Personality effects on attentional shifts to emotional charged cues: ERP, behavioural and HR data

Personality and Individual Di€erences 29 (2000) 217±238

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Personality e€ects on attentional shifts to emotional charged cues: ERP, behavioural and HR data p Vilfredo De Pascalis*, Osvaldina Speranza Department of Psychology, University of Rome ``La Sapienza'', Rome, Italy Received 12 October 1998; received in revised form 18 June 1999; accepted 17 August 1999

Abstract Three orthogonal personality factors were derived from a joint analysis of EPQ and SSS-V questionnaires: (1) extraversion Ð sensation seeking (E-SS); (2) psychoticism Ð sensation seeking (PSS); (3) anxiety (Anx). P300 amplitude, heart rate (HR) and reaction times (RTs) and emotional ratings were obtained from 59 subjects during a spatially cued stimulus recognition task. Pleasant, unpleasant and neutral words served as cues in a covert attention spatial orienting task. Split plot ANOVAs were performed between high and low level groups selected on the basis of three orthogonal factors. High ESS subjects displayed more intense feeling for pleasant words than did low E-SS subjects. There were higher P300 peaks in high E-SS subjects compared to low E-SS ones for stimuli delivered in the left hemi®eld over frontal and parietal cortical regions. Low P-SS subjects, compared to high P-SS ones, had greater HR acceleration responses and greater P300 peaks across neutral- and pleasant-cued targets. The Anx dimension was independent from other personality factors and sensitive in detecting larger HR accelerations for unpleasant cueing in high Anx subjects as compared to the low ones. High Anx scores had slower RTs in detecting both pleasant and neutral cued targets. Results are discussed in terms of Eysenck's, Gray's and Zuckerman's models. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Personality; Visual event-related potential; Heart rate; Reaction time; Memory

Paper presented at the 9th World Congress of Psychophysiology (Symposium 18), 14±19 September 1998 Taormina, Sicily, Italy. * Corresponding author. Tel.: +39-6-4991-7649; fax: +39-6-445-1667. E-mail address: [email protected] (V. De Pascalis). p

0191-8869/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 1 9 1 - 8 8 6 9 ( 9 9 ) 0 0 1 8 9 - 0

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1. Introduction The event-related potential (ERP) is thought to re¯ect di€erent aspects of information processing and to provide a direct measure of stimulus processing and response organization. The P300 (P3) component of the ERP is assumed to re¯ect some attentional and cognitive processes more than other ERP components. The P300 amplitude enhances as the novelty (or unexpectedness) of the event and re¯ects the allocation of attentional resources to the stimulus. A number of studies have investigated the relationship between introversion/extraversion and P300 component for its relevance to the arousal mechanism in Eysenck's theory (see review of Eysenck, 1994; Geen, 1983; Zuckerman, 1991). In their recent review, Matthews and Gilliland (1999) pointed out that early studies of ERP measures were notable for their inconsistent results probably because the relations of cortical arousal, arousability and the arousal potential of experimental conditions with the ERP components were not clearly understood. An overlapping result among a number of recent studies is the ®nding that P300 is higher in introverts than extraverts. Stelmack and Houlihan (1995) interpreted this ®nding as suggesting that introverts are experiencing greater levels of attentional demand, a result which may implicate higher levels of arousal in introverts (Eysenck, 1994). Failures to replicate e€ects across similar studies have stimulated researchers in evidencing a number of possible experimental e€ects that moderate the relationship between P300 and extraversion (E). According to Di Traglia and Polich (1991) the increased P300 amplitude in introverts may be the result of smaller habituation in these subjects compared to extraverts and, therefore, it is more likely to occur in sessions with a large number of trials. Stenberg (1994) has suggested that P300 is larger in extraverts when the task is complex or requires more processing capacity. Brocke, Tasche and Beauducel (1997) showed that under di€erent levels of stimulation the negative relationship between E and P300 amplitude became positive when subjects during a visual vigilance task received an additional 60 dB white noise. This e€ect has been attributed to transmarginal inhibition which starts its operation at lower levels of stimulation in introverts (Eysenck, 1981). In the ®eld of personality, Je€rey Gray (1982; 1991) has developed an alternative theory of extraversion/introversion based on the activity of two systems that are responsible for emotional behavior: (1) the behavioral approach system (BAS), which mediates approach to signals of reward and relieving non-punishment; (2) the behavioral inhibition system (BIS) which is activated by conditioned stimuli of punishment and corresponds to the subjective state of anxiety. According to this theory, the BAS is more sensitive in extraverts and the BIS is more sensitive in introverts. Extraverted subjects should display a higher susceptibility to signals of reward (positive emotions) than to signals of punishment (negative emotions). The opposite should be observed for introverts. Anxiety is regarded as the emotion close to high levels of neuroticism (N) and low levels of psychoticism (P) and, therefore, most directly linked to the activity of the BIS. High N subjects should enhanced response to punishment signals (negative emotions) and not to reward signals (positive emotions). In terms of Eysenck's theory the BAS should be associated primarily with high E and secondarily with high N and P levels, which describe impulsivity as a personality dimension (Gray, 1987). Eysenck (Eysenck, 1967; 1981; Eysenck & Eysenck, 1985) conceptualized individual di€erences in N and E with respect to emotional processing in terms of direct output from

