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Looking for trouble? Processing of physical and social threat words in impulsive and premeditated aggression.

Research in the area of human aggression has resulted in the emergence of two major subtypes: an impulsive type that is also sometimes referred to as affective or reactive, and a second type that is variably characterized as premeditated, predatory, proactive, or instrumental (Houston et al. 2004). (1) Impulsive aggression presents as a relatively specific pattern of symptoms including spontaneous rage outbursts and aggressive reactions that are "grossly out of proportion to any precipitating psychosocial stressors" (Stanford et al. 1995, p. 757). Similar patterns of behavior have been characterized as episodic dyscontrol syndrome (Monroe 1970) and Intermittent Explosive Disorder (American Psychiatric Association 2000). Outbursts are usually accompanied by an agitated state, coupled with a lack of concern about potential consequences, and often occur in response to a perceived slight. In contrast, premeditated aggression is characterized by planned or goal-directed aggressive acts committed in a controlled, unemotional manner (Stanford et al. 2003a). Whereas impulsive aggressors are more likely to report experiencing thought confusion during their aggressive outbursts and feelings of remorse afterward, premeditated aggressors report having full control of their behavior, are not remorseful, and tend to commit goal-directed aggressive acts, sometimes for the purposes of social gain and dominance (Barratt et al. 1999).

The differences between impulsive and premeditated aggressors extend well beyond issues of purpose, behavioral control, emotional state, and remorse, as research has consistently shown differences in neurochemistry, neuropsychology, psychophysiology, and treatment efficacy as well (Houston et al. 2004; Scarpa and Raine 2000). While premeditated aggressors appear to be quite similar to normal controls, impulsive aggressors are characterized by verbal and executive function deficits (Stanford et al. 1997; Villemarette-Pittman et al. 2003), and low serotonin as evidenced by CSF metabolites (Linnoila et al. 1989; Linnoila et al. 1983; Roy et al. 1988). Several studies have revealed frontal and temporal deficits in aggressive populations (Kuruoglu et al. 1996; Seidenwurm et al. 1997; Volkow et al. 1995), and when murderers were categorized into predatory and affective subtypes (equivalent to premeditated and impulsive, respectively), abnormally low prefrontal functioning was observed only in the affective murderers (Raine et al. 1998).

Previous research has also consistently demonstrated abnormalities in the P300 (or P3) wave, a positive deflection of the event-related potential (ERP) that occurs approximately 300 milliseconds (ms) after the onset of a stimulus, is maximal at posterior scalp locations (Fz<Cz<Pz), and is frequently used as an indicator of cognitive processing efficiency (Polich 1998). These abnormalities, which have typically involved reduced P3 amplitude, have been observed in aggressive populations, especially those whose aggressive behavior is accompanied by a loss of behavioral control (Branchey et al. 1988; Harmon-Jones et al. 1997; Gao and Raine 2009; Gerstle et al. 1998; Mathias and Stanford 1999). Premeditated aggression, on the other hand, has not been associated with reduced P3 amplitude. In fact, despite their personality pathology, premeditated aggressors tend to appear "normal" on most other measures, such as neuropsychological tests and cognitive psychophysiological measures (Houston et al. 2004; Stanford et al. 2003b; Barratt et al. 1997a; Barratt et al. 1997b). Treatment with anticonvulsant medication significantly reduced the number of aggressive outbursts in impulsive aggression and normalized the P3, but it provided no reduction in aggressive behavior in those who were classified as premeditated and had no effect on their P3 (Barratt et al. 1997b; Stanford et al. 2001a; Stanford et al. 2005).

In terms of personality traits, premeditated and impulsive aggressors share many basic attributes, such as impulsivity, anger, hostility, and verbal and physical aggression (Stanford, Houston, Villemarette-Pittman et al. 2003). However, differences exist as well, particularly in the area of psychopathic traits. Previous work involving the Psychopathic Personality Inventory (Lilienfeld and Andrews 1996), showed that IAs had high levels of Machiavellian egocentrism (i.e. narcissistic exploitation of others), carefree non-planfulness (i.e. lack of forethought and insensitivity to consequences), blame externalization (i.e., rationalizing or blaming others for one's own misbehavior), impulsive nonconformity (i.e., lack of concern for rules or social norms), low levels of stress immunity (i.e., absence of emotional reactions to stressful events), and cold-heartedness (i.e., callousness and lack of guilt) as compared to nonaggressive controls (Helfritz and Stanford 2006). The finding that IAs scored significantly lower on stress immunity and cold-heartedness than did nonviolent controls suggests that IAs may be overly emotional or interpersonally supersensitive, traits that would likely contribute to the origin and/or maintenance of chronic aggression problems. Other research involving callous-unemotional (similar to premeditated) college students showed a distinctly different profile that included heightened stress immunity, cold-heartedness, fearlessness, social potency, and carefree non-planfulness (Wilson et al. 1999). In sum, while callous-unemotional/premeditated aggressors seem to be confident individuals who are fully in control of their behavior, unbothered by stress, and adept at manipulating others in social situations, impulsive aggressors frequently lose control of their behavior, are unusually susceptible to the negative effects of life stressors, and are not particularly effective in social situations.

