Aim and hypotheses

There is ample evidence that individuals with antisocial behaviour show impaired performance on measures of executive functioning. However, it should be noted that the frontal lobe positions have been relatively underspecified, typically, they do not distinguish between different forms of executive dysfunction or different regions of the prefrontal cortex. In addition, it remains unclear whether executive dysfunction relates to antisocial behaviour more broadly or to other characteristics, such as aggression, which may contribute to antisocial behaviour. Therefore, the purpose of the current study is to examine functional neuropsychological deficits (i.e., deficits with no identified organic aetiology such as head injury), namely executive functions, in impulsive-aggressive and premeditated-aggressive individuals, as well as controls. A number of well-validated tests of executive function were chosen to assess the performance of the groups across a range of executive abilities.

While previous studies on aggression have demonstrated prefrontal deficits more broadly, it is the aim of the current study to focus on the separable role of the dorsolateral prefrontal system to determine if deficits in this region are related to impulsive-aggression and/or premeditated aggression. As previously mentioned, the orbital region of the prefrontal cortex has been found to be related to emotional regulation and impulsivity, thereby increasing susceptibility to aggressive impulses,

whereas the dorsolateral region of the prefrontal cortex has been found to be primarily responsible for aggressive behaviour due to impairments in executive functioning (Giancola, 1995). The focus of this study is thus on the role of the dorsolateral prefrontal cortex through executive functions in the expression of impulsive- and premeditated-aggression.

Based on the research outlined above, it is hypothesised that in comparison to controls, executive functioning deficits (e.g., planning, problem-solving, inhibition, cognitive flexibility, set-shifting) will be present in impulsive-aggressive individuals, given their hostile impulsive reaction in response to provocation which is

demonstrated without forethought or planning (Giancola, 2000). This is in contrast to premeditated-aggression, characterised primarily by planned and controlled

aggressive actions directed at attaining a particular goal. By definition, premeditated- aggression is characterised by intact planning abilities and the cognitive regulation of behaviour. It is therefore expected that premeditated-aggressive individuals will not demonstrate executive functioning deficits in comparison to controls.

5.8 Method

5.8.1 Participants

An initial pool of 484 students from the University of Tasmania was screened using the Aggression Questionnaire – Short Form (BPAQ-SF: Bryant & Smith, 2001). Aggression scores were non-normally distributed, with skewness of .796 (SE = .115) and kurtosis of .375 (SE = .23).

Based on questionnaire responses, 100 participants (female = 68, male = 32) were selected and placed into one of two groups; aggressive (n = 70), and non-

(SD = 7.43) above the mean (M = 24.14) on the BPAQ-SF for the aggressive group (BPAQ-SF = 31) and one standard deviation below the mean for the control group (BPAQ-SF = 17). The aggression scores differed significantly between the aggressive group (M = 37.59, SD = 5.75) and control group (M = 15.2, SD = 1.73), F(1, 99) = 435.93, MSE = 10523.52, p<.001, 2 _{= .816.}

The aggressive group was further divided into predominantly impulsive- aggressive and predominantly premeditated-aggressive using the Impulsive- Premeditated Aggression Scale (IPAS; Stanford, Houston, Mathias, Villemarette- Pittman, Helfritz & Conklin, 2003a). The IPAS was developed with 15 items related to impulsive-aggression and 15 items to premeditated-aggression. However, based on the original factor analysis, it is unclear which items specifically refer to each subtype as the item principal components analysis identified three factors (impulsive

aggression, premeditated aggression, familiarity with target/remorse/agitation), rather than the proposed two. Consequently, a series of items were selected which had clear face validity as reflecting the theoretical constructs of impulsive- and premeditated- aggression. From these, only those that shared variance to form clear impulsive- aggressive and premeditated-aggressive in the four factor analyses (Haden, Scarpa & Stanford, 2008; Kockler, Stanford, Nelson, Meloy & Sanford, 2006; Mathias et al., 2007, Stanford et al., 2003a) conducted on the scale to date were selected, and only if they obtained loadings greater than 0.4 on three of the four analyses. This identified eight impulsive and nine premeditated items (see Table 5.1).

