Impulsive Behaviour in Specific Populations

In addition to research on impulsive choice in samples from the general population and in animals, specific populations have been studied. Impulsivity is identified as a component of many clinical diagnoses (such as ADHD) and undesirable behaviours such as substance abuse and gambling. Critchfield and Kollins (2001) noted the necessity for research on discounting in individuals who present impulsive responding in order to increase understanding of "socially important behaviors" (p. 101). For example, research has been conducted on behaviours such as drug addiction (Bickel & Marsch, 2001; Coffey, Gudleski, Saladin & Brady, 2003), smoking (Johnson, Bickel & Baker, 2007; Reynolds, Karraker, Horn & Richards, 2003), alcoholism, gambling (Vitaro, Arseneault & Tremblay, 1997), and on individuals with psychiatric

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disorders (Crean, De Wit & Richards, 2000), such as schizophrenia, and pathologies such as OCD (Obsessive Compulsive Disorder).

Estle et al. (2007) reported that consumable rewards (such as sweets) had similar properties to abused substances (e.g., beer). Estle et al. indicated that further research regarding discounting in substance abusers and the characteristics of such consumable rewards was important for future intervention strategies. For example, research conducted by Yi, Gatchalian and Bickel (2006) claimed that examining discounting of past outcomes in substance abusers could provide useful insight regarding intervention.

In a review, Bickel and Marsch (2001) compared research on impulsivity in substance abuse, including smoking and alcohol. They reported that findings from Vuchinich and Simpson (1998) indicated that higher rates of discounting were produced by participants who drank heavily than participants who drank occasionally. Additionally they presented evidence to suggest that individuals who were drug dependent presented highly impulsive responding on delay discounting measures. They maintained that to enable increased understanding of characteristics of rewards and impulsiveness, future research should use delay discounting measures to assess impulsiveness in a variety of populations.

Richards et al. (1999) used the Double-Limit algorithm to determine the effect of small amounts of alcohol on discounting and presented participants with a number of self-report scales (including the Eysenck Personality Inventory: Eysenck & Eysenck, 1968) and the Impulsiveness-Venturesomeness-Empathy questionnaire (IVE: Eysenck & Eysenck, 1978). Although they reported that the

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self-report scales and behavioural discounting measure correlated slightly, discounting was not affected by alcohol intake. They reported that similar results had been gained previously, but claimed that the amount of alcohol given to the participants in their study may not have been sufficient to generate an effect. This illustrates the difficulties in studying impulsiveness in substance abuse due to ethical and practical constraints.

Nonetheless, increasingly research has been conducted on discounting in drug abusers in an attempt to further knowledge about characteristics of such behaviour and subsequently improve intervention strategies. Kirby, Petry and Bickel (1999) compared scores on a monetary choice questionnaire (developed by Kirby & Maraković, 1996) with discounting rates and self-report measures of impulsivity (the BIS-11 and Eysenck's I.5 questionnaire). The self-report scales and discounting measure correlated positively and discounting by heroin addicts was found to be higher than discounting by non-drug taking controls. Kirby et al. emphasised the immediacy of the rewarding “pleasant feelings, euphoria, and relief from withdrawal or dysphoria” (p. 78) in drug use, compared to the delayed negative experiences, such as withdrawal, that occur in making a more self-controlled choice of not taking drugs. Similarly, Madden, Bickel and Jacobs (1999) studied delay discounting (using cards with amounts and delays from Rachlin et al., 1991) in heroin-dependent participants. In support of previous research (e.g., Madden et al., 1997), they found that heroin-dependent individuals discounted heroin rewards at higher rates than monetary rewards, thus emphasising the high immediate value of heroin perceived by heroin- dependent individuals.

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Coffey, Gudleski, Saladin and Brady (2003) reported that cocaine-dependent participants presented higher impulsiveness scores in the self-report scales (the I.7 Impulsiveness Questionnaire and the BIS-11) and higher discounting rates of hypothetical monetary rewards than matched controls. Furthermore, monetary rewards were discounted at slower rates than hypothetical cocaine rewards by cocaine-dependent participants, further emphasising the value of obtaining immediate cocaine in cocaine-dependent individuals. They reported that the delays used had been successfully discounted in previous drug research, though Coffey et al. found the cocaine-dependent participants were intolerant of the 1 week delay: participants preferred the "$1 of crack/cocaine immediately rather than wait 1 week for $1000 worth of crack/cocaine" (p. 22). Similar to Madden et al. (1999), Coffey et al. suggested that the intolerance could indicate the high immediate reward value of crack/cocaine compared to other drugs, and that further comparison research was needed to increase knowledge in this area.