Cognitive factors such as attentional bias have not been widely studied in aggressive populations, and results have been inconsistent, with some researchers finding attentional bias toward anger-related words (van Honk et al. 2001a) or angry faces (van Honk et al. 2001b) in individuals high in trait anger and others finding this effect only when the task was preceded by an anger-arousing naturalistic insult (Cohen et al. 1998; Eckhardt and Cohen 1997), and still others failing to find significant differences between violent and nonviolent offenders' attention toward aggression words (Smith and Waterman 2003, 2004a, b). Additionally, in a study of college students, Smith and Waterman (2005) found that physical aggression was predictive of the degree of attentional bias toward aggressive words.

Attentional bias has traditionally been assessed using reaction time-based tasks such as the modified Stroop task (e.g., van Honk et al. 2001 a), visual search (e.g., Cohen et al. 1998), or dot probe tasks (e.g., Smith and Waterman 2003); however, in recent years researchers have expanded their approach to include the use of ERPs (Miltner et al. 2005; Thomas et al. 2007; Trippe et al. 2007). The P3 can be an effective way to assess attentional bias from a physiological perspective, as it is an index of attentional allocation (Hillyard and Kutas 1983), and P3 latency has been characterized as a measure of stimulus evaluation time (Gevins and Cutillo 1986). Although reaction time-based tasks are a legitimate way to measure attention, they are dependent on a physical response to a stimulus and the human error that can occur as an individual attempts to execute his or her intended response. In contrast, the P3 presents an opportunity to examine attentional processes in a more direct way by recording the brain activity that accompanies exposure to threatening or aggression-related stimuli; this can potentially remove a layer of "noise," as the P3 is measured immediately when a stimulus is processed, as opposed to reaction time-based tasks, in which measurements occur after the stimulus has been both cognitively processed and responded to by the participant.

The paradigm most often used to elicit the P3 is the oddball task. A standard oddball task typically consists of a low probability target stimulus (e.g., B) embedded within a series of higher probability distractor stimuli (e.g., A), with a target to nontarget stimulus ratio of 20:80. Modified oddball tasks have been used to study information-processing biases to specific categories of word stimuli in populations such as combat veterans with PTSD (Stanford et al. 2001b) and alcoholic inpatients (Hansenne et al. 2003). However, these techniques have not yet been used to assess whether such processing biases may exist in individuals who are physically aggressive.

A large P3 wave, an index of the allocation of information processing resources, is generated when inherently relevant stimuli (e.g., the participant's own name) are presented, even when those stimuli are not task relevant (Berlad and Pratt 1995; Farwell and Donchin 1991; Matsuda et al. 1990). This is consistent with Johnson's (1986) triarchic model of the P3, which also emphasizes the importance of stimulus meaning, both intrinsically and in relationship to the task, and considers stimulus probability and meaning to have independent additive effects on P3 amplitude. Stanford et al. (2001b) study of attentional bias in Vietnam combat veterans with and without PTSD involved two different modified oddball tasks designed to compare processing of trauma-relevant and trauma-irrelevant threat words. Each oddball task included low probability-neutral targets (e.g., household items) and high probability-neutral distractors interspersed with either combat threat (e.g., jungle, ambush, body bags) or social threat (e.g., insult, fail, pathetic) distractor words of low probability. Results showed that veterans with PTSD had enhanced P3 amplitude at frontal electrode sites to combat words but not to social threat words, indicating an attentional bias specific to threat information relevant to their source of trauma.

In conclusion, reduced P3 amplitude to neutral target stimuli has been consistently associated with impulsive aggressive behavior but not with premeditated aggression. The P3 has also been used as an index of attentional bias when enhanced P3 amplitude is observed in response to select stimuli but not to others; however, to date, no psychophysiological research has investigated attentional bias toward threatening stimuli in physically aggressive individuals.

The purpose of the current study was to use the P3 to assess whether information processing biases may exist toward physical and social threat words in physically aggressive individuals and, if so, whether these biases vary between the subtypes of impulsive and premeditated aggression. Enhanced P3 amplitude to threat words in aggressive individuals may be indicative of a selective cognitive bias that could be related to a hostile attributional bias, or tendency to interpret the intent of others as hostile, despite the fact that environmental cues fail to indicate clear intent (Milich and Dodge 1984).

Previous research on attentional bias in other populations has shown that the use of stimuli relevant to individuals' current concerns is an important factor, as attentional biases can be highly specific and dependent on the salience of the stimuli to the individual (Munafo and Stevenson 2003). Due to the high salience of aggressive words for both groups of aggressors, we expected the physical threat words to elicit enhanced P3 amplitude for both impulsive and premeditated aggressors. However, due to personality differences we anticipated that only impulsive aggressors would show a similar exaggerated response to the social threat word category (Helfritz and Stanford 2006). If so, this would indicate that only impulsive aggressors exhibit a cognitive bias toward socially threatening words, and would support the notion that IAs may be overly sensitive to social cues or criticisms whereas PMs are unconcerned with winning the approval of others. Based on our previous work with impulsive aggressors (Gerstle et al. 1998), we did not expect to find group differences in P3 latency and anticipated traditional latency topography (Fz>Cz>Pz; Polich 1998).