Table 5.1

The Impulsive-Premeditated Aggression Scale (Stanford et al., 2003a)

Impulsive Items

1. I became agitated or emotionally upset prior to the acts* 2. I feel I lost control of my temper during the acts*

3. I consider the acts to have been impulsive* 4. When angry I reacted without thinking*

5. I usually can‟t recall the details of the incidents well* 6. I feel some of the incidents went too far*

7. My behaviour was too extreme for the level of provocation* 8. I was in a bad mood the day of the incident*

9. I feel I acted out aggressively more than the average person during the last 6 months 10. I knew most of the persons involved in the incidents

11. I typically felt guilty after the aggressive acts 12. I was concerned for my safety during the acts 13. I was in control during the aggressive act

14. I understood the consequences of the acts before I acted 15. I was confused during the acts.

Premeditated Items

1. I think the other person deserved what happened to them during some of the incidents* 2. I am glad some of the incidents occurred*

3. Some of the acts were attempts at revenge*

4. I feel my actions were necessary to get what I wanted* 5. I felt my outbursts were justified*

6. I wanted some of the incidents to occur*

7. I planned when and where my anger was expressed*

8. Prior to the incidents, I knew an altercation was going to occur* 9. Sometimes I purposely delayed the acts until a later time*

10. The act led to power over others or improved social status for me 11. I was under the influence of alcohol or other drugs during the acts 12. Anything could have set me off prior to the incident

13. I felt pressure from others to commit the acts

14. The acts were a „release‟ and I felt better afterwards

15. My aggressive outbursts were usually directed at a specific person

Participants were placed into either predominantly impulsive-aggressive or predominantly premeditated-aggressive if there was a difference of 25% or greater between their scores on the two subscales, based on the methods of Andreasen and Olsen (1982) and Slaghuis and Bakker (1995). This method led to the exclusion of 15 participants from the 70 aggressive individuals initially identified. The final sample consisted of 38 impulsive-aggressive, 17 premeditated-aggressive and 30 control participants. The number of males and females in each group is shown in Table 5.2.

Table 5.2

Number of males and females in the three participant groups and total sample

Impulsive-

Aggressive Premeditated-Aggressive Control Total

Males 9 11 9 29

Females 29 6 21 56

Mean aggression scores on the BPAQ-SF for the three participant groups are shown in Table 5.3. There was a significant difference in aggression scores between the three groups, F(2, 84) = 189.68, MSE = 4782.43, p<.001, 2 = 822. Post hoc Tukey tests indicated that the impulsive-aggressive and premeditated-aggressive groups had significantly higher aggression scores than the control group (ps < .05). There were no significant differences in BPAQ-SF scores between the males and females in the impulsive-aggressive group, F(1, 37) = .33, MSE = 9.94, p = .57, 2 ₌

.009, premeditated-aggressive group, F(1, 16) = .2, MSE = 10.59, p = .66, 2 _{= .013,}

group, males had significantly higher aggression scores than females, F(1, 29) = 10.3, MSE = 31.56, p = .003, 2 _{= .269.}

Participants‟ ages ranged from 17 to 30 years with a mean age of 19.89 years (SD = 2.56). Mean ages for each participant group are presented in Table 5.3. There was no significant difference in age between the three participant groups, F(2, 84) = .15, MSE = .98, p = .86, 2 _{= .004.}

Inclusion into this study required all participants to be between 17 and 30 years of age, speak English as their first language and have no history of neurological conditions or head injury. Head injury was defined as being knocked unconscious for any period of time, having been diagnosed with concussion by a physician, or having suffered trauma to the head severe enough to require medical attention. Participants were also excluded if they scored lower than 8 (scaled score) on the Wechsler Adult Intelligence Scale – Third Edition (WAIS-III; Wechsler, 1997) Vocabulary and Digit Span subtests which were completed during the testing sessions to rule out a general cognitive or memory deficit.

Table 5.3

Mean (and standard deviation) scores on the Aggression Questionnaire – Short Form and ages for the three participant groups and total sample

Impulsive-

Aggressive Premeditated-Aggressive Control Total

BPAQ-Revised 37.47 (5.47) 38.18 (7.23) 15.50 (2.08) 29.86 (11.77) Males 36.56 (4.25) 38.82 (6.97) 17.00 (1.12) 31.34 (10.94) Females 37.76 (5.83) 37.17 (8.06) 14.76 (1.95) 29.07 (12.24) Age 19.87 (2.71) 19.95 (1.97) 20.07 (2.72) 19.89 (2.56)

5.8.2 Materials 5.8.2.1 Questionnaires

Aggression Questionnaire – Short Form (BPAQ-SF: Bryant & Smith, 2001). For the purpose of selecting participants who were characteristically aggressive, the BPAQ-SF was selected. The BPAQ-SF, a condensed version of the original 29-item Buss-Perry Aggression Questionnaire (BPAQ; Buss & Perry, 1992), is a 12-item self- report measure that records aggressive feelings and behaviours. Items on both forms of the questionnaire load onto four dimensions of aggression: physical aggression, verbal aggression, anger and hostility. Buss and Perry propose that each subscale represents a different element of aggression; the physical and verbal aggression subscales reflect the instrumental or motor behavioural elements of aggression, the hostility subscale reflects the cognitive elements of aggression, while anger reflects the emotional or affective elements and connects the cognitive and behavioural elements.

