Download pdf - Bioelectrical echoes from evaluative categorization: II. A late positive brain potential that varies as a function of attitude registration rather than attitude report

Journal of Personality and Social Psychology1995, Vol. 68, No. 6, 997-1013

Copyright 1995 by the American Psychological Association, Inc.0022-3514/95/S3.0O

Bioelectrical Echoes From Evaluative Categorization:II. A Late Positive Brain Potential That Varies as a

Function of Attitude Registration Rather Than Attitude Report

Stephen L. Crites Jr.University of Texas at El Paso

John T. Cacioppo, Wendi L. Gardner,and Gary G. Berntson

Ohio State University

We report evidence of both correspondence and independence between participants' attitude reportand a late positive potential (LPP) of the event-related potential. Attitude reports and LPPs to posi-tive, neutral, and negative stimuli that were preceded by positive stimuli were recorded while partic-ipants either reported accurately their attitudes or misreported neutral or negative attitudes. Evalu-atively inconsistent, in contrast to consistent, stimuli evoked a larger LPP regardless of whetherparticipants reported accurately or misreported their attitudes. These results were replicated in asecond study in which attitude reports and LPPs to negative, neutral, and positive stimuli that werepreceded by negative stimuli were recorded. Findings suggest that the LPP evoked during evaluativejudgments reflects attitude categorization rather than attitude report processes and can potentiallyassess attitudes that people are unwilling to report.

The scientific study of attitudes was spawned by Thur-stone's (1928) article entitled "Attitudes Can be Mea-sured." Thurstone's insight was to treat the attitudes evokedby stimuli as evaluative percepts that establish "potentialaction" toward stimuli. This application of the theory andmethods from psychophysics to the study of attitudes en-abled attitudes to be measured through the use of estab-lished psychophysical methodologies and laid the ground-work for contemporary self-report attitude measures(McGuire, 1985). As Thurstone was careful to point out,however, there is no guarantee that an expressed attitude isa valid index of an individual's evaluative percept.

There comes to mind the uncertainty of using an opinion as anindex of attitude. The man may be a liar.... Neither his opinionsnor his overt acts constitute in any sense an infallible guide to thesubjective inclinations and preferences that constitute his attitude.

Stephen L. Crites Jr., Department of Psychology, University of Texasat El Paso; John T. Cacioppo, Wendi L. Gardner, and Gary G. Berntson,Department of Psychology, Ohio State University.

This research was conducted as part of a doctoral thesis by StephenL. Crites Jr. under the supervision of John T. Cacioppo. Preparationof this article was supported by a National Institute of Mental HealthTraineeship to Stephen L. Crites Jr., a National Science FoundationFellowship to Wendi L. Gardner, and a National Science Foundationgrant. We would like to thank David Lozano for his technical assistanceand Nicki Harrelson and Jennifer Hammond for their assistance in datacollection. Preliminary reports of this research were presented at theannual meeting of the Society for Psychophysiological Research, Rot-tach-Egern, Germany, October, 1993.

Correspondence concerning this article should be addressed to Ste-phen L. Crites Jr., Department of Psychology, University of Texas, ElPaso, Texas 79968.

Therefore, we must remain content to use opinions, or other formsof action, merely as indices of attitude. (Thurstone, 1928, p. 532)

Thus, although attitudes have been conceptualized, at leastimplicitly, as evaluative percepts that guide behavior, there is noguarantee that a given behavior or an expressed attitude is avalid index of an individual's evaluative percept. Indeed, nu-merous situational and dispositional factors have been identi-fied that can selectively influence behavioral expressions of atti-tudes, including variable perspectives (Ostrom, 1970; Ostrom& Upshaw, 1968), response acquiescence (Cornbach, 1946,1950), evaluation apprehension or self-presentational motives(Leary & Kowalski, 1990; Tedeschi, 1981), demand character-istics (Orne, 1962, 1969), and the tendency to seek social ap-proval (Crowne & Marlowe, 1964; Edwards, 1957). Althoughprocedures have been developed for increasing the accuracy ofattitude reports in situations in which individuals would other-wise be unwilling to report their attitudes (e.g., Dawes & Smith,1985; Jones &Sigall, 1971;Scott, 1968), these procedures ulti-mately depend on the naivete of individuals to the assumptionsunderlying the procedures. If people are aware, for instance,that a device in a bogus pipeline procedure (Jones & Sigall,1971) cannot index their evaluative percept of an object, theymay not feel compelled to report accurately their attitude to-ward that object (Ostrom, 1973).

Researchers since Rankin and Campbell (1955), therefore,have endeavored to develop procedures that use physiologicalresponses to assess attitudes, because physiological responseswere believed to be less sensitive to nonattitudinal factors thatcan distort the behavioral expression of attitudes. Initially, re-search focused on autonomic responses because noninvasiveautonomic measures were readily available, the autonomic ner-vous system was thought to subserve specific emotional states(James, 1884), and early reports had related the magnitude of

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998 CRITES, CACIOPPO, GARDNER, AND BERNTSON

autonomic responses to the intensity of emotional stimuli(McCurdy, 1950). Cumulative research, however, indicatesthat autonomic responses (e.g., electrodermal activity, heartrate, pupillary responses) vary as a function of the intensity ofan individual's emotional reaction to a stimulus as well as non-attitudinal factors in the assessment context (see reviews byCacioppo & Sandman, 1981; Zanna, Detweiler, & Olson, 1984;see, also, Zajonc & Mclntosh, 1992). More recently, facial elec-tromyographic (EMG) responses, particularly over the brow(corrugator supercilii) and cheek (zygomaticus major) regions,have been found to vary as a function of the valence and inten-sity of emotional reactions to a stimulus (Cacioppo, Petty,Losch, & Kim, 1986), and specific forms of facial EMG re-sponse have been found to serve as a marker for positive versusnegative emotional states (Cacioppo, Martzke, Petty, & Tassi-nary, 1988; Teasdale & Rezin, 1978). Using facial EMG re-sponses as an attitude measure, however, may be problematicbecause (a) the extremity of attitudes that lack a strong emo-tional basis (e.g., instrumental, in contrast to consummatory,attitudes) may be underestimated (Cacioppo et al., 1986), and(b) people are capable of masking, amplifying, or distorting thefacial EMG responses displayed in response to an emotionalstimulus (Cacioppo, Bush, & Tassinary, 1992). Thus, auto-nomic and somatic responses, like self-reports, are limited intheir ability to examine attitudes because these efferent re-sponses follow attitude (i.e., evaluative) categorizations and aresusceptible to response distortions. Because of these limitationswith autonomic and somatic responses, we recently applied the-ory and methods from event-related brain potentials to thestudy of attitudes (Cacioppo, Crites, Berntson, & Coles, 1993;Cacioppo, Crites, Gardner, & Berntson, 1994).

The present research builds on earlier work by examiningwhether a late positive potential (LPP) of the event-relatedbrain potential (ERP) is sensitive to variations in attitude cate-gorizations but not attitude reports. Event-related brain poten-tials reflect the temporal sequence of information processingoperations associated with a discrete event (e.g., the presenta-tion of an attitude object) and thus may represent a method ofexamining evaluative categorizations that does not depend onself-report judgments. The positive and negative electrical po-tentials of the ERP, which can be recorded from electrodesplaced on the scalp, are produced by a sequence of temporallyactivated neural units associated with the processing of infor-mation related to a discrete event. Cumulative research suggeststhat one component of the ERP—a late positive potentialknown as the P300, or P3b—varies as a function of categoriza-tion and not response operations (e.g., see Coles, Gratton, &Fabiani, 1990; Donchin, Karis, Bashore, Coles, & Gratton,1986, for reviews). In typical research on the P300, simplestimuli representing two distinct categories (e.g., high and lowtones) are presented to participants in long sequences in whichstimuli from one category have a low probability of occurrenceand stimuli from the other category have a high probability ofoccurrence (i.e., oddball paradigm). When participants catego-rize stimuli in these oddball sequences along some dimension(e.g., high vs. low tones), categorically inconsistent stimuli(e.g., a high tone that is preceded by a sequence of low tones)rather than categorically consistent stimuli (e.g., a high tone

that is preceded by a sequence of high tones) evoke a large LPP(i.e., P300) with a maximal amplitude over the midline centro-parietal areas of the scalp (e.g., Duncan-Johnson & Donchin,1977; Fabiani, Gratton, Karis, & Donchin, 1987; Squires,Wickens, Squires, & Donchin, 1976). Furthermore, two relatedpieces of evidence suggest that the P300 reflects categorizationoperations that largely precede behavioral response selectionand execution. First, factors that affect selectively response se-lection and execution processes do not affect the amplitude (orlatency) of the P300, although they do affect behavioral re-sponses (e.g., Magliero, Bashore, Coles, & Donchin, 1984; Mc-Carthy & Donchin, 1981; Ragot, 1984). Second, research onlie detection that has used the P300 has demonstrated that cat-egorically inconsistent stimuli evoke a large P300 even whenindividuals report that inconsistent stimuli are categoricallyconsistent with the preceding stimuli (Allen, Iacono, & Dan-ielson, 1992; Farwell & Donchin, 1991; Rosenfeld, Angell,Johnson, & Qian, 1991).