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a€ect or mood. Neuroticism results from a lower threshold for activation in the limbic system which is particularly responsible for negative emotions. High levels of N are associated with frequent experiences of negative emotions. E is the result of individual di€erences in the level of the ascending and descending reticular systems and other arousal systems. Eysenck (1967) claims that extraverts are less conditionable than introverts, but makes no distinction between these subjects for reward and punishment. Finally, Zuckerman (1991) and Zuckerman, Joireman, Kraft and Kuhlman (1999) have suggested that generalized expectancies of reward and punishment are more relevant to human behavior than speci®c sensitivities to conditioned stimuli. Reward expectancies are associated with positive a€ect and are characteristic of extraverts. Punishment expectancies are associated with negative a€ect and are characteristic of neurotic-anxious individuals. Extraverts engage in compensatory arousal seeking activities such as seeking novelty and excitement and being sociable. The hypothesized links of E with the level of positive a€ect, but not negative a€ect and N with the level of negative a€ect, but not positive a€ect, have been supported by a number of correlational studies (Costa & McCrae, 1980; Larsen & Ketelaar, 1989; 1991; Rusting & Larsen, 1997). The Psychoticism (P) factor has not been as widely studied as E, but its link to conditionability (Eysenck & Levey, 1972) suggests that it may be related to emotional arousal. High P scorers are described as being impulsive and antisocial individuals who are low in sensitivity to positive and high in sensitivity to negative emotional feeling (Costa & McCrae, 1980; Eysenck, 1997; Hepburn & Eysenck, 1989; Tellegen, 1985; Williams, 1990). High P subjects should be less sensitive to stimuli associated with positive emotions and more sensitive to stimuli associated with negative emotions. According to Zuckerman's (1993) model the aroused type of positive a€ect like ``elation'' is a characteristic of impulsive sensation seeking which is related to low expectancies of punishment and high expectancies of reward. The P dimension was found strongly related to sensation seeking (SS) dimensions (Eysenck & Zuckerman, 1978) and has been reconceptualized by Zuckerman (1989) as a combination of impulsivity, sensation seeking and lack of socialization. Therefore, in this study Zuckerman's SS dimensions and Eysenck's personality dimensions were analyzed in order to obtain orthogonal personality variables corresponding as closely as possible to the N, E and P dimensions. A small number of ERP studies have attempted to test Gray's and Eysenck's theories. Bartussek and colleagues have reported a number of studies devoted speci®cally to test Gray's theory. Bartussek, Naumann, Moeller, Vogelbacher and Diedrich (1990) recorded ERPs from introverts and extraverts to emotionally positive, negative and neutral adjectives. Positive and negative adjectives were used to di€erentiate reward seeking (BAS) and punishment avoidance (BIS) components. Results failed to support Gray's theory, introverts had greater ERP amplitudes to neutral adjectives and extraverts had greater ERP amplitudes in both positive and negative adjectives. Bartussek, Becker, Diedrich, Naumann and Maier (1996) reported two ERP experiments devoted to test the relationship between E and motivational stimuli, one requiring processing of adjectives of di€ering emotional valence, one using a startle response paradigm with foreground stimulation consisting of emotionally positive, negative and neutral slides. In the ®rst experiment complex interactions involving E, emotional valence, processing task and electrode locations were found for P300; similar e€ects were obtained in the second study for P200 peak amplitude. The authors suggested that extraverts tend to develop higher

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levels of arousal at frontal sites irrespective of emotional valence of the stimuli. These results failed to support Gray's theory and, assuming that emotional stimuli induce transmarginal inhibition in introverts, appear to support Eysenck's general arousal model. Another line of research has shown that high SS subjects tend to increase a P1-N1 peak amplitude of the ERP both with auditory and visual stimuli with increasing stimulus intensity (augmenting), while low SS subjects reach their maximum amplitude at lower intensities (reducing). In particular, the Disinhibition subscale of the sensation seeking scale (SSS) yielded the most robust results linking SS to augmenting of auditory and visual ERPs (Buchsbaum, Haier & Johnson, 1983; Zuckerman, 1990; Zuckerman, Buchsbaum & Murphy, 1980; Zuckerman, Simons & Como, 1988b). Considering that a mid stimulation may generate a positive hedonic tone and a high stimulation a negative hedonic tone, these results can be regarded as indicating that high SS subjects, with respect to the low ones, need a higher level of stimulation to experience a negative hedonic tone. In a study carried out in our laboratory (De Pascalis, 1994) high Dis subjects displayed greater posterior-occipital P2 peaks in the left hemisphere than low Dis ones. This result was viewed as supporting the hypothesis that high Dis subjects are augmenters and low Dis are reducers. Barratt, Pritchard, Faulk and Brandt (1987) found a positive relationship between impulsivity and augmenting of the visual ERPs. This relationship was also con®rmed in a recent odd-ball study wherein motor impulsiveness was found to relate positively with the amplitude of the P300 component of the ERP recorded at parietal leads (Harmon-Jones, Barratt & Wigg, 1997). Inter-beat-interval measure of phasic heart rate (HR) response to discrete stimuli is a good tool for assessing biological bases of personality and temperament (e.g. Barry, 1996; De Pascalis, Destro Fiore & Sparita, 1996; De Pascalis, Strelau & Zawadzki, 1999; Kaiser, Beauvale & Bener, 1997). Phasic heart rate response was observed by Lacey and Lacey (1970; 1974) using a ®xed foreperiod reaction time (RT) paradigm. These authors observed a phasic HR deceleration starting prior to an anticipated event which required the `intake' of sensory information conveyed by the signal. By contrast, situations requiring subjects to reject sensory input or simply to be involved in a cognitive task related to the stimulus signi®cance produced cardiac accelerations. According to Jennings (1992), neurophysiological bases of this deceleration should involve the same inhibitory neural circuitry that has been suggested by Gray (1982). In contrast, the occurrence of a HR acceleration response, indicates that processing capacity is allocated to ongoing mental and motor activities. A smaller HR acceleration, like that observed during a motor response, re¯ects the operation of an inhibitory process in the output system. Orlebeke and Feij (1979) delivered a series of ten 80 dB tones to high and low subjects on the disinhibition (Dis) subscale of the SSS. The high Dis subjects showed more immediate and stronger HR decelerations to the stimulus than those scoring low on Dis. The low Dis subjects showed more immediate and stronger accelerations than did high Dis subjects. These results were con®rmed by Ridgeway and Hare (1981) and Zuckerman et al. (1988b) using stimuli ranging from 55 to 90 dB. These studies evidenced that the larger HR acceleration found in low SS as compared to high SS subjects was even more pronounced with high intensity of stimulation which tends to produce negative emotion. Recently, in a study aimed to verify Gray's theory (De Pascalis et al., 1996), a more pronounced HR deceleration was found for punishment compared to reward signals in introverts, while the opposite was found in