The BPAQ-SF includes 12 items from the BPAQ, assessed using a 5-point Likert scale, ranging from 1 (very unlike me) to 5 (very like me). In a study comparing the two measures, Bryant and Smith (2001) found comparable internal consistency (alpha coefficients) among the factors on the measures (Physical

Aggression, .79, .80; Verbal Aggression, .83, .80; Anger, .76, .76; and Hostility, .75, .70). The BPAQ-SF shows similar factor loadings for males and females (Bryant & Smith, 2001). Diamond, Wang and Buffington-Vollum (2005) further investigated the BPAQ-SF with a sample of male offenders incarcerated in a psychiatric prison

hospital. The four-factor structure was confirmed with this sample; however,

exchanging one item on the Bryant and Smith Anger scale, “I flare up quickly and get over it quickly”, with “Sometimes I feel like a powder keg about to explode”

improved the fit of the model and increased the reliability of that scale. Reliabilities were comparable to the original form of the BPAQ when corrected for attenuation. The authors of the original BPAQ (Buss & Perry, 1992) report strong internal consistency for each of the four subscales and total aggression scores, with alphas ranging from .72 (verbal aggression) to .89 (full score). Test-retest correlations were also sound, ranging from .72 to .80, indicating stability over time. Correlations between self-report and peer nomination were significant, indicating strong

reliabilities for individuals to self-report their aggressive traits. These findings have been replicated in many studies, finding internal consistency and stability over time for the measure (e.g., Garcia-Leon et al., 2002; Harris, 1997; Williams, Boyd, Cascardi & Poythress, 1996). Further factor analyses have found similar scale structure to that originally claimed for the questionnaire (Harris, 1997).

The Impulsive-Premeditated Aggression Scale (IPAS: Stanford et al., 2003a). The IPAS is a 30-item, self-report questionnaire that classifies an individual‟s

aggressive behaviour as predominantly impulsive or predominantly premeditated in nature. Participants are asked to consider their aggressive acts during the last six months and complete the IPAS in relation to those acts. Of the 30 items, 15 items focus on impulsive aggression characteristics such as “when angry I reacted without thinking”, and 15 items focus on premeditated aggression characteristics, such as “I planned when and where my anger was expressed”. The items are scored on a 5-point Likert scale (5 = strongly agree, 4 = agree, 3 = neutral, 2 = disagree, 1 = strongly disagree). The content of the scales are based on previous scales and studies that have attempted to differentiate impulsive and premeditated aggressive participants (Barratt et al., 1999; Barratt et al., 1997b; Heilbrun et al., 1978; Heilbrun, Knopf & Bruner,

1976; Linnoila et al., 1983; Stanford, Greve & Dickens, 1995; Stanford et al., 1997; Virkkunen, De Jong, Bartko & Linnoila, 1989b; Vitiello et al., 1990).

Stanford et al. (2003a), in their study of men referred for aggression problems, found that that the IPAS demonstrated adequate reliability coefficients (Cronbach‟s αs = .77 for the impulsive scale and .82 for the premeditated scale). The impulsive and premeditated scales were not significantly correlated (r = -.02). The authors also reported strong construct and concurrent validity for the IPAS scales. These findings have been replicated in later studies, finding adequate internal consistency in a forensic sample (impulsive α = .72; premeditated α = .81) (Kockler et al., 2006) and in treated opiate-dependent individuals (impulsive α = 74; premeditated α = .75) (Conner, Houston, Sworts & Meldrum, 2007). Test-retest analyses also indicate good stability, with impulsive and premeditated correlation coefficients .63 and .70

respectively. Also consistent with prior studies of the IPAS, the impulsive and

premeditated scales were found to be poorly correlated, supporting the conception that these scales assess different types of aggression (Conner et al., 2007).

The I7 Impulsivity Questionnaire (Eysenck, Pearson, Easting & Allsopp, 1985). The I7 Impulsivity Questionnaire is a 54-item self-report measure which consists of three subscales: impulsiveness, venturesomeness and empathy. High reliability is reported for each of the subscales for both males and females, with alpha coefficients for impulsivity and venturesomeness reported to be around .80 and empathy at .69. A moderate correlation was found between impulsiveness and venturesomeness (r = .38), reflecting the association between the two subscales in terms of a combined impulsivity trait. The authors conclude that this self-report measure robustly assesses three important characteristics in impulsivity research: impulsiveness, venturesomeness, and empathy. It is the inclusion of empathy that

makes this scale of further relevance for the current investigation into aggression, as lack of empathy can be a defining characteristic of premeditated aggression (Meloy, 1997).