Drawing on the P300 literature, we reasoned that the evalua-tive categorizations underlying attitude judgments could be ex-amined using late positive (i.e., P300-like) potentials of theERP if an experimental task were developed in which an indi-vidual's attitude served as the criterion along which stimuli wereimplicitly categorized. In this task, participants were requiredto attend to and evaluatively categorize attitude stimuli thatwere presented in short sequences; each of these short sequenceswas constructed such that a specific stimulus (i.e., targetstimulus) was evaluatively consistent or inconsistent with thepreceding stimuli. To examine whether an LPP varied as a func-tion of the evaluative inconsistency of the eliciting stimulus,ERPs were recorded to liked and disliked (target) stimuli thatwere presented within short sequences of either liked or disliked(nontarget) stimuli. As expected, evaluatively inconsistentstimuli (e.g., a negative stimulus preceded by a series of positivestimuli) elicited a larger amplitude LPP than evaluatively con-sistent stimuli (e.g., a negative stimulus preceded by a series ofnegative stimuli; Cacioppo et al., 1993, 1994). Furthermore,this LPP enhancement to an inconsistent stimulus was obtainedwhether the evaluatively inconsistent stimulus was positive ornegative; in fact, stimulus valence per se did not affect the LPP.

The purpose of the present experiments was to investigatewhether the LPP that is evoked by evaluative categorizationsis affected by instructions that alter the attitude report. SinceThurstone's (1928) inaugural article, researchers have recog-nized that self-reports are limited to attitudes that people arewilling to report because individuals can intentionally misrep-resent or modify the expression of their attitude. Furthermore,the attitudes that may be the most important to measure accu-rately are those that people are often unwilling to disclose (e.g.,socially unacceptable attitudes). If, as hypothesized, the LPPvaries as a function of categorization and not response pro-cesses, the LPP can potentially be used to assess attitudes thatpeople intentionally misrepresent. Thus, these experiments ex-amined whether the enhancement of the LPP amplitude to eval-uatively inconsistent stimuli would be attenuated or eliminatedwhen the presentation of an evaluatively inconsistent stimulusled to a change in the implicit attitude categorization but not inthe overt attitude report.

BIOELECTRICAL ECHOES 999

Study 1

Method

Overview. To ensure that each stimulus was categorized along anevaluative dimension even when participants misreported their attitudetoward a stimulus, three distinct categories of evaluative stimuli (i.e.,positive, neutral, and negative) were minimally required. Trait adjec-tives served as experimental stimuli, and the participants' task was toread each trait and to either report accurately or misreport their attitudetoward an individual described by that trait. Given a consensus aboutwhich traits are positive, neutral, and negative (Anderson, 1968), theuse of traits as stimuli made it possible to know in advance which stimuliwould evoke positive, neutral, or negative attitudes toward individualsdescribed by the traits. During half of the experimental sequences, par-ticipants were instructed to report accurately their attitudes toward allthree categories of evaluative stimuli. During the remaining sequences,half of the participants were instructed to report their neutral attitudesas positive and to report accurately positive and negative attitudes,whereas half of the participants were instructed to report their negativeattitudes as positive and to report accurately positive and neutral atti-tudes. Because participants were always required to report accuratelytheir attitudes toward two of these three categories of evaluative stimuli,participants had to discriminate among positive, neutral, and negativetraits to perform the task even when they were misreporting negative orneutral attitudes as positive. If only two categories of stimuli (e.g., posi-tive and negative) were used, participants would have to process onlythat some stimulus was presented when instructed to misreport theirattitudes because all stimuli would be reported as belonging to a singleevaluative category.

Participants. Twenty-two Introductory Psychology students (13 fe-male and 9 male) at Ohio State University participated in the experi-ment in partial fulfillment of a course requirement.1 All participantswere right-handed and in good health. We randomly assigned 11 partic-ipants to the negative-focus condition, in which they periodically mis-reported the valence of negative attitudes, and we randomly assigned 11participants to the neutral-focus condition, in which they periodicallymisreported the valence of neutral attitudes.

Stimulus materials. We selected three categories of attitudinal stim-uli from Anderson's (1968) list of trait adjectives: (a) the pool of posi-tive traits were the 52 most positively rated adjectives (e.g., honest), (b)the pool of neutral traits were the 10 adjectives whose mean rating wasclosest to 3.00 on Anderson's 7-point (0-6) scale (e.g., hesitant), and(c) the pool of negative traits were the 10 most negatively rated adjec-tives (e.g., dishonest). Because a short sequence of positive trait adjec-tives always preceded the positive, neutral, and negative traits to whichelectroencephalographic (EEG) activity was recorded (i.e., targettraits), a greater number of positive trait adjectives was needed to equatefor the number of times that each trait adjective was presented. Thecombination of 52 positive, 10 neutral, and 10 negative trait adjectivesallowed each trait to be presented an equal number of times during thecourse of the experiment.

Procedure. After arriving at the laboratory, participants were toldthat previous experiments had revealed that an individual's brain activ-ity could be used to determine whether the individual liked or dislikedan item. The experimental instructions then differed slightly for the 11participants who were told to focus on negative traits (i.e., periodicallymisreport negative traits as positive) and the 11 participants who weretold to focus on neutral traits (i.e., periodically misreport neutral traitsas positive). The experimenter explained that the purpose of this exper-iment was to determine whether people's brain activity revealed theirnegative (neutral) attitude toward another individual even if they re-ported that their attitude was positive. Participants were informed thattheir attitudes toward people who possessed different personality traits

were going to be examined by showing them a number of trait adjectivesand asking them to report accurately or misreport their attitudes towardpeople who possessed these traits. In some cases, they would be asked toreport accurately their attitude whenever they felt negatively (neutrally)about the individual described by the trait. In other cases, however, theywould be asked to express a positive attitude whenever they felt nega-tively (neutrally) about the individual described by the trait. This in-struction was designed to mimic instances such as those anticipated byThurstone (1928) in which individuals intentionally misrepresent ormodify the expression of their attitude. Participants then read andsigned an informed-consent form and completed a health survey. Next,the electrodes were attached, and participants were taken to a sound-attenuated, electrically shielded room and seated in a comfortable, re-clining chair. A monitor was located approximately 0.5 m in front ofthe participant, and a hidden video camera was used to monitor partic-ipants during the experiment.

Once participants were in the experimental room, they were in-formed that trait adjectives would be presented in sequences of six andthat each trait described a different individual. Participants were thentold that their task was to indicate, by pressing a key on a keypad,whether they would like, feel neutrally toward, or dislike an individualwho was characterized by the trait presented on the screen. The experi-menter emphasized that speed of response was unimportant and, tofurther foster deliberate attitude responding, instructed the participantsto respond only after the trait was removed from the screen. In addition,participants were asked to make their responses with their right indexfinger (i.e., their preferred index finger) to ensure that the bioelectricalactivity associated with performing the behavioral response was com-parable across conditions.

Once this facet of the task was clear to participants, the experimenterexplained that sometimes they would be asked to express a positive at-titude whenever they felt negatively (neutrally) toward an individual butto accurately express positive and neutral (negative) attitudes. Partici-pants were told that a message would appear before each sequence in-structing them to either (a) respond accurately whenever they felt posi-tively, neutrally, or negatively toward an individual described by a traitpresented during that sequence or (b) respond as if they had a positiveattitude whenever they felt negatively (neutrally), but to respond accu-rately whenever they felt positively or neutrally (negatively), toward anindividual described by a trait presented during that sequence. Afterthese instructions, participants were given 5 min to adapt to the labora-tory before the onset of the experimental procedure.