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extraverts. Kaiser et al. (1997) reported enhanced HR deceleration responses to relevant auditory stimuli in high N subjects as compared to low ones. They also found smaller HR decelerations to irrelevant tones and smaller HR accelerations to relevant tones in high P subjects, as compared to low P subjects. Starting from the above mentioned experimental evidences, the aim of the present study was to evaluate the relationship between personality and P300 peak amplitude in two steps. First, it examines the relationship between E, N, P, L and Zuckerman's Sensation Seeking (SS) dimensions. Second, it explores the e€ects of emotional activation on P300 peak amplitude considering the relationship between Eysenck's and Zuckerman's dimensions. The measurement conditions used are positive, negative emotional words and neutral words used as a control condition. The words are used as visual cues indicating the occurrence of a neutral target stimulus according to a cue-target paradigm developed by Posner, Cohen and Rafal (1982). This type of task has successfully evidenced that emotionally charged cues a€ect attentional shift to a neutral target detection by producing enhanced P1 and P300 peaks when emotional words served as cues (Stormark, Norbdy & Hugdahl, 1995). In the present study, the e€ects of positive and negative stimuli are regarded respectively as rewards and punishments and the degree of brain activation on P300 peak and HR changes following the presentation of such stimuli are examined both in the light of Gray's and Eysenck's hypotheses. More in particular, according to Gray's predictions we expected to ®nd higher emotional sensitivity, enhanced P300 peaks and HR changes for positive emotion in extraverts and for negative emotion in introverts. High N subjects, as compared to the low ones, should display higher emotional sensitivity, enhanced P300 peak and more pronounced HR changes for negative emotions and no di€erences for positive emotions. On the other hand, according to Eysenck's and Zuckerman's predictions extraverts should display higher emotional sensitivity, greater P300 peaks and HR changes for positive, but not for negative emotions. High N subjects should also display more pronounced behavioural and physiological responses for negative emotions. High P scorers, as compared to the low scorers, should display greater P300 peaks and HR changes for negative emotional stimuli and smaller P300 and HR responses for positive stimuli. Finally, according to Zuckerman's model, extraverted sensation seekers should display a higher sensitivity to positive emotions being more sensitive to reward. Therefore, we expected to ®nd more pronounced behavioural and physiological reactivity to positive emotion in subjects characterized by high levels of extraversion and sensation seeking. 2. Method 2.1. Subjects Subjects were 62 (41 women and 21 men) students aged 19±26 yr (women: 22.921.58; men: =23.4 2 4.13), all right handed. Handedness was evaluated using the Italian version of the Edinburgh Inventory Questionnaire (Salmaso & Longoni, 1985). Testing was carried out between 9 and 12 a.m. All subjects were screened for normal vision. Subjects who had reported psychiatric or neurological disorders were excluded from participation. Only women out of

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menstrual period were invited for physiological recordings. Three subjects (two women and one man) were rejected because of artifacts on HR and EEG activities during the tasks. Participants were not informed about experimental hypotheses. 2.2. Personality measures Personality tests administered were the Italian version of the Eysenck Personality Questionnaire (EPQ-R: Eysenck, Eysenck & Barrett, 1985; San Martini, Mazzotti & Setaro, 1996) and the Sensation Seeking Scale Ð Form V (SSS-V) (Zuckerman, 1979; Italian translation of the SSS-V). 2.3. Task, stimuli and procedure Presentation of visual displays, timing and recording of manual RT data were obtained using a speci®c software developed for this study that was running on an IBM PC. The task consisted of Posner's (1988) covert spatial attention task modi®ed by Stormark et al. (1995) in order to investigate how emotionally charged information in¯uences cued attentional shifts. Spatial locations were designed by two rectangles, one to the left and one to the right of a centre ®xation point. At the start of each trial the subject ®xated a plus sign (+) placed at the center of the computer screen. In one of the two rectangles suddenly appeared an emotionally charged word which served as a cue and draws the subject's attention to that location. An asterisk (), which is the neutral target, then appeared on the screen either in the rectangle which was lit up (validly cued target) or in the rectangle in the opposite visual ®eld (invalidly cued target). The subjects were instructed to respond as quickly as possible by pressing a hand button with their right thumb whenever the target appeared on the screen. The attention task consisted of three di€erent conditions with a total of 720 trials. In the `valid' cue condition the target stimulus appeared in the same hemi®eld as the cue. This occurred on 2/3 of all trials. In the `invalid' cue condition the target appeared in the hemi®eld opposite where the cue was presented. This occurred on 1/6 of all trials. A third condition was the no-cue condition where the target occurred without the cue (1/6 of the trials). The no-cue condition was included only to prevent subjects from developing an automatised response set due to the ®xed cue-target interval. Therefore, this condition was scored separately and not included for data analyses. Half of the cues and the targets were presented in the right and half of them in the left hemi®elds. The subject was required to ®xate a centrally placed + sign on the computer screen and to respond as fast as possible by pressing a button with the right thumb for RT recordings whenever the target asterisk appeared on the screen. Cues and targets were presented inside a rectangle on the computer screen (100 cm distance of observation) that was 2 cm high  4.3 cm wide, in either the left or right hemi®elds with 3.78 of visual angle from the ®xation point. The screen was mounted on one side of a tunnel-guide, while the other side served to the subject to ®xate the screen. Visual display was in an electrically shielded cubicle. The cubicle was dimly lit with the visual stimuli easily visible in the tunnel display (200 Cd/m2). All recording equipments were located outside the box. The inter-stimulus interval between the onset of the cue and the target was 1100 ms. The cue was displayed for 300 ms and the target for 100 ms. The inter-trial interval was 800 ms. Before