Students (N =867) from undergraduate courses at a large private liberal arts university completed screening questionnaires (described below), and those who met criteria for either the premeditated aggressive, impulsive aggressive, or nonaggressive control group were contacted by phone and invited to participate in the study; however, the vast majority of individuals who completed the screening did not qualify for inclusion in any of the groups. Additional exclusionary criteria for all participants included the following: medical/neurological problems, including seizures; history of major head injury (loss of consciousness greater than 5 minutes or requiring medical care); current use of psychoactive medications; left-handedness; first language other than English; and age below 18 or over 25 years. Potential controls were also excluded from participation if they had been the victim of a violent crime, such as physical assault, as research has shown threatening stimuli to be as salient to victims as it is to instigators (Riemann and McNally 1995). Due to the additional complications involved with having to control for phase of the menstrual cycle when measuring the P3 in female participants (Johnston and Wang 1991), along with our desire to recruit the most physically aggressive sample possible, we also excluded women from participation. Sixty-seven male college students between the ages of 18 and 24 years participated. Nine of these participants (aggressors: n =8; controls: n =1) were subsequently excluded from analysis because, although they had appeared to meet criteria during the initial paper-and-pencil screening, their group membership could not be confirmed when the interview version of the Lifetime History of Aggression Questionnaire (LHAQ; Coccaro et al. 1997) was administered in person at the research appointment. The final sample (N =58) was composed of three groups: impulsive aggressors (IAs; n =15), premeditated aggressors (PMs; n =22), and nonaggressive controls (n =21). Participants received extra course credit and a $10 gift card to a local business for their participation.

In order for individuals to be classified as impulsive aggressive (IA), they must have been physically aggressive with another person within the past 12 months (i.e., pushing, grabbing, slapping, hitting, throwing an object at someone, been in a physical fight, bar fight, using a weapon, etc.), obtained a score of 9 or higher on the LHAQ Aggression subscale, (2) obtained an Impulsive/Premeditated Aggression Scales (IPAS; Stanford et al. 2003a) result classifying their aggressive acts as primarily impulsive, and met the following criteria for impulsive aggression (Stanford et al. 1995): (a) Over the past year, the participant must have experienced several discrete episodes of failure to resist aggressive impulses that resulted in serious assaultive acts or destruction of property; (b) the degree of aggressiveness expressed during the episodes must have been grossly out of proportion to any precipitating psychosocial stressors; and (c) the participant must have scored an 8 or greater on the Irritability subscale of the Buss-Durkee Hostility Inventory (Buss and Durkee 1957). The first two criteria described above are also two of the diagnostic criteria for Intermittent Explosive Disorder (American Psychiatric Association 2000), and the third criterion has been associated with chronic difficulties in aggression control (Stanford et al. 1995).

In order for individuals to be classified as premeditated (PM) aggressors, they must have been physically aggressive with another person within the past 12 months, obtained a score of 9 or higher on the LHAQ Aggression subscale, and obtained an Impulsive/Premeditated Aggression Scales (IPAS; Stanford et al. 2003a, b) result classifying their aggressive acts as primarily premeditated; but he or she must NOT have met the first two impulsive aggression criteria as described above.

To qualify for the nonaggressive control group, participants must not have been physically aggressive with another person within the past 12 months and must have obtained a score of 3 or lower on the irritability subscale of the Buss-Durkee Hostility Inventory.

Materials and Procedure

Informed consent was obtained, and all participants completed a battery of self-report measures as part of a larger study and event-related potential (ERP) tasks; the experimental session lasted approximately 3 hours and was followed by debriefing.

Self-Report Measures

Lifetime History of Aggression Questionnaire (LHAQ; Coccaro et al. 1997) The questionnaire form of this instrument was used to assess aggression during the screening process, while a more in-depth interview version was completed with all who decided to participate in the study. Eleven antisocial behaviors since the age of 13 were rated for frequency on a 6-point Likert scale (0=no occurrences', 1 =one event; 2=two or three events; 3 =four to nine events; 4=10 or more events; 5=more events than can be counted). The LHAQ contains three subscales: (a) Aggression--items include verbal aggression, indirect aggression (i.e., aggression directed toward inanimate objects), nonspecific fighting (i.e., whether or not instigated by the participant), physical assault against people (with evidence of intent to harm), and temper tantrums; (b) Antisocial Behavior--items include school disciplinary problems (e.g., suspensions, reprimands), problems with supervisors (e.g., demotions, firings, warnings), antisocial behavior not resulting in police involvement (e.g., selling drugs, prostitution, arson, driving when intoxicated), and antisocial behavior involving the police with arrests or convictions; and (c) Self-Directed Aggression--items include self-injurious behavior and suicide attempts. In Coccaro's original study, the internal consistency of the LHAQ (Cronbach's alpha) was .88 for the Total score, and .87, .74, and .48 for the Aggression, Antisocial Behavior, and Self-Directed Aggression scales, respectively (Coccaro et al. 1997).

Barratt Impulsiveness Scale (BIS-11; Patton et al. 1995) This self-report measure of general impulsiveness consisted of 30 items (e.g., "I make up my mind quickly") that were rated on a 4-point Likert scale (1 =rarely/never, 2=occasionally, 3 = often, 4=almost always/always); the BIS-11 has previously been shown to be internally consistent in college students (Cronbach's alpha=.82; Patton et al. 1995).