Impulsivity has also been studied in relation to smoking behaviour. Mitchell (1999) found smokers responded more impulsively on discounting choice tasks, had higher impulsive scores on personality scales and shorter response times than non-smokers. Higher levels of risk-taking and impulsivity were found in scores from personality scales for male adolescent smokers than non-smokers (Williams, 1973). Additionally, Barman, Pulkkinen, Kaprio and Rose (2004) found evidence of an increased likelihood of cigarette experimentation in individuals who reported high impulsivity.

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In a further study of impulsivity in smokers, Epstein, Richards, Saad, Paluch, Roemmich and Lerman (2003) administered two delay discounting measures, including Kirby, Petry and Bickel’s (1999) monetary-choice questionnaire and the Double-Limit algorithm. Epstein et al. reported that both measures strongly reflected higher impulsive choice in smokers than non-smokers. The Double- Limit algorithm was also used by Johnson, Bickel and Baker (2007) with "never smokers", "light smokers" and "heavy smokers". They reported evidence in support of previous research suggesting higher discounting rates in smokers compared to individuals who have never smoked, and consequently highlighted the validity and reliability of such measures. More specifically, heavy and light smokers discounted money more than never smokers, and cigarettes more than money and health, demonstrating the high immediate value of cigarettes to smokers (similar to the high immediate value of drugs to drug-dependent individuals).

A study by Sturm, Furnell and Gillberg (2004) reported that of 101 children with Autism Spectrum Disorders (ASD) who participated in their research, 50 percent presented impulsiveness. Research has also been conducted on impulsiveness in individuals diagnosed with ADHD (e.g., Winstanley, Eagle & Robbins, 2006; Solanto et al., 2001). Neef and colleagues conducted a series of studies with individuals with special educational needs (Neef et al., 1992), emotional difficulties (Neef et al., 1993), learning and behavioural difficulties (Neef et al., 1994), and studies comparing children with ADHD (medicated and non-medicated) to typically developing controls (Neef, Bicard & Endo, 2001; Neef et al., 2005).

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Moeller et al. (2001) reviewed research that suggested impulsive traits were commonly presented by individuals with ADHD and Conduct Disorder, Substance abuse, Borderline Personality Disorder, Bipolar Disorder, and Antisocial Personality Disorder. It was highlighted that impulsivity was an element included in the DSM-IV diagnostic criteria for some of these disorders. Crean, De Wit and Richards (2000) used Richards et al.'s (1999) Double-Limit algorithm to measure discounting in 24 patients with disorders such as those mentioned above. They characterised participants on the likelihood of their engaging in impulsive behaviour according to the DSM-IV criteria: 12 were described as “low risk” and 12 as “high risk”. Participants also received the IVE (I.7) questionnaire (Eysenck, Pearson, Easting & Allsopp, 1985). Crean et al. reported that the high risk patients discounted at a higher rate than the low risk patients, and scored higher on the self-report scale.

Neef et al. (2005) studied impulsive choice in children with ADHD (medicated and non-medicated) and non-ADHD controls. Both medicated ADHD children and non-medicated ADHD children were reported to be mostly influenced by reward immediacy, rather than quality of the reward or task effort, indicating no effect of medication on impulse control. The non-ADHD participants were most influenced by reward quality, and thus were reported to have presented more self-controlled responding. Additionally, this study highlighted individual differences in reward quality which could be used against immediacy of reinforcement to promote self-control (in support of research by Neef et al., 2001).

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As described previously in this review, there is evidence to suggest that impulsivity is involved in undesirable behaviours such as addictions to cigarettes, drugs, or gambling. Impulsivity is also referred to in several clinical diagnoses, including ADHD and bipolar disorders. Research on impulsivity within specific populations could generate a better understanding of the difficulties such individuals encounter, and in turn assist in the development of strategies to decrease undesirable behaviour and increase desirable behaviour possibly through self-control training.