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the experiment started, each subject received 15 practice trials. Ten emotionally salient Italian words with negative valence (unpleasant words, e.g. cretina/o, idiota, cattiva/o, scema/o, brutta/o), ten with positive valence (pleasant words, e.g. bella/o, brava/o, lieta/o, carina/o, felice) and ten neutral words (e.g. pianta, vetro, sedia, borsa, foglio) served as cue stimuli. The words were selected from a pool of 100 Italian words that were rated for their emotional evocativeness by an independent sample of 30 subjects considering their emotional valence and frequency of usage. Each word length was between 5 to 6 letters with the exception of one unpleasant word that consisted of 7 letters. The stimuli were administered in three separate sections of 240 trials each. The sections were separated by a relaxation time interval of 5 min. Each section consisted of stimuli presented in 5 blocks of 48 trials each. In each block there were trials, according to a ®xed random schedule, appertaining to each of three di€erent experimental conditions (valid-cue, invalid-cue, no-cue). Subjects were invited to sit, in a sound-attenuating cubicle, on a comfortable chair and were informed about the experimental procedure. They were checked for normal vision and asked to complete the handedness questionnaire. The cap for the EEG and electrodes for EOG and cardiac recordings were attached. At the end of the experimental tasks, a word-recognition test was ®rst administered in which the subjects were asked to indicate which words out of a list of 60 had served as the cue stimuli. Among the words in the list were the 10 pleasant, 10 unpleasant and 10 neutral words that had served as cues in the attentional task. The new 30 words in the list appertained equally to the pleasant, unpleasant and neutral emotional categories. After the memory test the subjects were required to rate on a 10-point scale (i.e. from 0=no emotion at all to 10=very high emotion) the degree to which they experienced positive, negative and neutral emotions after the presentation of the emotional cues. 2.4. ERP and HR recordings ERP recordings were made using a cap (Electro-cap International) with pure tin electrodes from F3, F4, T5, T6, P3, P4, O1 and O2 scalp sites according to the international 10-20system. Linked earlobes served as the reference and subjects were grounded on the forehead. Electrode impedance was maintained under 5 KO and EEG was recorded using a time constant of 3 s and a 75 Hz low pass ®lter. The EOG was recorded with two electrodes placed above and below the left eye. The EEG was recorded by neuroencephalograph (`ERA9'; OTE Biomedica Italiana) and digitized on-line (by an analog to digital converter connected to an IBM PC/AT) with a sampling rate of 341.3 Hz and stored on a hard disk for later processing. Separate visual ERPs were recorded for the cue word and target stimulus. An epoch of 1208 ms was used for averaging with 252 ms baseline preceding the stimulus onset. After the experiment, ERPs were averaged o€-line for target stimuli. In order to control for ocular or motoric artifacts, all epochs with EOG amplitudes above or below 50 mV were excluded from further analysis. The number of averaged ERP responses was maintained between 40 and 45 for each stimulus. The interbeat intervals (i.e. the time between two R waves of the electrocardiogram) were recorded by a SATEM-Biolab PT104 SC with a PT411S Satem interface. R±R intervals (ms) were obtained from an electrocardiogram recorded with two silver±silver chloride electrodes, one attached to the manubrium sterni and the other to the left rib cage. R±R intervals were

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o€-line expressed in beats per minute (bpm). For each trial a recording epoch of 3 s was used. The sampling frequency was of 5 Hz. Measures of cardiac activity were calculated in terms of mean values of HR at 0.2 s intervals for 3 s epochs commencing 1.6 s before each target stimulus and 0.6 s before each cue word. For each epoch HR changes were obtained by subtracting each HR value from the HR at 1.6 s from target stimulus onset (time 0). Each section of 240 trials lasted about 12 min and, therefore, an overall recording period lasted 36 min.

2.5. Data reduction Each single trial ERP was separately averaged across target stimuli linked to pleasant, unpleasant and neutral words (40 R n R 45 recording epochs) by producing electrocortical and cardiac event-related responses to neutral targets for the di€erent types of words. ERP peak measure was the baseline to peak amplitude of a positive peak P300 in the 300± 500 ms latency range (P3: latency=423.2 2 63.9 ms). P300 peak was de®ned as the positive local maximum of the ERP between 300 and 500 ms after stimulus onset and baseline. This measure was obtained after visual inspection of the ERP by using a speci®c software with ASYST-Keythley programming system. In order to obtain a normal distribution of P300 peak amplitudes, a log transformation of P300 data plus one was used as database for statistical analyses. Measures of cardiac activity were calculated in terms of mean values of HR at 0.2 s intervals for 3 s epochs commencing 1.6 s from target stimulus onset. An HR acceleration response was observed preceding the cue word and the target stimulus onset that reached a maximum with the emission of the motor response. The HR acceleration continued after the onset of the word (1.1 s preceding the target stimulus) and was modulated by the mental activity involved in the processing of the cue word.

2.6. Data analysis Separate repeated measures ANOVAs across behavioural and physiological data, were computed for each personality factor used in this study. The experimental design used for P300 peak was: 2 Personality (high, low)  2 Hemi®eld (left, right)  2 Cue-Validity (valid, invalid)  2 Hemisphere  4 Electrode Location (frontal, temporal, parietal, occipital)  3 Emotion. Because of the risk of falsely signi®cant results in repeated measures ANOVAs if the sphericity assumption has been violated (Vasey & Thayer, 1987), MANOVAs were used to test for overall signi®cance of e€ects. Huynh-Feldt corrections of degrees of freedom were applied when necessary. Post hoc comparisons of the means were carried out by Duncan's Multiple Range Test ( p < 0.05). The signi®cant e€ects that are considered essential for the questions addressed in this study are reported.