Buss-Perry Aggression Questionnaire (BPAQ; Buss and Perry 1992) This 29 item self-report questionnaire was scored on a 5-point Likert scale (1 =extremely uncharacteristic of me to 5=extremely characteristic of me) and yielded four different measures of trait aggression: (a) Physical Aggression (e.g., "Given enough provocation, I may hit another person"), Verbal Aggression (e.g., "When people annoy me, I may tell them what I think of them"), Anger (e.g., "I sometimes feel like a powder keg ready to explode"), and Hostility (e.g., "At times I feel I have gotten a raw deal out of life"). In Buss and Periy's (1992) original study of college students, the internal consistency (Cronbach's alpha) values for the BPAQ were as follows: Physical Aggression=.85, Verbal Aggression=.72, Anger=,83, Hostility=.77, and Total score=.89.

Impulsive/Premeditated Aggression Scale (IPAS; Stanford et al. 2003a) This 30-item self-report questionnaire assessed impulsive and premeditated characteristics of aggressive acts that occurred within the past 6 months; items were rated on a 5-point Likert scale (1 = strongly disagree, 2=disagree, 3= neutral, 4=agree, 5=strongly agree). If an individual endorsed (i.e., agree or strongly agree) a higher percentage of impulsive items (e.g., "When angry, I reacted without thinking") as compared to premeditated items (e.g., "I planned when and where my anger was expressed"), this score (in conjunction with the other screening measures described above) was considered supportive of placement in the impulsive aggressive group. If a higher percentage of premeditated items was endorsed, this supported placement in the premeditated aggression group. In the original IPAS study (Stanford et al. 2003a, b), the internal consistency (Cronbach's alpha) values of the IA and PM scales were .82 and .77, respectively. Additionally, the two scales were not correlated (r=-0.02).

Psychophysiological Measures

Psychophysiological recordings were taken between the hours of 12:00 p.m. and 4:00 p.m. to control for diurnal variations in scalp patterns (Geisler and Polich 1990). Participants were seated in a comfortable chair in a sound and light attenuated chamber. The scalp and mastoids were prepared by the vigorous application of nibbing alcohol followed by a mildly abrasive gel (NuPrep). The participant's head was fitted with a Quick-Cap (Neuroscan) containing 64 electrodes, arranged according to the International 10-20 system with standard and intermediate positions. Electrodes were referenced to an average reference, and four electrooculogram electrodes were affixed near the eyes in order to record horizontal and vertical eye movements that may have contaminated EEG data. An ocular artifact reduction technique was applied to the data offline in order to remove any eye movement contamination.

EEG data were recorded continuously at a sampling rate of 1,000 samples per second and were amplified by SYNAMPS2 amplifiers (Neuroscan). Filter band pass was set at 0.1 Hz to 35 Hz. Impedance for each electrode was maintained at less than 5 kfh Epochs beginning 100 ms prior to stimulus onset and extending to 900 ms poststimulus were created offline.

P3 peak amplitude was determined from baseline (defined as 100 ms prior to stimulus onset). The P3 component of the ERP was defined as the most positive peak occurring between 250 and 450 ms after stimulus onset. Amplitude was measured as the [mu]V (microvolt) deflection from the baseline to peak, and latency was measured as time in ms from stimulus presentation to peak. As is standard in P3 research, we focused on the three midline electrodes (Fz, Cz, and Pz) in order to allow comparison with previous studies on P3 topography, amplitude, and latency (Polich 1998).

Neutral visual oddball task A neutral visual oddball task consisting of rare neutral target words (household items) and frequent neutral distractor words was administered. A randomly ordered block of 20 targets and 80 neutral distractors was repeated and rerandomized once for a total of 200 trials. Participants were asked to press a button with their right index finger whenever they saw a target word. This task was designed to elicit a P3 to the neutral targets and was intended to serve as a baseline to demonstrate reduced P3 amplitude in impulsive aggression. Targets and distractors were equated for length and frequency of use in the English language (Carroll et al. 1971).

Threat word oddball task A modified visual oddball task consisting of the following four word types was administered: neutral targets (20), physical threat distractors (20), social threat distractors (20), and neutral distractors (140). The block was rerandomized and repeated once for a total of 400 trials. Participants were asked to press a button with their right index finger whenever they saw a target word (i.e., item of clothing). As a preliminary caution, potential words for the physical threat (e.g., fight, murder), social threat (e.g., pathetic, stupid), and neutral target (e.g., socks, shirt) categories were rated by undergraduate college students (n =45) for level of aggressiveness and emotionality on a scale of 1 to 9. This was done to ensure that the words chosen for the physical threat category were genuinely considered to be aggressive by college students and to verily that neutral target words were in fact neutral. Neutral distractors were taken from the Affective Norms for English Words (Bradley and Lang 1999) word list, which has been extensively normed for valence. Words chosen for use in the oddball task were equated for length and frequency of usage in the English language (Carroll et al. 1971). This task was expected to elicit a P3 to each category of low probability stimuli and was designed to enable a comparison of attentional resource allocation to different types of threat stimuli (physical and social) and neutral targets. As a post hoc check, participants rated the physical threat, social threat, and neutral target words for aggressiveness after completing the ERP tasks. As research has shown that exposure to aggression measures can affect performance on threat word tasks, all aggression-related measures were given after the ERP tasks had been completed (Riemann and McNally 1995).