5.8.2.2 Executive function measures

The Delis-Kaplan Executive Function System (D-KEFS; Delis, Kaplan & Kramer, 2001). The D-KEFS is a set of nine standardised tests for assessing executive functions in children and adults. The tests measure a range of verbal and non-verbal executive functions, with each test designed to stand alone or be administered with others from the battery. These tests are predominantly an updated version of

commonly used stand-alone tests of executive functioning with better standardisation and quantitative error scoring. Each of the nine tests were standardised on over 1700 children and adults aged nine to 89 years. Two subtests from the D-KEFS were chosen for the current study; Verbal Fluency Test and the Trail Making Test.

D-KEFS Verbal Fluency Test. The D-KEFS Verbal Fluency Test is modelled on the Controlled Oral Word Association Test (COWAT) which was developed by Benton and his colleagues (Benton & Hamsher, 1976; Spreen & Benton, 1969). The Verbal Fluency Test is comprised of three conditions; letter fluency, category fluency and category switching. Only letter fluency was chosen for the current study given its sensitivity to frontal involvement (Benton, 1968). In this task, the participant is asked to name in 60 seconds as many words as they can that begin with a specified letter over three trials (F, then S, then A). The participant is constrained by two rules: words cannot include the names of people, places, or numbers, and they cannot provide grammatical variants of previous responses (e.g., take, and then taking, takes).

D-KEFS Trail Making Test. The D-KEFS Trail Making Test involves a series of five conditions: visual scanning, number sequencing, letter sequencing, number- letter switching and motor speed. In all five conditions the stimuli are spread over an 11 x 17-inch area, which provides longer trails and more interference stimuli than the traditional Trail Making Test (Delis et al., 2001). In the Visual Scanning condition, participants are required to cross out all the 3s that appear on the response sheet, which are mixed among a collection of other numbers and letters. In the Number Sequencing condition, participants draw a line connecting the numbers 1-16 in order, with distracter letters appearing on the same page. The Letter Sequencing condition requires participants to connect the letters A through P, with distracter numbers present on the same page. In the Number-Letter Switching condition, participants switch back and forth between connecting numbers and letters (i.e., 1, A, 2, B, etc., to 16, P). Finally, a Motor Speed condition is administered in which participants trace over a dotted line connecting circles on the page as quickly as possible, in order to gauge their motor drawing speed.

Each condition is preceded by a short practice trial. In all conditions,

participants were instructed to work as quickly and as accurately as possible. In all but the Visual Scanning condition, the examiner corrected any mistakes by placing an “X” over a wrong connection and participants were asked to continue from the last correct connection. The stopwatch remained running during such corrections. Success at the task is measured by time to completion for each condition.

The D-KEFS Trail Making Test was modelled after the traditional Trail Making Test (Reitan & Wolfson, 1985; see review of test history in Delis et al., 2001), with some important modifications in order to address some limitations of the traditional test. For example, the D-KEFS Trail Making Test contains both number

sequencing and letter sequencing conditions that are completed prior to the switching condition. In addition, the stimulus pages for the number sequencing and letter sequencing conditions contain both numbers and letters, and taken together, the two conditions match the switching conditions well in terms of the number of stimuli to visually scan and the number of lines that need drawing. The D-KEFS Trail Making Test was also created to isolate set-shifting abilities from other component skills required for the task such as visual scanning and motor speed.

Tower of Hanoi (Goel & Grafman, 1995). The Tower of Hanoi task requires the manipulation of several disks onto three rods in order to recreate a given

configuration, across three levels of increasing complexity. There are three constraints on the transformation of the start state into the goal state: (1) only one disk may be moved at a time; (2) any disk not being currently moved must remain on a peg; and (3) a larger disk may not be placed on a smaller disk.

The Tower of Hanoi task is widely used as an experimental and diagnostic tool in the neuropsychological literature to gauge planning and problem-solving abilities (Grafman et al., 1992; Shallice, 1982, 1990; Spitz, Minsky & Bessellieu, 1985). The rational underlying this interpretation seems to be that, to successfully complete the task, participants need to "look ahead" several levels and solve the problem in their heads, before physically moving any disks. If they are unable to solve the problem, it follows they were incapable of searching through the moves in their heads, and therefore they are argued to have a "planning" or "look ahead" deficit (Goel, Pullara, & Grafman, 2001).

The Tower of Hanoi task was presented on a Pentium 90 computer with a 17” monitor. Participants used a keyboard to indicate their responses.

Stroop Colour-Word Interference Task (Stroop, 1935). The Stroop task measures freedom from distractibility, selective attention, ability to resolve response conflict, and response inhibition (MacLeod, 1991; Perret, 1974). While the Stroop task is made up of three conditions, it is the interference condition which is of particular importance in this study as it measures the participant‟s ability to inhibit a dominant response (i.e., reading the word) while attending to the less salient feature of