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3. Results 3.1. Personality Pearson's intercorrelations between EPQ-R dimensions and SSS-V subscales are given in Table 1. The intercorrelations between the scales of the two questionnaires are in agreement with the predictions from Zuckerman's theory (Zuckerman, 1994) and with previous ®ndings (Eysenck & Zuckerman, 1978). The P dimension showed a positive signi®cant …p ˆ 0:0213† correlation with TAS and highly signi®cant correlations with ES, Dis and BS. With the exception of BS, the E dimension also displayed signi®cant relationships with SSS subtraits (Table 1). The highly signi®cant correlations among Eysenck's and Zuckerman's dimensions raises methodological problems in performing separate analyses for each personality dimension. The need to reduce the number of tests for personality e€ects in order to hold the Error I rate within limits, suggested a data reduction of the personality scales by factor analysis. Therefore the Eysenck's and Zuckerman's personality dimensions were jointly subjected to a Principal Component Analysis. A three factor solution was picked out and Varimax rotated. This choice was guided by the need to ®nd three orthogonal factors corresponding as closely as possible to Eysenck's concept of E, N and P. The 3 personality factors emerging from the factor analysis are presented in Table 2. This analysis was used as a purely heuristic tool to reduce personality data and obtain orthogonal measures of extraversion, psychoticism and neuroticism as a combination of sensation seeking dimensions. The ®rst factor embodies important aspects of extraversion and sensation seeking dimensions (E-SS), with high positive loading on E, TAS, ES, DIS and a moderate loading on BS. The second factor is a psychoticism and sensation seeking factor (P-SS) with high positive loadings on P and BS and a negative loading on L (social desiderability). The third factor is an anxiety factor (Anx) with the highest positive loading on the N factor and a negative loading on the L dimension. These three factors will be considered in further analyses, the ®rst and third factors being the most clearly related to the theoretical position of Gray (i.e. impulsivity and anxiety). A median split was performed on their distributions of factor scores in order to form high and low scoring groups for analyses of variance.

Table 1 Correlation matrix for EPQ-R and SSS-V measures: Extraversion (E), Neuroticism (N), Psychoticism (P), Lie (L), Thrill and Adventure-seeking (Tas), Experience-seeking (Es), Disinhibition (Dis), Boredom Susceptibility (Bs).  p < 0.05; p < 0.01; +p < 0.001; N = 59

E N P L

N

P

L

Tas

Es

Dis

Bs

ÿ0.103

0.164 0.004

0.186 ÿ0.37 ÿ0.239

0.441+ 0.111 0.299 ÿ0.213

0.582+ ÿ0.12 0.488+ ÿ0.028

0.400+ 0.175 0.417+ 0.020

0.248 0.163 0.395 ÿ0.517+

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3.2. Total sample analyses 3.2.1. Emotional feeling and word recognition test For emotional feeling ratings there was a main e€ect for Emotion (F2,56=40.52, p < 0.0001). This e€ect indicated that the emotional feeling for pleasant and unpleasant cues was greater than that for neutral cues (6.21, 6.49 and 3.92, respectively). An ANOVA for word recognition scores evidenced a main e€ect for the emotional type of words (F2,56=4.038, p ˆ 0:023). This e€ect revealed that signi®cantly more unpleasant words were correctly identi®ed than pleasant ones, while there were no di€erences in recognition scores between pleasant words compared to neutral words (9.2, 8.7 and 8.9 for unpleasant, pleasant and neutral words, respectively). 3.2.2. Reaction time The ANOVA for RT scores evidenced a main e€ect for Validity …F1,57 ˆ 8:13, p ˆ 0:0060† showing that there were shorter RTs for validly cued targets compared to invalidly cued ones (390.8 vs. 407.2 ms, respectively). The Validity  Hemi®eld …F1,57 ˆ 11:09, p ˆ 0:0015† and Validity  Emotion …F2,56 ˆ 4:69, p ˆ 0:011† interactions were also signi®cant. The ®rst interaction indicated that for validly cued targets pleasant and unpleasant cued targets produced longer RT than did neutral cued ones, while for invalidly cued trials there were no di€erences among emotion conditions (valid trials: 390, 392, 379 ms; invalid trials: 407, 403, 409 ms, respectively for pleasant, unpleasant and neutral cued targets). 3.2.3. P300 peak The ANOVA for P300 peak amplitude evidenced the following e€ects: (1) Location …F3,55 ˆ 108:8, p < 0.0001); (2) Emotion  Location …F3,55 ˆ 5:52, p < 0.01); (3) Hemi®eld  Hemisphere …F1,57 ˆ 11:6, p < 0.001); (4)Validity …F1,57 ˆ 22:0, p < 0.0001); (5)Validity  Location …F3,55 ˆ 17:6, p < 0.0001). The ®rst e€ect indicated that there were decreasing P300 peak amplitudes from frontal, parietal and temporal sites, while P300 peak over temporal sites Table 2 Factor loading of personality variables on factors derived from principal component analysis (N = 59) Factor 1 ES E TAS DIS BS P L N Variance explained (%)

2

3

0.82 0.81 0.80 0.79 0.42 0.27 0.20 0.05

0.33 ÿ0.08 0.26 0.22 0.80 0.79 ÿ0.67 ÿ0.01

ÿ0.07 ÿ0.16 0.06 0.16 0.13 ÿ0.15 ÿ0.54 0.94

44.16

20.52

11.87

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was quite similar to that found over occipital sites (1.29, 0.84, 0.64, 0.59 log(mV) for frontal, parietal, temporal and occipital sites, respectively). The second e€ect indicated that over frontal sites there were greater P300 peaks to targets for pleasant and unpleasant cued targets as compared to targets for neutral cued ones. The third e€ect displayed that, for targets delivered in the left hemi®eld, P300 peak in the right-hemisphere was greater than that in the left hemisphere (0.94 vs. 0.90, for right vs. left hemisphere, respectively). The opposite hemispheric trend was found for targets delivered in the right hemi®eld (0.92 vs. 0.97; for right vs. left hemisphere, respectively). The fourth e€ect indicated that P300 peak amplitude for valid cued targets was greater than that for invalid ones (1.83 vs. 1.38). Post-hoc comparisons using Duncan's test ( p < 0.01) evidenced for the ®fth e€ect that P300 peak over frontal sites was greater for valid as compared to invalid cued targets (2.58 vs. 2.34); an opposite trend was observed between valid and invalid cued targets for temporal (0.52 vs. 1.16) and parietal sites (1.12 vs. 1.46), while the di€erence for occipital sites was not signi®cant (0.85 vs. 1.01). 3.2.4. HR change Visual inspection of HR change scores displayed a clear HR acceleration response starting before the target stimulus onset and increasing with the emission of the RT motor response. The ANOVA on HR change scores evidenced the following e€ects: (1) Hemi®eld …F1,57 ˆ 8:04, p ˆ 0:006); (2) Time …F11,47 ˆ 10:72, p < 0.0001); (3) Hemi®eld  Time …F9,49 ˆ 2:74, p ˆ 0:0006); (4) Emotion  Time …F23,35 ˆ 2:11, p ˆ 0:023); (5) Validity  Emotion  Time …F28,1596 ˆ 2:18, p ˆ 0:00046). The ®rst three e€ects indicated that when the target was presented in the left hemi®eld it produced greater HR accelerations (0.5 bpm) compared to the right hemi®eld. The fourth e€ect indicated that pleasant and unpleasant cued targets produced greater HR accelerations than did neutral cued ones (1.80, 1.79 and 1.06 bpm, for pleasant, unpleasant and neutral cued targets, respectively).