Prior to each six-trait sequence, the attitude-report instructions ap-peared on the screen informing participants to either (a) respond accu-rately whenever they felt negatively (neutrally) or (b) respond positivelywhenever they felt negatively (neutrally). Participants then initiated thesequence by pressing a key on a keypad that was located next to theirright hands. One second after the participant pressed a key, the first ofthe six trait adjectives appeared on the screen. Each trait was presentedfor 1,000 ms, and the interstimulus interval was 1,900 ms. Nineteenhundred milliseconds following the offset of the sixth trait, the attitude-report instructions for the next sequence appeared on the screen.

Twenty-four different types of sequences were used in the experiment.As can be seen in Table 1, participants were instructed to respond accu-rately when they felt negatively (neutrally) prior to 12 of the sequencetypes and to respond positively when they felt negatively (neutrally)prior to 12 of the sequence types. Each of these 24 sequence types waspresented 10 times during the experiment, and the order of these 240six-trait sequences was randomly determined for each participant. The

1 Analyses reported in the text were conducted collapsing across gen-der because initial analyses of Studies 1 and 2 revealed no significantmain effect or interaction involving gender.

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Table 1Types of Six-Word Sequences Used in Study 1

Stimulus position Response to target stimulus

Sequence type

Report Attitudes Accurately1) Positive in positive2) Positive in positive3) Positive in positive4) Positive in positive

5) Neutral in positive6) Neutral in positive7) Neutral in positive8) Neutral in positive

9) Negative in positive10) Negative in positive11) Negative in positive12) Negative in positive

Misreport Attitudes13) Positive in positive14) Positive in positive15) Positive in positive16) Positive in positive

17) Neutral in positive18) Neutral in positive19) Neutral in positive20) Neutral in positive

21) Negative in positive22) Negative in positive23) Negative in positive24) Negative in positive

1

PPPP

PPPP

PPPP

PPPP

PPPP

PPPP

2

PPPP

PPPP

PPPP

PPPP

PPPP

PPPP

3

PPPP

PPP

<t>PPPN

PPPP

PPP4>pPpN

4

PPPn

PP

P

PPNn

PPPn

PP

P

PPNn

5

PP

<t>P

P

•©-'

<t>n

PN

<t>P

PP

<t>P

P

<t><t>n

PN

<t>P

6

PPn

<t><t>P<t>P

N

<t>nP

PPn

•©-

4>n0P

N4>nP

Neutral focus

positivepositivepositivepositive

neutralneutralneutralneutral

negativenegativenegativenegative




Negative focus







Note, p = a stimulus position in which positive traits were presented; 0 = a stimulus position in whichneutral traits were presented; n = a stimulus position in which negative traits were presented. Each sequencetype was presented 10 times. For the first 12 sequence types, participants were instructed to respond accu-rately when they felt positively, neutrally, or negatively. For the second 12 sequence types, participants wereinstructed to respond positively when they felt negatively (neutrally) but to respond accurately when theyfelt positively or neutrally (negatively). Within each sequence type, EEG was recorded to an evaluativelyconsistent, moderately inconsistent, or highly inconsistent target trait that was located in either the third,fourth, fifth, or sixth stimulus position; these stimuli are designated by boldface capital letters. To increasethe likelihood that participants would attend to all of the stimuli within each sequence and across the 240sequences, (a) the 240 sequences were randomly ordered for each participant, (b) target stimuli were pre-sented in differing stimulus positions, and (c) multiple inconsistent traits were presented in many of thesequence types.

trait adjectives that appeared at the six stimulus positions within each ofthe 240 sequences were randomly selected from the appropriate valencecategory. Trait adjectives were selected in blocks without replacementuntil all of the traits within a valence category had been selected. Thatis, all of the traits within each valence category were used once beforeany were presented twice, all were used twice before any were presentedfor a third time, and so on.

As illustrated in Table 1, three types of target stimuli were used: (a)positive traits that were preceded by all positive traits (i.e., evaluativelyconsistent), (b) neutral traits that were preceded by all positive traits(i.e., moderately evaluatively inconsistent), and (c) negative traits thatwere preceded by all positive traits (i.e., highly evaluativelyinconsistent). The positive context of each sequence was established bypresenting either two, three, four, or five positive traits before the targetstimulus to prevent participants from anticipating whether or where aninconsistent stimulus would appear within a sequence.2 As illustrated

in Table 1, positive, negative, and /or neutral trait adjectives were pre-sented after the target stimulus in sequences in which the target stimuluswas not the sixth stimulus. This was done to increase the number ofnegative and neutral traits that could be used in the study and to mini-mize the chance that participants would fall into a response set of sim-ply expressing positive attitudes.

Data acquisition and reduction. Electroencephalographic activitywas measured over three midline (Fz, Cz, and Pz) scalp locations ofthe international 10-20 system (Jasper, 1958) and referenced to linked

2 The position of the target stimulus was not included in the analysesbecause it has not been found to alter reliably the amplitude or latencyof the LPP (Crites, 1991) and because more reliable LPP amplitudesand latencies are obtained by averaging across this factor.


mastoids.3 Because eye movements and blinks can produce artifacts inthe EEG, vertical electroculographic (VEOG) activity was recordedfrom the right eye by supra- and infraorbital electrodes. A ground elec-trode was placed on the center of the forehead. All electrical recordingswere made using 4 mm Ag/AgCl electrodes. Prior to electrode attach-ment, the electrodes were filled with a high conductivity gel, and therecording sites were cleaned with alcohol and abraded using Omni Prep.All interelectrode impedances were under 10 Kohms. Scalp electrodeswere attached using the double-collar technique (Fein, Frosch, & Bor-roni, 1975). Electroencephalographic and VEOG signals were ampli-fied by Grass Model 12A5 amplifiers with a bandpass of .1-30.0 Hz(6-dB roll-off) and digitized at 481 Hz. Electroencephalographic andVEOG activity were recorded for 2,128 ms to a single target stimuluswithin each sequence; each recording epoch began 128 ms before theonset of a target stimulus, continued through the 1,000-ms stimuluspresentation, and extended 1,000 ms after the offset of the targetstimulus.

A number of steps were taken to ensure the integrity of the bioelec-trical data. We first examined the EEG and VEOG recordings fromeach of the 240 presentations of target stimuli, using software to deter-mine whether any amplifier had been saturated. Whenever saturationoccurred, all of the data for that target stimulus were excluded fromfurther analyses. Because ocular movements can manifest in the EEGrecordings and distort averaged waveforms, we applied a regression pro-cedure for removing ocular artifacts to the EEG recordings (Semlitsch,Anderer, Schuster, & Presslich, 1986). We then examined visually theEEG and VEOG recordings to each target stimulus, and if any ocularor other (e.g., electrocardiographic, EMG) artifact was detected in anyof the EEG recordings, all of the EEG data for that trial sequence wereexcluded from further analyses.

Because electrocranial activity that is unrelated to a stimulus (i.e.,spontaneous EEG activity) is large compared with components of theERP and thus tends to obscure components of the ERP on any singlepresentation of a stimulus, multiple recordings must be aggregated toquantify components of the ERP. (ERP components can be distin-guished from spontaneous EEG activity by aggregating multiple record-ings because ERP components, but not spontaneous EEG activity,within each recording are time-locked to an identifiable event.) Beforethe EEG recordings were aggregated, each EEG recording was baselinecorrected to the mean of its 128-ms prestimulus period. We then aver-aged the EEG recordings over each site for each participant separatelyfor positive, neutral, and negative target stimuli within the accurate at-titude-report and attitude-misreport sequences.4 Thus, 18 averagedwaveforms were created for each participant (i.e., 3 scalp sites X 3 stim-ulus valences X 2 attitude-report instructions). These averaged wave-forms were then digitally low-pass filtered at 10 Hz (Cacioppo et al.,1993). To quantify the LPP of the ERP, the amplitude and latency ofthe largest positive potential at Pz between 400 and 900 ms followingstimulus onset was identified and recorded, and the amplitude and la-tency of the largest positive potential at Cz and Fz that was within ± 100ms of the largest potential at Pz were then recorded.5

Results

Behavioral responses to target stimuli. To assess whether the at-titude-report instruction altered participants' behavioral responsesto the target traits, we subjected the number of target stimuli thatwere reported as positive to a 2 (focus: report negative traits as pos-itive or accurately vs. report neutral traits as positive or accurately)X 3 (trait valence: positive, neutral, or negative) X 2 (attitude-reportinstruction: accurately report valence of negative or neutral traitsvs. report negative or neutral traits as positive) multivariate analysisof variance (MANOVA), with the first variable manipulated be-

tween subjects.6 As expected, the three-way interaction among fo-cus, trait valence, and attitude-report instruction was significant,F(2,19) = 55.43, p < . 0 1 . As can be seen in Figure 1, instructionsto report negative traits as positive selectively increased the numberof negative traits that were reported as positive, whereas instructionsto report neutral traits as positive selectively increased the numberof neutral traits that were reported as positive. Thus, the attitude-report instruction to report accurately versus misreport negative orneutral attitudes as positive altered participants' behavioral re-sponses to these negative or neutral traits.

