereeliable for named and unnamed faces, whereas studyffects at anterior locations (Fz and Cz) were reliablenly for named faces. The topography of the two study

FIG. 2. ERPs recorded during the test phase for named faces, unocations arranged from anterior (top) to posterior (bottom), including

ffects can be viewed as a series of interpolated maps 5

reated from ERP difference measurements over con-ecutive 100-ms intervals (Figs. 4 and 5).Subsequent analyses were conducted to determine

he time course of the study effects by analyzing ERPsver 100-ms intervals. First, analyses focused on re-ults from the midline parietal location, where studyffect amplitudes were largest. ERPs to named facesere significantly more positive than ERPs to new

aces for all three intervals from 300 to 600 ms [F(1,11) 5.42, 10.61, and 11.85, P 5 0.01, 0.008, and 0.006,espectively]. Differences were nonsignificant for allther intervals, although there was a marginal differ-nce from 200 to 300 ms [F(1,11) 5 3.8, P 5 0.08]. ERPso unnamed faces were also significantly more positivehan ERPs to new faces for all three intervals from 300o 600 ms [F(1,11) 5 10.84, 19.02, and 12.17, P 5 0.007,.001, and 0.005, respectively] and nonsignificant forll other intervals. Additional analyses were conductedt the midline frontal location, where only the named–ew ERP difference was significant. This differenceppeared to begin later than the posterior difference, ast was nonsignificant from 300 to 400 ms [F(1,11) 5.68, P 5 0.13], significant from 400 to 500 ms and from

ed faces, and new faces. Recordings shown were from midline scalptrials (left) or only correct trials (right).

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00 to 600 ms [F(1,11) 5 14.00 and 6.61, P 5 0.003 and

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103MONITORING FACE RECOLLECTION

.03, respectively], and nonsignificant for all otherntervals. In short, the posterior difference was presentrom 300 to 600 ms, whereas the anterior differenceas present from 400 to 600 ms.To directly assess the reliability of anterior ERP

ifferences between named and unnamed faces, ERPsere analyzed over consecutive 100-ms intervals atidline electrodes. For the 400- to 500-ms interval, the

ifference was significant at Fpz [F(1,11) 5 6.49, P 5.03], marginal at Fz [F(1,11) 5 4.09, P 5 0.07], andonsignificant at Cz, Pz, and Oz [F(1,11) , 1]. For other

ntervals differences were nonsignificant. In addition,RP differences from 400 to 500 ms from all lateral

ocations were submitted to a Condition by Hemispherey Location ANOVA. Although there was a tendency forRP differences between named and unnamed faces toe larger over the right hemisphere (Fig. 3), all effectsnvolving Hemisphere were nonsignificant.

DISCUSSION

The study-phase manipulation in the present experi-ent provided richer encoding for named faces than for

nnamed faces. The contrast between named and un-amed faces was associated with two differences in

ater memory. First, named faces tended to provoke theetrieval of stored biographical information from the

faces from ERPs to old faces, including only correct trials. Recordings

TABLE 2

ERP Differences between Conditions

Comparison µV SE F P

Named–new facesMidline mean 1.76 0.51

Main effect ofCondition *11.92 0.005

Condition 3 Locationinteraction *4.68 0.02

Midline locationsFpz 0.79 0.44 3.21 0.10Fz 1.50 0.50 *9.10 0.01Cz 1.93 0.67 *8.20 0.02Pz 2.64 0.76 *12.06 0.005Oz 1.95 0.48 *16.82 0.002

Unnamed–new facesMidline mean 1.33 0.45

Main effect ofCondition *8.88 0.01

Condition 3 Locationinteraction *6.97 0.001

Midline LocationsFpz 0.23 0.43 0.28 0.61Fz 0.87 0.57 2.38 0.15Cz 1.31 0.64 4.15 0.07Pz 2.33 0.58 *16.26 0.002Oz 1.92 0.37 *26.38 0.0003

Note. An asterisk adjacent to the F value indicates a statisticallyignificant effect. Degrees of freedom were 4,44 for each Condition 3

FIG. 3. ERP difference waves computed by subtracting ERPs to new

tudy phase, whereas this was not possible for un-

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104 PALLER ET AL.