Statistical Analysis

Univariate analyses of variance (ANOVAs) and post hoc t tests were used to compare impulsive aggressors, premeditated aggressors, and nonaggressive controls on demographic variables and self-report questionnaire measures. For all univariate ANOVAs and post hoc t tests, the Bonferroni inequality was used to control for Type I error rate inflation.

A one-between (group) and one-within (electrode site) repeated measures ANOVA was conducted in order to assess P3 amplitude and latency to target stimuli at midline electrodes for the neutral word task. A one-between (group) and two-within (electrode site and stimulus type) repeated measures ANOVA was used to assess P3 amplitude and latency at midline electrodes for the threat word task. For all repeated measures analyses, the Geisser-Greenhouse (Geisser and Greenhouse 1958) conservative F test was used as a correction to guard against violations of the sphericity assumption.


Demographic Information

Univariate analyses of variance (ANOVAs) showed that age and education did not significantly differ between the groups (see Table 1), while controls' self-reported cumulative grade point averages (GPAs) were significantly higher than those reported by premeditated aggressors, F(2, 55) =5.28,p=.008, partial [[eta].sup.2]=0.161, power =0.815, as indicated by ANOVA and post hoc t tests.

Measures of Aggression and Impulsivity

Univariate ANOVAs were conducted on the four scales of the Buss-Perry Aggression Questionnaire (BPAQ) and the total score, using the Bonferroni inequality to maintain a familywise (n =5) alpha of 0.05. Significant differences were found on all subscales: Physical Aggression, F{2, 55) =29.01, p[less than or equal to] .001, partial [[eta].sup.2]=0.513, power =1.00; Verbal Aggression, F(2, 55) = 16.01, p [less than or equal to].001, partial [[eta].sup.2]=0.368, power =0.99; Anger, F(2, 55) =17.34, p [less than or equal to] .001, partial [[eta].sup.2]=0.387, power = 1.00; Hostility, F(2, 55) =16.85, p =.001, partial [[eta].sup.2]=0.380, power = 1.00; and BPAQ total score, F(2.,55) =36.43, p [less than or equal to] .001, partial [[eta].sup.2]=0.570, power =1.00. Post hoc t tests revealed that both groups of aggressors scored significantly higher than controls on all four subscales of the BPAQ and the total score (see Table 2).

Using the Bonferroni inequality to maintain a familywise (n =4) alpha of 0.05, univariate ANOVAs were conducted on the LHAQ (Interview Format) and its three subscales, revealing significant differences for the Aggression, F(2, 55) = 128.39, p [less than or equal to] .001, partial [[eta].sup.2] = 0.824, power =1.00 and Antisocial Behavior, F(2, 55) =13.62, p [less than or equal to] .001, partial [[eta].sup.2]= 0.610, power =1.00, subscales and the total score, F(2, 55) =79.21, p [less than or equal to] .001, partial [[eta].sup.2]=0.742, power =1.00. No significant group differences were found for the Self-Directed Aggression subscale.

Post hoc t tests showed that on the LHAQ Aggression subscale, IAs scored significantly higher than PMs, who, in turn, scored significantly higher than controls. Both groups of aggressors scored significantly higher than controls on the Antisocial subscale and LHAQ total score.

A univariate ANOVA of the BIS-11 total score, F(2, 55) =9.20, p [less than or equal to] .001, partial [[eta].sup.2]=0.251, power =0.970, and post hoc t tests revealed that IAs scored significantly higher than both PMs and controls.3

Psychophysiological Measures

Neutral Word Task

Amplitude of the P3 component of the event-related potential (ERP) at midline electrodes (Fz, Cz, Pz) was analyzed using a one-between (group) and one-within (electrode site) repeated measures ANOVA for the neutral word task. Only trials in which the participant responded correctly were included in the averages (see Fig. 1). Results showed no significant interactions or between group differences for neutral target P3 amplitude; however, a main effect for electrode site was found, F(1.51, 78.45) =48.03, p [less than or equal to] .001, partial [[eta].sup.2]=0.480, power =1.00. Follow-up contrasts showed significant (p [less than or equal to] .001) differences in P3 amplitude between sites Fz (M=-0.04, SE=.331) and Pz (M =4.02, SE = 0.389) and between sites Cz (M =0.124, SE =0.315) and Pz (see Table 3).

Repeated measures ANOVA revealed a significant group x site interaction, F(3.75, 97.61) =2.94, p=.027, partial [[eta].sup.2] = 0.101, power =0.751, for P3 latency on the neutral word task. Follow-up contrasts indicated a significant difference in P3 latency between sites Fz and Pz, t(20) = 2.72, p =.013, for the control group but no within-group differences were found for the aggressive groups.