Amplitude of the LPP to target stimuli. We subjected theamplitude of the LPP over the midline scalp sites to a 2 (focus:report negative traits as positive or accurately vs. report neutraltraits as positive or accurately) X 3 (sagittal scalp location: Fz,Cz, or Pz) X 3 (evaluative inconsistency: consistent positivetrait, moderately inconsistent neutral trait, or highly inconsis-tent negative trait) X 2 (attitude-report instruction: accuratelyreport valence of negative or neutral traits vs. report negativeor neutral traits as positive) MANOVA, with the first variablemanipulated between subjects. As expected, results revealed asignificant main effect for the evaluative inconsistency of thetarget trait, F(2, 19)= 11.66, p< .01. In accord with the find-ings of Cacioppo et al. (1993, 1994), negative traits presentedin a positive-trait context (highly evaluatively inconsistent)evoked a larger amplitude LPP (M = 8.93 /J.V) than positivetraits (M = 4.88 fiV) presented in a positive-trait context(evaluatively consistent) (/? < .05). Furthermore, the LPPevoked by neutral traits presented in a positive-trait context (M= 7.07 jiV) was significantly smaller than that evoked by nega-tive traits presented in a positive-trait context and significantlylarger than the LPP evoked by positive traits presented in a pos-itive-trait context (ps < .05). These significant differences be-

3 EEG was also recorded from six lateral scalp locations (F3, F4, C3,C4, P3, and P4) for the purpose of establishing a database for topo-graphical analyses; data from these sites are not included in the presentanalyses and will not be discussed further.

4 EEG recordings were included in the averaged waveforms regardlessof a participant's specific attitudinal response to increase the number ofEEG recordings that were included in the waveforms and, therefore, thereliability of the waveforms. To assess whether including these record-ings influenced the results, we performed analyses on averaged wave-forms that included only correct behavioral responses. In all cases, thepattern of results was the same as those reported in the text.

5 The largest potential at Pz was selected because the amplitude of theP300 component is generally greatest at Pz (Fabiani et al., 1987), andthe amplitude of the LPP observed by Cacioppo et al. (1993,1994) waslargest over Pz. The values at the other scalp sites were restricted towithin + or -100 ms of Pz so we would have more confidence that thesame psychological process and neural generators were responsible forthe potential that was quantified at each scalp site. To assess whetherimposing this restriction diminished the values at the other scalp sites,we conducted analyses using the largest point at each electrode site (i.e.,rather than the largest point to fall within 100 ms of Pz). In all cases,the pattern of results were the same as those reported in the text.

6 Because violations of the sphericity assumption are prevalent forrepeated measures of physiological responses, we used multivariate teststatistics in all analyses to protect against the increased probability ofType I errors that occur when univariate tests are performed on datathat violate the sphericity assumption.


Negative Focus

•5 40

3 35-

S 30 -Hf» 25-

» 2

f 1

"a

3 10 -

II

40

35

30

25

20

15

10

5

I

• Report Positive, Neutral, &Negative Accurately

D Report Positive & NeutralAccurately and MisreportNegative

APositive Neutral

Trait Valence

Neutral Focus

Negative

O Report Positive, Neutral, &| Negative Accurately

D Report Positive & NegativeAccurately and MisreportNeutral

Positive NeutralTrait Valence

Negative

Figure 1. Behavioral responses to target stimuli for participants in thenegative- and neutral-focus conditions of Study 1. The graph depicts thefrequency with which positive, neutral, and negative target stimuli wereidentified as positive during (a) sequences in which participants re-ported accurately all of their attitudes and (b) sequences in which par-ticipants misreported negative or neutral attitudes as positive.

tween the amplitude of the LPP evoked by negative, neutral,and positive traits are consistent with Cacioppo et al.'s (1994)results, suggesting that the amplitude of the LPP increases asthe mismatch increases between the evaluative categorizationof a stimulus and the expected evaluative significance based oncontextual stimuli (see Figures 2 and 3).

The expected main effect involving the scalp distribution ofthe LPP was also obtained as the amplitude of the LPP de-creased across the scalp from Pz to Fz (Mpj = 9.91 pV; M& =7.73 MV; MFZ = 3.25 jtV), F(2, 19) = 46.13, p < .01 (see Fig-ures 2 and 3). In addition, there was a significant Evaluative

Inconsistency X Sagittal interaction, F(4, 17) = 6.72, p < .01.Pairwise comparisons revealed that the amplitude of the LPPevoked by positive, neutral, and negative target traits were allsignificantly different from one another at Pz and Cz and thatthe amplitude of the LPP evoked by positive target traitsdiffered from those evoked by neutral and negative target traitsat Fz (ps < .05). Thus, and as expected, the effects of evaluativeinconsistency on the amplitude of the LPP were most apparentat the centroparietal regions of the scalp (i.e., Cz and Pz). Fi-nally, no other main effect or interaction was significant, sug-gesting that the attitude-report instruction had no effect on theamplitude or scalp distribution of the LPP.

Specific contrasts examining effect of attitude-report instruc-tions on behavioral responses and the amplitude of the LPP.The omnibus analyses on the amplitude of the LPP and the be-havioral responses to target traits support our hypothesis thatinstructions to misreport negative or neutral attitudes as posi-tive alter individuals' behavioral responses but do not affect theamplitude or scalp distribution of the LPP. To more thoroughlyexamine the effect of instructions to report accurately or reportpositively negative or neutral traits on the amplitude of the LPPevoked by, and the behavioral responses to, negative or neutraltraits, we conducted a series of specific contrasts. We performedthe first set of contrasts on data from participants in the nega-tive-focus condition to compare (a) the behavioral responsesand (b) the LPP amplitudes to negative traits from sequencesin which participants were instructed to report accurately withthe parallel results from sequences in which participants wereinstructed to misreport negative traits as positive. These twocontrasts revealed that instructions to report negative traits ac-curately versus positively significantly altered participants' atti-tude reports (Ms = 3.55 and 31.27), F( 1, 10) = 179.10, p <.01 (see Figure 1) but did not significantly affect the amplitudeoftheLPP(Ms = 10.31 MV and 7.09/tV),F(l, 10) = 4.60, ns(see Figure 2).

We then performed parallel analyses on data from partici-pants in the neutral-focus condition. These two contrasts re-vealed that instructions to report neutral traits accurately ver-sus positively significantly altered participants attitude reports(Ms = 10.64 and24.55), F{ 1,10) = 34.16, p < .01 (see Figure1), but did not significantly affect the amplitude of the LPP (Ms= 8.55 fiV and 8.58 /xV, F< 1; see Figure 3). Thus, the findingsfrom these two sets of contrasts suggest that the amplitude ofthe LPP to evaluatively inconsistent stimuli is not significantlyreduced when participants misreport the valence of evaluativelyinconsistent stimuli.

We then conducted two sets of contrasts to determine if neg-ative or neutral (i.e., evaluatively inconsistent) traits that werereported as positive evoked a larger amplitude LPP than posi-tive (i.e., evaluatively consistent) traits. We performed the firstset of contrasts on data from participants in the negative-focuscondition to compare (a) the LPP amplitudes and (b) the be-havioral responses to negative traits from sequences in whichparticipants were instructed to misreport negative traits as pos-itive with parallel results to positive traits in the analogous se-quence types. As expected, negative target traits presented in apositive-trait context evoked a larger LPP (M = 7.09 j«V) thanpositive target traits (M = 2.39 /tV) presented in a positive-trait


Report Accurately

Pz

Misreport Negative

Pz

600 1200 600 1200

600 1200 600 1200

Fz

600 1200 600 1200

Positive Neutral Negative

Figure 2. Averaged event-related brain potential waveforms to target stimuli for participants in the nega-tive-focus condition of Study 1. The three graphs on the left depict the averaged waveforms at Pz, Cz, andFz (from top to bottom, respectively) associated with positive, neutral, and negative target stimuli in se-quences in which participants were instructed to report accurately positive, neutral, and negative attitudes.The three graphs on the right depict the averaged waveforms at Pz, Cz, and Fz (from top to bottom,respectively) associated with positive, neutral, and negative target stimuli in sequences in which participantswere instructed to report accurately positive and neutral attitudes but to misreport negative attitudes. Thelate positive potential is the positive (downward) peak that peaks at approximately 500 to 600 ms.

context, F( 1,10) = 10.62, p < .01 (see Figure 2), even thoughboth positive (M = 31.82) and negative (M = 31.27) targettraits were equally likely to be reported as positive, F( 1, 10) <1 (see Figure 1).