FIG. 4. Topographic maps of ERP differences across the scalpnterpolation was applied to data obtained from each electrode locatio

for ERPs to named faces minus ERPs to new faces. A surface splinen (indicated by small circles on each schematic view of a head as viewed

rom above). Maps represent mean amplitude differences computed for consecutive 100-ms intervals starting at 0 and ending at 800 ms.

105MONITORING FACE RECOLLECTION

FIG. 5. Topographic maps of ERP differences between unname

d faces and new faces. Topographic maps were created as in Fig. 4.

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106 PALLER ET AL.

amed faces. Second, superior recognition performanceas observed for named compared to unnamed faces.ubjects recognized named faces more accurately, buteaction times for correct responses did not differetween named and unnamed faces. Furthermore,eaction time distributions for named and unnamedaces appeared extremely similar. Thus, ERP compari-ons for named versus unnamed faces in the test phaseere not complicated by confounding differences in

eaction time, nor were there any systematic physicaltimulus differences (by virtue of the counterbalancedxperimental design). Although significant old–newRP differences were present for both types of old faces,

or named faces these effects were found at anterior andosterior scalp locations (Fig. 4), whereas for unnamedaces these effects were restricted to posterior scalpocations (Fig. 5).

In prior experiments conducted with the same namednd unnamed faces, subjects were instructed in thetudy phase to remember the named faces and to forgethe unnamed faces (Paller et al., 1999). In a test phasen which perceptually degraded faces were presentedor fame decisions (i.e., ‘‘famous’’ vs ‘‘nonfamous’’),riming was measured as a facilitation in both decisionccuracy and latency (Paller et al., 1999, Experiment). Importantly, the magnitude of priming did not differetween the two types of studied faces (referred to asemember faces and forget faces). Indeed, differentialrocessing induced by remember versus forget instruc-ions at study generally affects later recall and recogni-ion but does not affect priming performance (Basden etl., 1993; Golding and MacLeod, 1998; Johnson, 1994;aller, 1990; Roediger and McDermott, 1993). The highegree of similarity between procedures used in ourrior ERP experiment (Paller et al., 1999, Experiment) and in the present experiment allows for straightfor-ard cross-experiment comparisons. The only two ways

n which the design of the present experiment differedere that (1) all faces shown in the study phase were toe remembered and (2) the task in the test phase was toake overt recognition responses. Accordingly, it is

easonable to speculate that priming would likewise beatched between named and unnamed faces in the

resent experiment. In contrast, recognition was supe-ior for named compared to unnamed faces whether orot directed forgetting instructions were included.ERPs elicited in the test phase in the prior ERP

xperiment (Paller et al., 1999, Experiment 2) wereound to differ between remember and forget faces.hese effects were interpreted in light of the behavioralesults that the study-phase manipulation influencedecognition but not priming. Note that no overt recogni-ion responses were made when ERPs were recorded.ubjects were instructed to retrieve learned biographi-al information when shown a remember face but to

ake no overt response for either remember faces or i

orget faces. Recollection, but not priming, thus differedetween remember and forget faces. Electrophysiologi-al correlates of priming would thus be absent inomparisons between the two types of old faces (thoughRP correlates of priming have been observed withords, e.g., Paller and Gross, 1998). ERP differencesetween the two types of old faces (remember faces–orget faces) were thus interpreted as electrophysiologi-al correlates of recollective processing, divorced fromhe influence of priming and other nonspecific factors.igure 6 shows the spatiotemporal pattern of theseffects.Inspection of Figs. 4, 5, and 6 suggests that similar

europhysiological phenomena were recorded acrossxperiments, although there were differences in theatency of the observed response. Apparently, theselectrophysiological manifestations of face recollectionere evident whether or not subjects made overt recog-ition responses and whether or not faces were associ-ted with biographical information. Interestingly, theatency of old–new effects was shorter in the presentxperiment than in the prior experiment. A reasonablexplanation for this difference is that retrieval process-ng occurred more quickly following face presentationsn the present experiment due to the recognition taskequirement, which demanded a quick manual re-ponse to each face. The comparison across experi-ents is also relevant for several other reasons. Old–

ew ERP effects in the present experiment could haveeen influenced by response-related processing, givenhat reaction times differed between old and new faces.owever, the old–new ERP differences cannot be ex-lained by a relative increase in temporal variability ofrocessing elicited by new face presentations, becauseeaction time variability was less for new faces com-ared to old faces, as shown in Table 1.The contrast between named–new and unnamed–