Threat Word Task

Amplitude of the P3 component of the event-related potential (ERP) at midline electrodes (Fz, Cz, Pz) was analyzed using a one-between (group) and two-within (stimulus type, electrode site) repeated measures ANOVA for the threat word task. Only trials in which the participant responded correctly were included in the averages. Results revealed a significant group x stimulus type interaction, F(3.96, 102.96) =2.53, p=.045, partial [[eta].sup.2]=0.089, power =0.697. Follow-up contrasts showed a significant within-group difference for the control group between physical threat and neutral target words and between social threat and neutral target words, but revealed no significant within-group differences for either aggressive group (see Fig. 2).

Repeated measures ANOVA revealed a significant group x site interaction, F(3.82, 99.20) =3.07, p=.021, partial [[eta].sup.2] = 0.106, power =0.778, for P3 latency on the threat word task. Within the control group, follow-up contrasts showed significant differences in P3 latency between sites Fz and Cz, between sites Cz and Pz, and between sites Fz and Pz. Within the IA group, follow-up contrasts showed a significant latency difference between sites Cz and Pz; however, no significant latency differences were found within the PM group (see Fig. 3). For a comparison of the within-group grand-average waveforms for each stimulus type at electrode Pz, see Fig. 4.

As a check, after participants had completed the ERP tasks they were asked to rate the physical threat, social threat, and neutral target words for aggressiveness on a scale of 1 to 10. Univariate ANOVAs showed no significant group differences for any of the word types, indicating that aggressive and nonaggressive participants perceived each of the word groups similarly (see Table 4). Univariate ANOVAs were used to analyze omission (failure to respond to target stimuli) and commission (responding to nontarget stimuli) errors for each of the word tasks; no significant group differences were found for any error type.


To our knowledge, this study was the first to compare impulsive and premeditated aggression in a college sample and to use psychophysiological measures to explore attentional bias toward threat in physically aggressive individuals. These data are part of a larger study designed to compare and contrast the personality and psychopathology of the aggressive subtypes; however, the main goal of the current research was to investigate whether differences exist in the processing of physical and social threat stimuli, as increased attention to such cues could contribute to the maintenance of chronic aggression.

Demographic Information

The three groups did not differ on demographic variables such as age and education; however, premeditated aggressors did report slightly less academic success than controls, as indicated by cumulative GPA. It remains unclear whether this difference was related to actual ability or to motivational factors, the latter being the more likely explanation in an antisocial sample.


Anger, Aggression, and Impulsivity

As expected, both aggressive groups scored significantly higher than controls on measures of aggression such as the BPAQ and LHAQ, indicating that the screening procedures successfully formed the appropriate groups. One unexpected finding was the difference between impulsive and premeditated aggressors on the LHAQ aggression subscale; however, one could argue that since a large proportion of that subscale (40%) is made up of questions regarding behaviors highly characteristic of impulsive aggressors but much less characteristic of premeditated aggressors (e.g., throwing and breaking things or slamming doors), it is not so surprising that IAs would score higher than PMs. This explanation is supported by the fact that no differences between the aggressive subtypes were found on any of the other nine measures of aggression that were administered in this study.

P3 Amplitude and Latency

For the neutral word task, a main effect of site showed that typical P3 topography was observed (Fz<Cz<Pz). Contrary to expectations, IAs did not display a significant deficit in P3 amplitude to target stimuli in the neutral word task. Although it is unclear why this occurred, previous work in which decreased P3 amplitude had been observed in IAs as compared to controls used standard tasks that were very simple and consisted of a few repeating symbols, such as letters A and B. The present study used more complex word stimuli, which were repeated only once and resulted in very small P3 amplitudes in all three groups. Group means for observed P3 amplitude at Pz ranged from approximately 3 to 4.5 microvolts for the neutral word task, whereas the P3 amplitudes in the studies that found deficits in IAs typically fell within the 10 to 15 microvolt range for normal controls (Barratt et al. 1997b; Gerstle et al. 1998; Houston et al. 2004; Stanford et al. 2003a, b). It is likely that the neutral word task produced small amplitudes in all groups because of the increased task difficulty, which has been shown to attenuate P3 amplitude (Kok 1997). Stanford et al. (2001b) used word stimuli in their study of Vietnam veterans with and without PTSD, and they also reported small P3 amplitudes that are comparable to the present study. Additionally, a recent meta-analysis of the P3 in antisocial and psychopathic individuals concluded that P3 amplitude is dependent on task demands, with more complex tasks being less likely to lead to attenuated P3 amplitude in psychopathic individuals; this may be related to their increased sensation-seeking tendencies, as complex tasks are more effective than monotonous standard oddball tasks at holding their attention (Gao and Raine 2009).


P3 latency to targets in the neutral word task did not follow the expected topography (Fz>Cz>Pz); only the control group displayed traditional topography, with the shortest latency at Pz. Both aggressive groups' longest latencies occurred at Pz, indicating that aggressors took longer to evaluate target stimuli, a potential sign of less efficient cognitive processing as compared to the control group (Polich 1998). This result is consistent with Bond and Surguy's (2000) finding that prolonged P3 latency to target stimuli was related to aggression and hostility, and especially to suspicion and resentment.