Again, we performed parallel analyses on data from partici-pants in the neutral-focus condition. As expected, results re-vealed that neutral target traits presented in a positive-traitcontext evoked a larger LPP {M = 8.58 pV) than positive targettraits (M = 6.15 /iV) presented in a positive-trait context, F( 1,

10) = 5.56, p < .05 (see Figure 3). The number of positivetarget traits that were reported as positive (M = 37.36), how-ever, was larger than the number of neutral target traits that werereported as positive (M = 24.55), F( 1, 10) = 125.83, p< .01(see Figure 1).

Discussion

In this study, a distinction was made between the evaluativejudgment (categorization) and the response components un-


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Figure 3. Averaged event-related brain potential waveforms to target stimuli for participants in the neu-tral-focus condition of Study 1. The three graphs on the left depict the averaged waveforms at Pz, Cz, andFz (from top to bottom, respectively) associated with positive, neutral, and negative target stimuli in se-quences in which participants were instructed to report accurately positive, neutral, and negative attitudes.The three graphs on the right depict the averaged waveforms at Pz, Cz, and Fz (from top to bottom,respectively) associated with positive, neutral, and negative target stimuli in sequences in which participantswere instructed to report accurately positive and negative attitudes but to misreport neutral attitudes. Thelate positive potential is the positive (downward) peak that peaks at approximately 500 to 600 ms.

derlying an attitude. The participants' task was to categorizeeach stimulus in a six-stimulus sequence as either positive, neu-tral, or negative and to either report accurately or misreport thevalence of certain evaluatively inconsistent stimuli. As Caci-oppo et al. (1993,1994) found, the LPP evoked by evaluativelyinconsistent stimuli was larger than the LPP evoked by evalua-tively consistent stimuli. This study extends our earlier findingsby showing that the amplitude of the LPP varies as a functionof evaluative categorization rather than attitude reports. In-

structions to misreport the vatence of stimuli led to the in-structed changes in attitude report, but these attitude-report in-structions did not significantly change the amplitude or thescalp distribution of the LPP to these stimuli. Notably, analysesrevealed that (a) the amplitude of the LPP to evaluatively in-consistent negative and neutral stimuli was not diminishedwhen these stimuli were reported as positive (i.e., evaluativelyconsistent), and (b) evaluatively inconsistent negative and neu-tral stimuli evoked a larger amplitude LPP than evaluatively


consistent positive stimuli even when the negative and neutralstimuli were reported as positive. Thus, the present study ex-tends our prior research by demonstrating that the amplitudeof the LPP evoked by a stimulus and an individual's attitudereport to that stimulus can be functionally separated.

The primary purpose of including three distinct categories ofevaluative stimuli in the present experiment was to ensure thateach stimulus was categorized along an evaluative dimensioneven when participants misreported their attitudes. The use ofpositive, neutral, and negative stimuli, however, also allowedCacioppo et al.'s (1994) findings to be replicated. In Cacioppoet al.'s (1994) study, participants were asked to dichotomouslycategorize stimuli as either positive or negative, and evaluativeinconsistency was varied by embedding very positive, moder-ately positive, moderately negative, and very negative stimuliin sequences containing predominantly very positive stimuli;results revealed that the amplitude of the LPP varied as a func-tion of the degree of the mismatch between an evaluative cate-gorization of a stimulus and the expected evaluative significancebased on contextual stimuli. Consistent with Cacioppo et al.'s(1994) results, stimuli that were highly evaluatively inconsis-tent evoked a larger amplitude LPP than did stimuli that weremoderately evaluatively inconsistent, which evoked a larger am-plitude LPP than did stimuli that were evaluatively consistent.

In this study, we varied evaluative inconsistency by establish-ing a positive context in each sequence and then embeddingpositive, neutral, and negative target traits in the sequences. Anadvantage of using only a single evaluative context, as opposedto using both positive and negative contexts, is that each se-quence type can be presented twice the number of times,thereby improving the reliability of the ERP after averaging. Be-cause negative attitudes toward individuals may be particularlylikely to be distorted in self-report measures, we used a positive,as opposed to a negative, context in Study 1 to investigate theeffects of an individual expressing a positive attitude toward adisliked individual on the enhancement of the LPP amplitude.Cumulative research, however, suggests that negative eventshave a larger impact generally on individuals than positiveevents (Cacioppo & Berntson, 1994; Taylor, 1991). Eventhough Cacioppo et al. (1993) found no evidence that this neg-ativity bias affects the LPP of the ERP, we nevertheless con-ducted a second experiment to investigate the effects of an indi-vidual expressing a negative attitude toward a liked individualon the enhancement of the LPP amplitude.

Study 2

MethodOverview. To conceptually replicate Study 1 and to examine the

effects of misreporting evaluatively inconsistent positive attitudes on theenhancement of the LPP amplitude, we used a negative stimuluscontext in Study 2. During half of the experimental sequences, partici-pants were instructed to report accurately their attitudes toward allthree categories of evaluative stimuli. During the remaining sequences,half of the participants were instructed to report their neutral attitudesas being negative and report accurately positive and negative attitudes,whereas half of the participants were instructed to report their positiveattitudes as being negative and report accurately neutral and negativeattitudes.

Although Study 1 revealed that instructions to misreport the valenceof negative or neutral traits altered participants' behavioral responses tothose traits, participants in Study 1 were unexpectedly inaccurate atcorrectly identifying neutral traits. Neutral traits were frequently re-ported as either positive or negative even when participants were in-structed to report accurately the valence of neutral traits, thus suggest-ing that our consensual "neutral" traits may not have always triggeredneutral attitudes. Thus, in an attempt to ensure that all of the neutraltraits elicited neutral attitudes, each participant in Study 2 selected a setof traits that he or she personally believed to be neutral prior to theexperiment.

Participants. Thirty Introductory Psychology students (15 femaleand 15 male) at Ohio State University participated in the experiment inpartial fulfillment of a course requirement. All of the participants wereright-handed and in good health. We randomly assigned 15 participantsto the positive-focus condition, in which they periodically misreportedthe valence of positive attitudes, and randomly assigned 15 participantsto the neutral-focus condition, in which they periodically misreportedthe valence of neutral attitudes.

Stimulus materials. As in Study 1, we used three categories of atti-tudinal stimuli in this study. Unlike in Study 1, however, a short se-quence of negative trait adjectives always preceded the positive, neutral,and negative target traits to which EEG was recorded. Thus, a greaternumber of negative trait adjectives was needed to equate for the numberof times that each trait adjective was presented; a combination of 52negative, 10 neutral, and 10 positive trait adjectives allowed each traitto be presented an equal number of times during the course of the ex-periment. The pool of negative traits were the 52 most negatively ratedadjectives from Anderson's (1968) list of trait adjectives, and the poolof positive traits consisted of the 10 most positively rated adjectives.Because participants often incorrectly identified the neutral traits aseither positive or negative in Study 1, each participant selected a set of10 traits that he or she personally believed to be neutral from a list of 55traits. The 55 traits were adjectives whose mean likableness ratingsranged from 3.34 (i.e., cautious) to 2.57 (i.e., eccentric) on Anderson's(1968) 7-point (0-6) scale. Thus, this list of 55 traits included traitadjectives whose mean likableness ratings fell between the scale mid-point of Anderson's scale (i.e., 3.00) and the median likableness rating(i.e., 2.66) of the 555 trait adjectives.