ew ERP differences in the present experiment makest possible to ask whether a portion of the effect ispecifically related to retrieval of biographical informa-ion. Again, note that this named/unnamed contrast isree from any physical stimulus effects (due to counter-alancing) and from response factors (given the ab-ence of corresponding reaction time differences). If oneere to assume that nearly all of the old–new ERP

ffect reflected biographical retrieval, then the effectould be expected to be much larger for named faces

han for unnamed faces. On the contrary, if one were tossume that nearly all of the old–new ERP effecteflected face retrieval, then the effect would be ex-ected to be the same for named and unnamed faces.Indeed, at posterior locations the old–new ERP effectas highly similar for named and unnamed faces. Thisosterior portion of the effect can thus be taken as anndex of face recollection associated with visual process-

ng of the facial image just presented and of retrieved

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107MONITORING FACE RECOLLECTION

FIG. 6. Results from Paller et al. (1999) for the ERP difference bes in Figs. 4 and 5.

en remember faces and forget faces. Topographic maps were created

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108 PALLER ET AL.

epresentations of the face viewed at study. At anteriorocations, the old–new ERP effect was observed foramed faces but was smaller and unreliable for un-amed faces. This anterior portion of the effect can thuse taken as an index of person recollection connected tohe biographical information heard at study.

In addition, part of the anterior portion of the old–ew ERP effect for named faces may reflect frontalctivity engaged in the service of strategic retrievalperations. Prior neuroimaging and ERP results sug-est that both left and right frontal regions tend to bectivated during retrieval, although left frontal regionsppear to be particularly relevant for evaluation pro-esses critical for accurate retrieval (e.g., Buckner,996; Fletcher et al., 1997; Nolde et al., 1998; Nyberg etl., 1996; Ranganath and Paller, 1999; Tulving et al.,994; Wilding, 1999; Wilding and Rugg, 1996). Simi-arly, the problem of retrieving the appropriate namend biographical information for each named face mayall on prefrontal processing for accurate retrieval toake place. Prefrontal regions could also contribute torocessing of contextual information that occurs afternitial face retrieval; however, the early timing of thenterior portion of the old–new ERP effect suggestshat it does not reflect postretrieval processing.

An alternative explanation for the ERP differencesor named versus unnamed faces is that they reflectifferential recognition accuracy for the two types oftudied faces. This alternative could apply even fornalyses restricted to correct trials, because recogni-ion could have been stronger for named than fornnamed faces (e.g., fewer lucky guesses). Nonetheless,opographically specific differences for named versusnnamed faces, as observed here, would not be pre-icted based on differences in recognition strengthlone. The fact that ERPs at posterior scalp locationsere so remarkably similar for named and unnamed

aces suggests that this portion of the old–new ERPffect reflected memory-related processing that sup-orted accurate recognition judgments in both condi-ions.

These results provide a foothold for further researchimed at establishing the nature of neural processingesponsible for person recognition. Prosopagnosic im-airments in which patients fail to recollect familiaraces generally result from damage to inferior temporalegions, although the precise anatomical details of thisssociation are controversial and perhaps quite vari-ble across patients (e.g., Damasio et al., 1982; Deenzi, 1997; Ettlin et al., 1992). Prior neuroimagingesults with PET and FMRI have associated variousrain regions with memory for known and unknownaces (Andreasen et al., 1996; Dubois et al., 1999; Gornoempini et al., 1998; Haxby et al., 1996; Kapur et al.,995; Sergent et al., 1992). For example, right prefron-

al, bilateral parietal, and ventral occipital regions

ere implicated by Haxby and colleagues (1996). Moreimited regions of activation in the fusiform gyrus, leftingual gyrus, and right parietal cortex were found byndreasen and colleagues (1996). Additional studiesre needed to delineate the various cortical networksequired for person recognition and link them to spe-ific memory functions. Old–new ERP effects appearedo reflect multiple aspects of memory for faces. Thesencluded (a) processing of visual information correspond-ng to the match between a recognition probe andtored representations of facial images viewed attudy—which was associated with posterior ERP differ-nces beginning at approximately 300 ms—and (b)trategic processing critical for retrieving person-pecific biographical information heard at study—hich was associated with anterior ERP differenceseginning at approximately 400 ms.

ACKNOWLEDGMENTS

This research was supported by Grant NS34639 from the Nationalnstitute of Neurological Diseases and Stroke. We thank Ted Whalenor technical support.

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