As in the neutral word task, attenuated P3 amplitudes were obtained for all groups in the threat word task. Although results deviated from expectations in that the aggressive groups did not show enhanced P3 amplitude to threat words, an intriguing pattern of within-group differences was found in relation to stimulus word type. Controls showed a pattern of processing characterized by enhanced P3 amplitude to both categories of threat words as compared to neutral target words. In contrast, IAs showed P3 amplitudes that were relatively equal across physical threat, social threat, and neutral target words, as did PMs, indicating an absence of amplitude enhancement in response to potentially threatening stimuli in both aggressive groups. In sum, both the physical and social threat stimuli were threatening enough to attract the attention of the nonaggressive controls, but the aggressive groups processed them as if they were neutral, potentially indicating abnormal processing of affective stimuli. This result is especially interesting in light of the fact that all groups rated the physical threat words as being equally aggressive, thus precluding the idea that the groups simply interpreted the threat value of the words differently. When potentially threatening stimuli are present in the environment, it is important to allocate sufficient attention toward them so that a response can be quickly activated if necessary. For example, research using visual search tasks with normal college samples has demonstrated that angry faces are consistently detected more quickly and accurately than other faces, indicating that it may be adaptive and quite natural to orient attention toward threat cues (Fox et al. 2000; Ohman et al. 2001). This adaptive and natural response to threat was demonstrated by the controls in our sample in their P3 response to the aggressive words; however, the aggressors instead showed a maladaptive pattern in which potential threats did not seem to command their attentional resources as they should have.



Results of P3 latency for the threat word task revealed a similar pattern for IAs and controls in which the shortest latency occurred at Pz. PMs displayed the opposite pattern, indicating that they took longer to process deviant stimuli than the other groups did, and were therefore potentially less efficient.

General Conclusions

Although these results are tentative and should be interpreted with caution, the idea that emotional processing deficits may occur in aggressive individuals is consistent with recent research in this area. A study of facial expression recognition compared the performance of incarcerated violent and nonviolent offenders and found deficits only in the violent offenders (Hoaken et al. 2007). Additionally, a recent study of the functional neuroanatomy of impulsive aggression revealed a decoupling of the amygdala and the orbitofrontal cortex when individuals with Intermittent Explosive Disorder viewed angry faces (Coccaro et al. 2007), a stimulus that is known to possess a strong threat value (Dimberg and Ohman 1996). More specifically, the OFC, which is involved in the appraisal of emotionally salient stimuli, showed a dampened response instead of inhibiting the amygdala as it normally would (Coccaro et al. 2007). Additionally, Schippell et al. (2003) used a dot probe task to explore the relationship between reactive and proactive aggression and attentional bias to threat stimuli in children. As in the present study, they expected to find an association between reactive aggression and increased attention to social threat cues; however, they instead found a suppression of attention to these cues. Although this result was not seen for the physical threat words used in Schippell's study, the content of this word list differed from that in our study, as it was more related to illness and injury than to aggression. It remains unclear why suppressed attention to threat was limited to reactive (or impulsive) aggression in Schippell's work but not in ours.

Limitations and Future Research

Although results of the present study are promising, several potential limitations should be discussed. First, although the present sample of aggressors met the criteria for chronic physical aggression, this was a college sample obtained from a large private liberal arts university, and the level of aggression reported was not as severe as that of some other populations studied in the general aggression literature, so the results may not generalize. Additionally, this sample was also presumably higher in socioeconomic status, although we did not directly measure this. Second, this sample did not include female aggressors and, consequently, results also may not generalize to women. A third limitation of the study was the length of the threat word task; it was 16 minutes long, at least twice the length of the typical ERP task. The cumbersome length of this task may have affected the results by depleting motivational resources. A fourth limitation was the lack of a simple, standard P3 task (e.g., As and Bs), which could have facilitated a more direct comparison between the results of this study and the ones that preceded it. The exclusive use of tasks involving complex word stimuli leaves one wondering whether and how these groups might have differed under more standard conditions.

Another potential limitation is that our threat stimuli were presented in isolation, without context, resulting in poor ecological validity. This may have affected the way the threat words were processed; however, this concern is minimized by the nonaggressive control group's clearly heightened response to both the physical and social threat words. The control group showed a typical, adaptive response to threat in this task, whereas the aggressive groups did not.

The present findings seem to point future research in the direction of emotional processing. Based on the results of the threat word task, abnormalities may exist in both impulsive and premeditated aggressors, and this avenue should be more thoroughly explored. Future research should involve multiple oddball tasks of varying complexity for comparison purposes, and varied stimulus types, such as angry faces, which have a potent inherent threat potential and are not dependent on verbal processing. Although neither group seems to be "looking for trouble" in terms of allocating increased attention toward threatening stimuli, by not giving potential danger the attention it deserves, both aggressive groups appeared to process threat cues less efficiently than controls did.

DOI 10.1007/s40732-014-0106-z

Published online: 3 December 2014

Acknowledgments The authors would like to thank Brian K. Rundle (Baylor University) for his technical assistance. This research was funded by the Dreyfus Health Foundation.


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Laura E. Helfritz-Sinville is now at the College of St. Benedict/St. John's

University, Collegeville, Minnesota.