Procedure and data reduction. Except for the following fourchanges, the experimental procedure and data acquisition and reduc-tion procedures were identical to those used in Study 1. First, partici-pants were told that the purpose of this experiment was to determinewhether people's brain activity revealed their positive (neutral) atti-tudes toward another individual even if they reported that their attitudewas negative. Second, before the electrodes were attached, participantsidentified 10 traits that described individuals toward whom they wouldfeel neutrally. Third, during the sequences in which participants misre-ported their positive (neutral) attitudes, 15 participants reported theirneutral attitudes as being negative (but accurately reported positive andnegative attitudes), and 15 participants reported their positive attitudesas being negative (but accurately reported neutral and negativeattitudes). Fourth, an evaluatively negative context was establishedwithin each sequence by presenting either two, three, four, or five nega-tive traits before the target stimulus. As illustrated in Table 2, three typesof target stimuli were used: (a) negative traits that were preceded by allnegative traits (i.e., evaluatively consistent stimulus), (b) neutral traitsthat were preceded by all negative traits (i.e., moderately evaluativelyinconsistent stimulus), and (c) positive traits that were preceded by allnegative traits (i.e., highly evaluatively inconsistent stimulus).

Results

Behavioral responses to target stimuli. To assess whether theattitude-report instruction altered participants' attitude re-


Table 2Types of Six- Word Sequences Used in Study 2

Stimulus position Response to target stimulus

Sequence type

Report Attitudes Accurately1) Negative in negative2) Negative in negative3) Negative in negative4) Negative in negative

5) Neutral in negative6) Neutral in negative7) Neutral in negative8) Neutral in negative

9) Positive in negative10) Positive in negative11) Positive in negative12) Positive in negative

Misreport Attitudes13) Negative in negative14) Negative in negative15) Negative in negative16) Negative in negative

17) Neutral in negative18) Neutral in negative19) Neutral in negative20) Neutral in negative

21) Positive in negative22) Positive in negative23) Positive in negative24) Positive in negative

1

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Neutral focus







Positivefocus







Note, n = a stimulus position in which negative traits were presented; 0 = a stimulus position in whichneutral traits were presented; p = a stimulus position in which positive traits were presented. Each sequencetype was presented 10 times. For the first 12 sequence types, participants were instructed to respond accu-rately when they felt negatively, neutrally, or positively. For the second 12 sequence types, participants wereinstructed to respond negatively when they felt positively (neutrally) but to respond accurately when theyfelt negatively or neutrally (positively). Within each sequence type, EEG was recorded to an evaluativelyconsistent, moderately inconsistent, or highly inconsistent target trait that was located in either the third,fourth, fifth, or sixth stimulus position; these stimuli are designated by boldface capital letters. To increasethe likelihood that participants would attend to all of the stimuli within each sequence and across the 240sequences, (a) the 240 sequences were randomly ordered for each participant, (b) target stimuli were pre-sented in differing stimulus positions, and (c) multiple inconsistent traits were presented in many of thesequence types.

ports, we subjected the number of target stimuli that were re-ported as negative to a 2 (focus: report positive traits as negativeor accurately vs. report neutral traits as negative or accurately)X 3 (trait valence: negative, neutral, or positive) X 2 (attitude-report instruction: accurately report valence of positive or neu-tral traits vs. report positive or neutral traits as negative)MANO\A, with the first variable manipulated between sub-jects.7 As expected, the three-way interaction among focus, traitvalence, and attitude-report instruction was significant, F(2,26) = 108.98, p < .01. As can be seen in Figure 4, instructionsto report positive traits as negative selectively increased thenumber of positive traits that were reported as negative,whereas instructions to report neutral traits as negative selec-tively increased the number of neutral traits that were reported

as negative. Thus, as in Study 1, the attitude-report instructionto report accurately versus misreport positive or neutral atti-tudes as negative altered participants' behavioral responses tothese positive or neutral traits.

Amplitude of the LPP to target stimuli. We subjected theamplitude of the LPP over the midline scalp sites to a 2 (focus:report positive traits as negative or accurately vs. report neutraltraits as negative or accurately) X 3 (sagittal scalp location: Fz,Cz, or Pz) X 3 (evaluative inconsistency: evaluatively consistent

7 Because of technical problems, behavioral responses from 1 partic-ipant in the negative-focus condition were unavailable for analyses.Thus, analyses on the behavioral responses included data from only 29of the 30 participants.


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Figure 4. Behavioral responses to target stimuli for participants in thepositive- and neutral-focus conditions of Study 2. The graph depicts thefrequency with which negative, neutral, and positive target stimuli wereidentified as negative during (a) sequences in which participants re-ported accurately all of their attitudes asd (b) sequences in which par-ticipants misreported positive or neutral attitudes as negative.

negative trait, moderately inconsistent neutral trait, or highlyinconsistent positive trait) X 2 (attitude-report instruction: ac-curately report valence of positive or neutral traits vs. reportpositive or neutral traits as negative) MANOY\, with the firstvariable manipulated between subjects. As expected, results re-vealed a significant main effect for the evaluative inconsistencyof the target trait, F(2,27) = 15.48, p< .01. In accord with theresults of Study 1, positive traits presented in a negative-traitcontext (highly evaluatively inconsistent) evoked a larger am-plitude LPP (M = 6.70 ^V) than negative traits (M = 4.27 nV)presented in a negative-trait context (evaluatively consistent; p

< .05); and neutral traits presented in a negative-trait context(moderately evaluatively inconsistent) evoked a larger ampli-tude LPP (M = 7.60 /iV) than negative traits presented in anegative-trait context (p < .05, see Figures 5 and 6). There wasno significant difference, however, between the amplitude of theLPP evoked by positive traits presented in a negative-traitcontext and neutral traits presented in a negative-trait context.

The expected main effect involving the scalp distribution ofthe LPP was also obtained as the amplitude of the LPP de-creased across the scalp from Pz to Fz (M& = 7.57 *iV; MCl =7.20 MV; MFI = 3.80 nV), F(2, 27) = 33.75, p < .01 (see Fig-ures 5 and 6). This sagittal main effect was qualified by a FocusX Sagittal interaction, F(2,27) = 5.53,/> < .05, which revealedthat the amplitude of the LPP decreased from Pz to Cz for par-ticipants in the positive-focus condition (p < .05) but not forparticipants in the neutral-focus condition. In addition, and aswas found in Study 1, there was a significant Evaluative Incon-sistency X Sagittal interaction, F(4,25) = 5.24, p < .01, whichoccurred because the difference between the amplitudes of theLPP evoked by evaluatively inconsistent (i.e., positive andneutral) and evaluatively consistent (i.e., negative) traits at Pzand Cz was larger than at Fz. Thus, as in Study 1, the effects ofevaluative inconsistency on the amplitude of the LPP were mostapparent at the centroparietal regions of the scalp.

Finally, there was an attitude-report instruction main effect,which revealed that the amplitude of the LPP elicited duringsequences in which participants accurately reported the valenceof all traits (M = 6.61 /xV) was larger than the amplitude of theLPP elicited during sequences in which participants reportedthat positive or neutral traits were negative (M = 5.77 /tV),F( 1, 28) = 6.11, p < .05. Importantly, there were no interac-tions involving attitude-report instruction, suggesting that theamplitudes of the LPP evoked by negative, neutral, and positivetraits were all reduced in sequences in which participants re-ported that positive or neutral traits were negative. No othermain effect or interaction was significant.

Specific contrasts examining effect of attitude-report instruc-tions on behavioral responses and the amplitude of the LPP. Asin Study 1, we conducted a series of specific contrasts to morethoroughly examine the effect of attitude-report instructions onthe amplitude of the LPP and the behavioral responses. The firstset of contrasts was performed on data from participants in thepositive-focus condition to compare (a) the behavioral re-sponses and (b) the LPP amplitudes to positive traits from se-quences in which participants were instructed to report accu-rately with the parallel results from sequences in which partici-pants were instructed to misreport positive traits as negative.These two contrasts revealed that instructions to report positivetraits accurately versus negatively significantly altered partici-pants' attitude reports (Ms = 3.71 and 32.14), F(l, 13) =193.18, p < .01 (see Figure 4), but did not significantly affectthe amplitude of the LPP (Ms = 6.46 /iV and 5.93 /tV, F < 1;see Figure 5).

We then performed parallel analyses on data from partici-pants in the neutral-focus condition. These two contrasts re-vealed that instructions to report neutral traits accurately ver-sus negatively significantly altered participants' attitude reports(Ms = 6.40and 33.53), F( 1, 14) = 123.32,p< .01 (seeFigure


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Figure 5. Averaged event-related brain potential waveforms to target stimuli for participants in the posi-tive-focus condition of Study 2. The three graphs on the left depict the averaged waveforms at Pz, Cz, andFz (from top to bottom, respectively) associated with negative, neutral, and positive target stimuli in se-quences in which participants were instructed to report accurately negative, neutral, and positive attitudes.The three graphs on the right depict the averaged waveforms at Pz, Cz, and Fz (from top to bottom,respectively) associated with negative, neutral, and positive target stimuli in sequences in which participantswere instructed to report accurately negative and neutral attitudes but to misreport positive attitudes. Thelate positive potential is the positive (downward) peak that peaks at approximately 500 to 600 ms.