3.3. Individual di€erences in personality: behavioural and physiological responses 3.3.1. Emotional feeling and word recognition test The ANOVA computed on emotional ratings split with respect to E-SS scores revealed a main e€ect for E-SS …F1:57 ˆ 6:24, p ˆ 0:015† indicating higher emotion ratings in high E-SS subjects compared to low E-SS ones. Moreover, the E-SS  Emotion was also signi®cant (MANOVA F2:56 ˆ 4:86, p ˆ 0:013). Duncan's test ( p < 0.01) indicated that there were no di€erences in emotional feeling between high E-SS and low E-SS subjects for unpleasant (5.2 vs. 4.9) and neutral cued targets, but for pleasant cued targets high E-SS subjects had higher emotion feeling than did low E-SS ones (5.4 vs. 4.0). Emotional rating scores also evidenced a signi®cant interaction of P-SS  Emotion (MANOVA F2:56 ˆ 7:91, p < 0.01), indicating higher emotional feelings in low P-SS subjects, as compared to high P-SS ones, for pleasant cued targets (5.3 vs. 4.1), while no group di€erences were obtained (Duncan's test, p < 0.05) for unpleasant (4.9 vs. 5.3) and neutral cued targets (3.9 vs. 3.9). No signi®cant e€ects involving Anx factor were found for emotional rating scores. The ANOVA performed on word recognition scores did not evidence signi®cant e€ects of personality.

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3.3.2. Reaction time The split-plot repeated measures ANOVA performed on averaged RT scores in high and low E-SS groups, yielded a signi®cant e€ect of E-SS  Validity (MANOVA F1:57 ˆ 11:27, p ˆ 0:0014). This e€ect indicated that, for validly cued targets, the low E-SS group had signi®cantly shorter RTs than the high E-SS group (402 vs. 426 ms); while for invalidly cued targets averaged RT did not di€er between groups (423 vs. 424 ms, for low and high E-SS group, respectively). The RT scores obtained for the high P-SS group were shorter than those for the low P-SS group (399 vs. 437 ms) (MANOVA F1:57 ˆ 4:80, p ˆ 0:0325). Finally, Anx scores yielded a signi®cant e€ect of Anx  Emotion (MANOVA F2:56 ˆ 3:68, p < 0.05). The high Anx subjects had longer RTs compared to low Anx ones for pleasant and unpleasant cued targets (Pleasant cues: 435 vs. 401 ms; Unpleasant cues: 430 vs. 405 ms; for high Anx and low Anx groups, respectively), while there were no di€erences in RTs between groups for neutral cued targets (410 vs. 402 ms; for high Anx and low Anx, respectively).

3.3.3. P300 peak P300 peak amplitudes evidenced a signi®cant main e€ect for E-SS …F1:57 ˆ 5:73, p ˆ 0:020). Inspection of the group averages showed the highest P300 peak to be in the extraverted sensation seekers group. Furthermore, the interaction E-SS  Hemi®eld was also signi®cant (MANOVA F1:57 ˆ 12:78, p < 0.001). This e€ect revealed that when the target stimulus was in the left hemi®eld high E-SS subjects, as compared to the low ones, evidenced the most pronounced increases in P300 peaks. Finally, P300 peak amplitude exhibited a signi®cant e€ect of E-SS  Hemi®eld  Location (MANOVA F3:55 ˆ 4:87, p ˆ 0:0028). This last e€ect indicated that high E-SS subjects, as compared to the low ones, had signi®cantly greater P300 peak over both frontal and parietal areas when the target stimulus was presented in the left hemi®eld ( p < 0.01; Duncan's test) (Fig. 1). No other e€ects involving E-SS factor were signi®cant in this analysis. The P-SS factor evidenced the following e€ects: (1) for P-SS  Validity  Emotion (MANOVA F2,56 ˆ 3:40, p ˆ 0:0368). This e€ect indicated that the low P-SS group, as compared to the high P-SS one, had greater P300 peaks across neutral- and pleasant-cued targets for valid trials. For invalid trials there were no di€erences between groups across emotional conditions. This e€ect is shown in Fig. 2. Moreover, the e€ects of P-SS  Hemi®eld  Hemisphere …F1,57 ˆ 7:87, p ˆ 0:0069† and of P-SS  Hemi®eld  Hemisphere  Location …F3:55 ˆ 3:88, p ˆ 0:0114† were both signi®cant. These e€ects indicated that the high P-SS group over temporal and parietal recording sites tended to display higher P300 peaks in the left hemisphere for stimuli delivered both in the left and in the right hemi®elds. The low P-SS group over temporal and parietal cortical regions displayed higher P300 peaks in the right hemisphere for stimuli delivered in the left hemi®eld and, viceversa, they showed an opposite hemispheric asymmetry for stimuli delivered in the right hemi®eld (Duncan's test p < 0.05). Group averages across electrode locations for stimuli delivered in the left and right hemi®eld are shown in Fig. 3. No signi®cant e€ects involving the Neuroticism dimension were found on P300 peak scores.