L. E. Helfritz-Sinville * M. S. Stanford

Department of Psychology and Neuroscience, Baylor University, Waco, TX, USA

L. E. Helfritz-Sinville ([mail])

Department of Psychology, College of St. Benedict/St. John's University, 130 Peter Engel Hall, Collegeville, MN 56321,


e-mail: LSinville@CSBSJU.EDU

(1) IA=impulsive aggression; PM=premeditated aggression; LHAQ=Lifetime History of Aggression Questionnaire; BPAQ=Buss-Perry Aggression Questionnaire; BIS=Barratt Impulsiveness Scale; IPAS=Impulsive and Premeditated Aggression Scale.

(2) This cutoff score represented one standard deviation below the mean (12.4) obtained by impulsive aggressors in Helfritz and Stanford (2006), as an attempt to maintain continuity regarding the classification of aggression between the two studies.

(3) The impulsive and premeditated groups also differed on a number of other personality and psychopathology measures that extend beyond the scope of this paper and will be presented in detail elsewhere (Helfritz-Sinville and Stanford, manuscript in preparation).
Table 1 Demographic Information

                 Impulsive      Premeditated       Nonaggressive
                 Aggressors     Aggressors         Controls

Variable           M      SD        M        SD      M      SD

Age              19.40   0.83   19.36       1.33   19.38   1.12
Education        12.93   0.80   12.64       0.79   12.62   0.86
Cumulative GPA   2.91    0.55    2.76 (a)   0.67   3.30    0.43

Note. GPA was measured on a 4.0 scale

(a) denotes significant difference from controls (p<.01)

Table 2 Measures of Aggression and Impulsivity

                Impulsive            Premeditated
                Aggressors           Aggressors

Measure         M            SD      M                 SD

Buss-Perry Aggression

Physical        57.58 (c)    11.06   57.82 (c)         8.83
Verbal          54.79 (b)    10.00   59.74 (c)         9.33
Anger           56.19 (c)    9.45    52.44 (c)         8.28
Hostility       54.18 (c)    8.58    49.70 (c) 10.93   37.77
Total Score     58.16 (c)    10.74   56.68c            8.90

Lifetime History of Aggression
Questionnaire (Interview Fonnat)

Aggression      17.33 (cd)   3.54    14.41 (c)         3.03
Antisocial      5.13 (c)     3.31    5.14 (c)          3.85
Self-Directed   1.20         2.21    0.32              0.89
Total Score     23.67 (c)    6.97    19.86 (c)         5.53

Barratt Impulsiveness Scale-11

Total Score     57.84 (cd)   10.09   48.90             9.91


Measure         M         SD

Buss-Perry Aggression

Physical        39.78     6.07
Verbal          44.60     7.47
Anger           40.90     7.53
Hostility       6.67
Total Score     36.79     7.00

Lifetime History of Aggression
Questionnaire (Interview Fonnat)

Aggression      3.24      2.07
Antisocial      0.86      1.24
Self-Directed   0.10      0.30
Total Score     4.19      2.25

Barratt Impulsiveness Scale-11

Total Score     45.25     6.19

Note. All BPAQ and BIS scores represent T scores

(a) denotes significant difference from controls
(p [less than or equal to] .05);

(b) denotes significant difference from controls
(p [less than or equal to] 01);

(c) denotes significant difference from controls
(p [less than or equal to] .001);

(d) denotes significant difference between the
aggressive groups (p<.05)

Table 3 P3 Amplitude and
Latency to Target Stimuli in
Neutral Word Task

                 Impulsive        Premeditated     Non-Aggr.
                 Aggressors       Aggressors       Controls

                   M       SD       M       SD        M        SD

P3 Target
Amplitude (pV)
  Fz (a)          -0.50   2.59    -0.05    2.44      0.44      2.31
  Cz (a)           0.10   2.24     0.27    2.46      0.00      2.22
  Pz               3.37   3.07     4.12    2.28      4.57      3.15

P3 Target
Latency (ms)
  Fz             371.47   49.41   347.58   57.48   394.19 (b)  56.33
  Cz             366.67   61.71   359.26   81.26   369.76      56.25
  Pz             398.07   46.75   374.58   58.62   348.71      54.06

Note. [micro]V=microvolts from baseline; ms= milliseconds following
stimulus presentation

(a) denotes significant difference from Pz as a site main effect
(p [less than or equal to] .001); (b) denotes significant
difference from Pz as a within-group effect
(p [less than or equal to] .01)

Table 4 Word Ratings and
Behavioral Data for ERP Tasks

                            Impulsive    Premeditated   Nonaggressive
                            Aggressors   Aggressors     Controls

Variable                    M      SD     M      SD     M      SD

Physical Threat            7.46   0.95   7.59   0.85   7.53   0.71
Social Threat              4.31   1.60   3.61   1.51   3.30   1.44
Neutral Target             1.20   0.37   1.24   0.47   1.19   0.41
Neutral Word Task Errors
  Omission Errors          2.53   1.92   2.95   2.20   3.81   2.86
  Commission Errors        1.93   2.55   1.37   1.16   1.62   1.20
Threat Word Task Errors
Omission Errors            5.67   3.64   4.95   4.09   4.76   3.36
Commission Errors          0.67   1.05   0.47   0.70   0.80   1.01

Note. No significant group
differences were found for word
ratings or ERP task errors
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Author:Helfritz-Sinville, Laura E.; Stanford, Matthew S.
Publication:The Psychological Record
Article Type:Clinical report
Date:Jun 1, 2015
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