4) but did not significantly affect the amplitude of the LPP (Ms= 8.82 j*V and 7.56 (iV), F( 1, 14) = 2.23, ns (see Figure 6).Thus, the findings from these two sets of contrasts are consistentwith the findings of Study 1 and suggest that the amplitude ofthe LPP to evaluatively inconsistent stimuli is not significantlyreduced when participants misreport the valence of evaluativelyinconsistent stimuli.

As in Study 1, we conducted two sets of contrasts to deter-mine if positive or neutral (i.e., evaluatively inconsistent) traits

that were reported as negative evoked a larger amplitude LPPthan negative (i.e., evaluatively consistent) traits. We performedthe first set of contrasts on data from participants in the posi-tive-focus condition to compare (a) the LPP amplitudes and(b) the behavioral responses to positive traits from sequences inwhich participants were instructed to misreport positive traitsas negative with parallel results to negative traits in the analo-gous sequence types. As expected, positive target traits pre-sented in a negative-trait context evoked a larger LPP (M = 5.93


Report Accurately

Pz

Misreport Neutral

Pz

600 1200 600 1200

600 1200 1200

600 1200 600 1200

Negative Neutral Positive

Figure 6. Averaged event-related brain potential waveforms to target stimuli for participants in the neu-tral-focus condition of Study 2. The three graphs on the left depict the averaged waveforms at Pz, Cz, andFz (from top to bottom, respectively) associated with negative, neutral, and positive target stimuli in se-quences in which participants were instructed to report accurately negative, neutral, and positive attitudes.The three graphs on the right depict the averaged waveforms at Pz, Cz, and Fz (from top to bottom,respectively) associated with negative, neutral, and positive target stimuli in sequences in which participantswere instructed to report accurately positive and neutral attitudes but to misreport neutral attitudes. Thelate positive potential is the positive (downward) peak that peaks at approximately 500 to 600 ms.

than negative target traits (M = 3.64 /xV) presented in anegative-trait context, F{ 1, 14) = 4.94, p < .05 (see Figure 5),even though both positive (M = 32.14) and negative (M =33.21) target traits were equally likely to be reported as negative( F < 1; see Figure 4).

We then performed parallel analyses on data from participants inthe neutral-focus condition. As expected, results revealed that neu-tral target traits presented in a negative-trait context evoked a largerLPP (M = 7.56 nV) than negative target traits (M = 4.31

presented in a negative-trait context, F( 1,14) = 7.76, p < .05 (seeFigure 6). The number of negative target traits that were reportedas negative (M = 38.67), however, was larger than the number ofneutral target traits that were reported as negative (M = 33.53),F ( l , 14)= 18.71,p<.01(seeFigure4).

DiscussionThe findings of this study replicate our prior research

(Cacioppo et al., 1993, 1994), as well as Study 1, in demon-


strating that, when individuals evaluatively categorize stimuli,evaluatively inconsistent stimuli evoke a larger amplitude LPPthan do evaluatively consistent stimuli. Importantly, and as wasfound in Study 1, the amplitude of the LPP evoked by a stimu-lus and an individual's attitude report regarding that stimuluscan be functionally separated. In a conceptual replication of thefindings of Study 1, analyses revealed that (a) the amplitude ofthe LPP to evaluatively inconsistent positive and neutral stimuliwas not diminished when these stimuli were reported as nega-tive (i.e., evaluatively consistent), and (b) evaluatively inconsis-tent positive and neutral stimuli evoked a larger amplitude LPPthan evaluatively consistent negative stimuli, even when the pos-itive and neutral stimuli were reported as negative. Thus, in-structions to misreport the valence of stimuli led to the in-structed changes in attitude report, but these attitude-report in-structions did not significantly change the amplitude or thescalp distribution of the LPP evoked by these stimuli.

Unlike the findings of Cacioppo et al. (1994) and Study 1, theLPP evoked by highly evaluatively inconsistent stimuli was notsignificantly larger than the LPP evoked by moderately evalua-tively inconsistent stimuli. One potential explanation for thesedifferent findings is that participants in this study, but not par-ticipants in Study 1, were exposed to and selected the neutraltraits prior to the ERP task. The amplitude of the LPP to theneutral traits in this study may have increased, relative to theamplitude of the LPP to the previously unseen positive and neg-ative traits, because of this prior exposure. Support for this ex-planation comes from a study by Bentin, Moscovitch, and Heth(1992), in which participants were exposed to a set of stimuliprior to participating in an ERP experiment. These items werethen presented along with new items while participants per-formed either an explicit memory task in which they catego-rized each stimulus as either "old" or "new" or an implicitmemory task in which they either semantically or lexically cat-egorized each stimulus. Bentin et al. found that, in both theexplicit and implicit memory tasks, a larger amplitude P300was evoked by stimuli that participants had seen earlier as com-pared with stimuli that participants had not seen earlier. Thus,prior exposure to the neutral, but not the positive or negative,traits may have selectively enhanced the amplitude of the LPPto the neutral traits.

A second potential explanation for the different findings ofStudy 1 and Study 2 regarding the amplitude of the LPP tomoderately and highly inconsistent stimuli is that the impact ofa positive stimulus in a sequence of negative stimuli may besmaller than the impact of a negative stimulus in a sequence ofpositive stimuli. As discussed above, cumulative research sug-gests that negative events have a larger impact generally on indi-viduals than positive events (Cacioppo & Berntson, 1994; Tay-lor, 1991). In this study, positive stimuli were evaluatively in-consistent with the negative contextual stimuli, whereas inStudy 1 and in Cacioppo et al.'s (1994) study, negative stimuliwere evaluatively inconsistent with the positive contextual stim-uli. Although speculative at this juncture, the differences in theLPP amplitude to the evaluatively inconsistent negative andpositive traits in Studies 1 and 2, respectively, may reflect a sen-sitivity to this negativity bias. Inspection of the LPP amplitudesacross these two studies indicates that an occasional negative

trait in a positive context evokes a larger LPP (M = 8.93 n)than an occasional positive trait in a negative context (M = 6.70ttY). In contrast, the occasional neutral trait in positive andnegative contexts evoked comparable amplitudes (Ms = 7.07and 7.60 jiV, respectively), as did the frequent positive trait in apositive context and the frequent negative trait in the negativecontext (Ms = 4.88 and 4.27 ^V, respectively). Interestingly, theLPP amplitude was not sensitive to the negativity bias in priorstudies in which the valence of the evaluative context was ma-nipulated within subjects (Cacioppo etal., 1993). Whetherandunder what conditions the LPP is subject to a negativity bias isa matter for future research.

General Discussion

The foundation for the scientific study of attitudes was estab-lished by Thurstone (1928) when he outlined a self-report tech-nique for assessing attitudes that was based on the theory andmethods of psychophysics. The application of ideas from psy-chophysics helped characterize attitudinal processes as involv-ing (a) an evaluative percept (categorization) of a stimulus and(b) a bivalent action disposition toward the stimulus (Berntson,Boysen, & Cacioppo, 1993). Self-reports and other efferent be-havioral responses are a function of both the evaluative perceptand the bivalent action disposition and thus are susceptible tointentional and unintentional nonattitudinal factors that selec-tively influence response selection and execution. Because theevaluative percepts that underlie attitudes can be obscured dur-ing the behavioral expression of attitudes, the reliance on self-report measures may have restricted the study of attitudinalprocesses.

Consistent with our previous research (i.e., Cacioppo et al.,1993, 1994), results of the present studies revealed that, whenparticipants evaluatively categorize stimuli, a larger amplitudeLPP is evoked by evaluatively inconsistent stimuli than by eval-uatively consistent stimuli. Importantly, the findings of thesetwo studies extend those of our earlier research by demonstrat-ing that the amplitude of the LPP to a stimulus and an individ-ual's attitude report to that stimulus can be functionally sepa-rated. Instructions to misreport the valence of stimuli led to theinstructed changes in attitude report, but these attitude-reportinstructions did not significantly change the amplitude of theLPP. Thus, these results provide support for the notion that theamplitude of the LPP is particularly sensitive to variations inevaluative categorization, rather than response, processes andsuggest that the LPP could be used to assess the evaluative cate-gorizations that underlie attitudes even if people intentionallymisrepresent their attitudes.