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3.4. Heart rate To test the hypothesis of di€erent emotional reactivity for di€erent personality groups, HR change scores were submitted to separate repeated measures ANOVAs. No signi®cant e€ects involving the E-SS factor were found. However, the P-SS factor scores demonstrated a signi®cant main e€ect …F1:57 ˆ 6:05, p ˆ 0:017† and a signi®cant interaction with Time (MANOVA F11:47 ˆ 4:14, p ˆ 0:013). This e€ect indicated that low P-SS subjects had greater HR accelerations as compared to high-SS subjects. Furthermore, the interaction P-SS  Emotion  Time was also signi®cant …F28:30 ˆ 2:58, MSe=0.98, p ˆ 0:006). Inspection of HR change scores over time indicated that low P-SS subjects, after the delivery of target stimuli,

Fig. 1. ERP grand means in high and low E-SS subjects for target stimuli delivered in the right and left hemi®elds. ERPs averaged across frontal (Fr), posterior temporal (Te), parietal (Pa) and occipital (Occ) electrode locations.

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had more pronounced HR accelerations for negative and positive cued targets than did high PSS subjects (see Fig. 4). The Anx factor yielded a signi®cant Anx  Time interaction …F11,47 ˆ 4:48, MSe ˆ 7:16, p < 0.0001) indicating that high Anx subjects produced greater HR accelerations than did low Anx subjects. The e€ect of Anx  Time  Emotion was also signi®cant …F28:30 ˆ 2:78, MSe ˆ 1:02, p ˆ 0:0035). This e€ect indicated that the high Anx, as compared to the low Anx group, had stronger HR increases in negative cued targets, while during positive and neutral conditions there were no signi®cant HR changes between groups. This interaction e€ect is shown in Fig. 5.

Fig. 2. Left and right hemispheres ERP grand means in high P-SS and low P-SS subjects, averaged over valid and invalid trials for unpleasant, pleasant and neutral cued targets.

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Fig. 3. P300 peak amplitude and standard errors (mV) on high and low P-SS subjects over left and right frontal (F3, F4), posterior temporal (T5, T6), parietal (P3, P4) and occipital (O1, O2) sites for target stimuli delivered in the left and right hemi®elds.

4. Discussion 4.1. Behavioural and physiological indices of emotional activation The present ®ndings indicate that emotional stimuli modulate attentional processes which in¯uence behavioral performance, localized brain electrical response and phasic cardiac activity. Subjects showed faster RTs to validly cued targets as compared to invalidly cued ones. Over frontal sites there were greater P300 peaks to targets for pleasant and unpleasant cued targets as compared to neutral ones. This ®nding is in agreement with those obtained in a

Fig. 4. Grand means of evoked cardiac response obtained in high P-SS and low P-SS subjects.

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number of previous studies (e.g. Johnston, Miller & Burleson, 1986; Johnston & Wang, 1991) and further support the hypothesis of a deeper processing of emotional as compared to neutral stimulation (e.g. Birbaumer & Elbert, 1988; Palomba, Angrilli & Mini, 1997; Rockstroh, Elbert, Canavan, Lutzenberger & Birbaumer, 1989; Schupp, Lutzenberger, Rau & Birbaumer, 1994). The larger P300 to emotional stimuli has been suggested to yield a relative cortical inhibition which might prevent additional information intaking. In parallel with P300 peak in this study both pleasant and unpleasant cued targets produced greater HR accelerations than

Fig. 5. Grand means of evoked cardiac response to pleasant (PLEAS), unpleasant (UNPLEAS) and neutral (NEUTRAL) cued targets in subjects with high and low Anxiety (H-Anx, L-Anx).

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did neutral cued ones. Assuming that HR acceleration indicates cortical inhibition to external stimuli (Lacey's rejection condition), the HR changes observed in this study for emotionally cued targets are congruent with the direction of P300 peak changes. Such an e€ect indicates that emotional stimuli were preferentially processed in comparison with neutral ones. Unpleasant words were remembered more than pleasant and neutral ones, a result which is in line with previous ®ndings reported by Stormarck et al. (1995). This ®nding, however, di€ered from that reported in other studies wherein both pleasant and unpleasant emotional slides were remembered more than neutral ones (e.g. Bradley, Greenwald, Petry & Lang, 1992; Palomba et al., 1997). 4.2. Personality and emotional activation In the present study principal component analysis yielded correlational patterns which are in agreement with the correlational literature (Eysenck & Zuckerman, 1978; Zuckerman, 1974; Zuckerman et al., 1993) and evidenced that sensation seeking is a trait which falls between the E and P dimensions. In particular, the following relationships were found: (1) all subscales of SSS-V, with the exception of the BS subscale, were all positively loading on a general Extraversion factor (E-SS) which de®nes sensation seeking as an uninhibited, impulsive, dominant type of extraversion; (2) both BS and L (Social desirability) dimensions embody important aspects of Eysenck's Psychoticism dimension (P-SS); (3) the N dimension was positively and L negatively related to a general anxiety factor which was independent from the SS dimension. Given the ®ndings that emotional activation could produce measurable changes in ERP responses and HR activity, results from the present study are in agreement with the hypothesis that personality traits may interact with the strength and the direction of such changes. However, high and low levels of the Extraversion-Sensation seeking (E-SS) factor did not evidence signi®cant interactions with emotion, RT, recognition memory and physiological measures. In contrast, emotional feeling rating of pleasant words was higher in high E-SS subjects as compared to low E-SS ones. This result supports the hypothesis that extraverts are more sensitive to positive emotions than introverts, but the lacking relationship between E-SS and emotion for memory, RT and physiological measures do not seem compatible with Gray's and Zuckerman's models. However, a more general main e€ect of E-SS and an interaction of this factor with the hemi®eld of stimulation and recording site were evidenced for the P300 peak amplitude. These e€ects displayed higher P300 peaks in extraverted sensation seekers as compared to introverted sensation avoiders with more pronounced di€erences for stimuli delivered in the left hemi®eld over frontal and parietal regions in the right hemisphere. These results could be viewed as supporting Eysenck's more general arousal model if we assume that emotional cued stimuli induce a protective transmarginal inhibition, which may lead to paradoxically reduced arousal, in introverted sensation avoider. The ®nding of higher P300 amplitude in extraverts contrasts with the modal ®nding of larger P300 amplitude in introverts, a result which may indicate higher arousal in introverts (see, e.g. the review of Stelmack & Houlihan, 1995). But failures to replicate e€ects even across similar studies is a cause for debate (Zuckerman, 1991). It has been suggested that the increased P300 amplitude in introverts may be the result of greater habituation in extraverts (Di Traglia & Polich, 1991)