The procedure for examining evaluative categorizations usedin the present studies represents an application of principlesfrom research on the P300 component of the ERP, and theshared characteristics between the LPP observed in these stud-ies and the P300 suggest that the LPP and the P300 are similar.Research on the P300, for example, has revealed that stimulithat are categorically inconsistent along a task-relevant dimen-sion evoke a large P300 compared with stimuli that are categor-ically consistent along the task-relevant dimension. In the pres-ent studies, the evaluative dimension was made task-relevant to


participants, and the categorical significance of each stimuluswas manipulated by varying its evaluative significance (i.e.,valence). A principal difference between this research and re-search on the P300, therefore, is that participants in these stud-ies were required to categorize stimuli along an evaluative di-mension, rather than along a nonevaluative (e.g., physical,semantic) dimension, as is typical in research on the P300. Aswould be expected given these similarities, the LPP evoked inthese studies displayed the signature characteristics of the P300as (a) its average latency was between 300 and 900 ms followingthe onset of a stimulus and was similar to the latency of the P300evoked by semantic categorization tasks (e.g., Bentin et al.,1992; Ritter, Simson, & Vaughan, 1983), (b) its amplitude waslarger over the midline centroparietal than the frontal areas ofthe scalp; (c) it was larger to categorically (i.e., evaluatively)inconsistent stimuli than to categorically consistent stimuli, and(d) it was not affected by postcategorization response processes.Thus, these shared characteristics suggest that the LPP evokedin these studies is the P300 component of the ERP. Recent re-search, however, has revealed that evaluative, as compared withnonevaluative, categorizations evoke a late positive (P300-like)potential that is relatively larger over the right than the left scalpregions (Crites, 1994). Although the similarities between thepotentials evoked by evaluative and nonevaluative categoriza-tions are consistent with the notion that evaluative and noneval-uative categorization processes share at least an important sub-set of information processing operations and neural generators,the difference in the lateral scalp distribution of the potentialssuggests that evaluative and nonevaluative categorizations haveat least partially distinct information processing operations andneural generators. Thus, although many of the same informa-tion processing operations may underlie the LPP evoked byevaluative categorizations and the traditional P300 componentof the ERP (i.e., evoked by nonevaluative categorizations), weuse the generic term late positive potential or LPP to refer to thepotential evoked when participants evaluatively categorize stimuli,because evaluative and nonevaluative categorizations may involveslightly different information processing operations.

The findings from research on the P300 in conjunction withfindings from the present studies suggest that the LPP couldbe used to assess attitudes that people are unwilling to report.Research on the P300 has demonstrated that the amplitude ofthe P300 can be used to make inferences concerning the pres-ence or absence of "guilty" knowledge even when individualsdo not reveal this knowledge (Allen et al., 1992; Farwell & Don-chin, 1991; Rosenfeld et al., 1991). For instance, participantsin Farwell and Donchin's (1991) study gleaned relevant detailsabout a particular crime by participating in a mock crime. Par-ticipants subsequently were shown a series of stimuli in whichcrime-related stimuli were presented infrequently within acontext of stimuli that were not related to the crime. The crime-related stimuli evoked a larger amplitude P300 than unrelatedstimuli only in participants who had taken part in the mockcrime. Thus, as in the present research, Farwell and Donchinfound that a component of the ERP can differentiate stimulithat are categorically inconsistent with the contextual stimulifrom stimuli that are categorically consistent with thecontextual stimuli, even though the participants' verbal or overt

responses do not differentiate these two categories of stimuli.Given the similarities between the LPP evoked by evaluativecategorizations and the P300, these findings suggest that theLPP could be used to study attitude percepts without relianceon an attitude report and could potentially be used to assessattitudes that people are unwilling to report.

In addition, research on the P300 offers the interesting possi-bility of an objective assessment of information of which peopleare not consciously aware. Renault, Signoret, Debruille,Breton, and Bolgert (1989) showed pictures of familiar and un-familiar faces to an individual with prosopagnosia who was un-able to recognize familiar faces (e.g., self, spouse). The partici-pant was shown a set of familiar faces embedded in a larger setof unfamiliar faces, and the participant's task was to classify thepictures as either familiar or unfamiliar. Typical of prosopag-nosic individuals, the participant could not consciously differ-entiate between pictures of familiar and unfamiliar faces. TheP300 evoked by familiar faces, however, was larger than thatevoked by unfamiliar faces. Thus, as in the present research,the amplitude of an ERP component reflected differences incategorization processes even though the participant's verbalresponse to the stimuli did not differ. It remains for future re-search to determine whether the LPP paradigm can also be usedeffectively to assess attitudes that people are unable as well asunwilling to report.

Though an attitude measure based on the LPP of the ERPoffers the potential to assess attitudes that individuals may beunwilling or unable to report accurately, the requirementsin terms of time and resources for making a single attitudeassessment make an ERP attitude measure impractical inmany circumstances. For instance, the amplitude of the LPPvaries as a function of evaluative inconsistency only whenparticipants implicitly or explicitly categorize stimuli alongan evaluative dimension. Furthermore, individuals must bepresented with numerous presentations of a target stimulusto obtain a single ERP waveform to that stimulus, andmultiple ERP waveforms are needed to make a single attitudeassessment (i.e., because the LPP associated with a targetstimulus must be compared with the LPP associated withother known stimuli). The heavy investments in time, re-sources, and technical demands that are necessary for mak-ing a single attitude assessment, therefore, would most likelylimit an ERP measure of attitudes to circumstances in whichself-report measures absolutely cannot be used.

Given the limitations of using the LPP as a means of assessingattitudes, the promise of the LPP paradigm is its ability to ex-amine stages of the attitudinal process and obtain informationconcerning the attitudinal process that cannot be obtained oris difficult to obtain using only behavioral responses. Althoughinferences concerning information processing stages that un-derlie psychological (e.g., attitudinal) processes can be madeusing only behavioral responses (e.g., Donders, 1868/1969;Sternberg, 1969), the nature of these inferences are limited (seee.g., Van der Molen, Bashore, Halliday, & Callaway, 1991). Thepresent studies, as well as research on the P300, suggest thatthe LPP more directly assesses categorization, as opposed toresponse, processes. Behavioral responses, on the other hand,are a function of both attitudinal percepts and response pro-


cesses. Because these two measures assess different sets of infor-mation processing stages, they may, when used in concert withone another, provide a means of examining interactive effects offactors on attitudinal processing stages that cannot be examinedwhen only a single measure is used (see, e.g., Coles, Gratton,Bashore, Eriksen, & Donchin, 1985).

In addition to the amplitude of the LPP, there are other as-pects of the LPP and the ERP that may provide useful informa-tion concerning the information processes that underlie attitudejudgments. The temporal latency of ERP components, for ex-ample, reflects the relative latency of the information process-ing operations that give rise to the components (e.g., Coles et al.,1990; Donchin & Coles, 1988; McCarthy & Donchin, 1981).Although analyses on the latency of the LPP evoked in Studies1 and 2 revealed no significant systematic effects, the latency ofthe P300 is known to increase as a function of the complexityor difficulty of the categorization task (e.g., Fabiani et al., 1987;Kutas, McCarthy, & Donchin, 1977). The latency of the LPP,therefore, could potentially be used to examine the latency ofdifferent types of evaluative categorizations. In addition,differences in the shape or scalp distribution of the ERP, orcomponents of the ERP, might provide useful information con-cerning changes in information processing operations (e.g., seeJohnson, 1993).

Finally, the present research has parallels to the variable per-spective theory outlined by Ostrom and Upshaw (1968), inwhich they distinguished between the content of an attitude andthe judgmental language or rating used to describe the attitude.The content of an attitude refers to the various ideas, beliefs,images, and elements associated with the attitude stimulus andthe evaluative position summarizing this information. The rat-ing of an attitude refers to how the person presents this evalua-tive position on an evaluative dimension. Although variable per-spective theory focused on the mediating relationship of one'sperspective between the content and the rating of one's attitude,Ostrom and Upshaw's distinction between attitude percept andattitude rating predates the present analysis. As in their earlywork, the present studies also provide evidence that factors inthe social world can have differential effects on these two aspectsof attitudinal processes. In that sense, the present research re-flects both something old and something new.

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Received June 6,1994Revision received December 27,1994

Accepted January 5,1995 •