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and thus more likely to occur in sessions with a large number of trials. The validity of this suggestion was demonstrated by Cahill and Polich (1992) who manipulated the target stimulus probability, while setting time-on-task to a minimum to avoid habituation e€ects. Under these conditions, Extraverted subjects produced larger P300 peaks than introverts. These subjects also displayed a signi®cant stimulus probability e€ect by producing a steeper increase of peak amplitude with diminishing target stimulus probability. Stenberg's (1994) review of these ®ndings indicates that P300 is larger in extraverts when the task is of brief duration or the task is not monotonous and cognitively demanding. In line with these ®ndings are those previously reported by Orlebeke, Kok and Zeillemaker (1989) on the augmenting e€ects of P2 peak amplitude of the ERPs in high Dis subjects. The augmenting e€ect of ERP peaks in high Dis subjects was also observed in a number of studies (Zuckerman, 1994 for a review) and in a study carried out in our lab (De Pascalis, 1994). Therefore, the larger P300 peak in extraverted sensation seeker individuals should not appear a surprising result considering that (a) emotional stimuli and the cognitive demanding tasks used in the present study could have induced transmarginal inhibition in introverts and that (b) high sensation seekers are augmenting of the ERPs. On the other hand, if we assume that slow cortical positivities are a re¯ection of temporary reduced excitability (Birbaumer, Elbert, Canavan & Rockstroh, 1990), the larger P300 obtained in high E-SS subjects and the parallel slower RTs found for these subjects appear consistent with the view that P300 manifests a brief and widely distributed inhibitory event (Woodward, Brown, Marsh & Dawson, 1991). Finally, results of this study support the view that P is positively related to BS and negatively to social desirability as measured by the L scale. This ®nding is consistent with Zuckerman's (1989) reconceptualization of the P dimension as a combination of impulsivity, sensation-seeking and lack of socialization. Furthermore, the present results support the view that high P subjects when combined with high BS and low L ones (high P-SS subjects) tended to show electrocortical and autonomic signs of higher inhibition than low P combined with low SS and high L individuals (low P-SS). The main ®ndings in this respect were larger P300 amplitudes in the pleasant and neutral trials and larger HR accelerations in all measurement conditions for low P-SS subjects compared to the high ones. Low P-SS scorers also showed higher levels of emotional feeling rating for pleasant cued targets. The present ®ndings appear to support the hypothesis that low P-SS subjects are more sensitive to stimuli associated with positive emotions and con®rm Kardum's (1999) ®ndings in which psychoticism was signi®cantly negatively linked with positive a€ect intensity. It is known that the increased amplitude of the P300 component re¯ects an increase in attentional resource available for information processing, because these resources are allocated e€ectively (Ho€man, 1990; Wickens, 1984) or because of increased physiological arousal (Polich & Kok, 1995). Therefore, the larger P300 peak found in low-P SS subjects for pleasant stimuli may be seen as indicating an increased cortical arousal for this type of stimululation. Furthermore, the larger HR acceleration found for low P-SS subjects is in agreement with predictions, derived from Eysenck's (1992) theory, concerning the activation of lower brain stuctures. According to Eysenck, low P (or low impulsivity) levels are linked to high cortical arousal and this low cortical arousal relates to higher functioning of the brain stem reticular activating system. As cortical arousal decreases, the activity of lower brain structures is increased and the probability for the emission of impulsive behaviors is enhanced. In contrast,

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as cortical arousal increases, the activity of lower brain structures is reduced and the probability for psychotic or impulsive behaviors is enhanced. This assumption is supported by ®ndings that stimulant drugs decrease impulsiveness (Eysenck, 1963; Eysenck & Gudjonsson, 1989) and increase the amplitude of P300 peak (Klorman et al., 1988). Other ®ndings also indicate that impulsiveness is related to psychoticism and extraversion and that these two dimensions are related to lower cortical arousal (Strelau & Eysenck, 1987). The anxiety factor, de®ned as a combination of positive N and negative L, was found independent from the other personality dimensions considered in this study. Anx was sensitive in detecting di€erential HR changes with emotional cueing. The high Anx scorers, as compared to the low Anx ones, were more sensitive to negative emotional cueing by displaying greater HR accelerations in the time interval between negative cue words and target stimuli. There were no di€erences in HR between groups for positive and neutral cued targets. For P300 and behavioural measures no signi®cant di€erences between high and low Anx groups were found. According to Lacey and Lacey's (1970) model, heart rate accelerations occurring during emotional states should be associated with cortical deactivation and inhibited information processing, as predicted by defense reaction. Therefore, the greater HR sensitivity in high Anx subjects for unpleasant cued trials (and not for pleasant trials) found in this study seems compatible with Gray's theory. Gray (1987) considers the arousal system as associated with dorsal noradrenergic bundle, which ascends from the locus coeruleus to innervate forebrain structures. This system seems to be more speci®c than the generalized arousal system regarded by ®rst arousal theories. Applying Gray's theory, our current ®nding of greater HR accelerations to negative stimuli in high Anx subjects may be seen as the product of a compensatory activation of the arousal system to maintain eciency of selective attention and motoric responsiveness during punishment signals or states of stress. This ®nding appears in line with our previous observation on HR changes in high and low emotionally reactive subjects, a temperamental trait highly correlated with the N dimension (De Pascalis et al., 1999).

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