A primary motivation of using factor analysis in this study was to characterize the multidimensional aspect of impulsivity. As hypothesized, the PCA yielded a multi-factorial solution, identifying five factors that together predicted nearly 70% of the total variance, with a good inter-consistency among factors. Even though preliminary, the results of our supplementary factor analyses ensured that that each subsample separately yielded a similar factor structure to that found in the overall sample. In general, the ordering of factors across subsamples was slightly different. The only noteworthy difference in factor structure was that Factor 4 was somewhat mutable, exchanging some scales (Zuckerman versus BIS/BAS Behavioral Inhibition) with Factors 1 and 2 depending on which specific subsample is examined. Overall, the factor analysis findings suggest different relationships between behavioral discounting of rewards and self-reported measures in different groups. Self-reported behavioral inhibition is more closely linked with behavioral discounting of rewards in control subjects and sensation-seeking with behavioral discounting of rewards in the ARA group. These findings are intriguing and suggestive of a between-group difference in self-perception measures as they relate to behavioral measures of discounting of monetary rewards. However, we caution against over-interpreting these findings, as the similarities among factor structures greatly outweigh the differences, and the relatively small sizes of the subgroups raise questions about the stability of any observed differences.
There have been numerous previous attempts to clarify the factorial nature of impulsivity (Caseras 2003
; Miller et al 2004
; Quilty 2004
; Reynolds, et al. 2006
; Whiteside and Lynam 2003
). Although a valid criticism of this literature is that different results are obtained depending on which tests are selected to examine, a surprising degree of convergence has emerged on certain key theoretical issues. For example, one central theoretical prediction that continues to be validated across studies derived from Gray's influential theory of personality (Carver and White 1994
), is the finding that scales measuring inhibitory influences on behavior (e.g., Gray's BIS from the BIS/BAS) remain empirically distinct from scales that measure activation, reward, approach, or similar conceptualizations, which are related to different definitions of impulsivity. Our data found the BAS subscales of the BIS/BAS loaded together onto factor 1, which we labeled “Self-Reported Behavioral Activation.” In contrast, the BIS subscale from the BIS/BAS joined scores from the Reynolds EDT measuring delay discounting on factor 4. Although in some studies, tasks theoretically consistent with BAS function are found to be less homogenous in factor structure than BIS indicators (Caseras 2003
), several studies have found that BAS subscales from the BIS/BAS often load together (Miller et al 2004
; Quilty 2004
). Miller and colleagues reported that all three BAS factors loaded onto a single factor, although in that analysis dual-factor loadings were permitted and certain BAS indicators were also linked to other impulsivity factors. Similarly, Quilty performed a confirmatory factor analysis to show that numerous measures thought to measure the Behavioral Activation System did indeed correlate highly with a latent BAS factor. Interestingly, in that study scores which are often conceptualized as ‘impulsive’ such as the Zuckerman SSS and the BIS-11 were found to better represent a separate factor. This is exactly the same as found in our analysis, where all three BIS-11 subscores loaded onto their own factor with the SSS summary score, which we termed “Self-Reported Impulsivity.” These findings reinforce the validity of a primary distinction between inhibition versus activation/reward influences on behavioral tendencies, and extend this understanding to group with varying levels of involvement with substance disorder.
Another area of convergence highlighted by our findings is the separation of reward-based conceptualizations of impulsivity versus those that denote failures in response inhibition/prevention, inability to resist urges, or failure to think through the consequences of actions. This study found that the SPSRQ Sensitivity to Punishment and Sensitivity to Reward indices loaded onto a separate category compared to either domain of the BIS/BAS. This is noteworthy because the SPSRQ was developed in the context of Gray's BIS/BAS theory (Torrubia, et al. 2001
), but instead seems to capture a unique dimension of personality. In our study, both measurements of SPSRQ that reflect desire for reward or fear of punishment were related to scores on the Padua scale of compulsivity. One possible interpretation is that this reflects a tendency towards behavior that is strongly influenced by external influences, regardless of source. If accurate, this might account for the dissociation of this scale from more conventional indices of either the behavioral activation or inhibition systems postulated by Gray, or reconceptualized by Corr as the Reinforcement Sensitivity Theory (Corr 2004
), in which the BIS is proposed to specifically mediate conflict between the BIS/BAS. Dysfunction of neural systems thought to underlie conflict resolution have become increasingly of interest to neuroimaging researchers of substance disorder (Franken, et al. 2006
; Goldstein and Volkow 2002
; Jentsch and Taylor 1999
; Kaufman, et al. 2003
). Such research may soon help us better understand relationships among this impulsivity factor found here, theories of impulsivity, and neurobiological dysfunction.
Another important dimension of our results involves the relationship between self-report and laboratory-based measurements of impulsivity. We initially predicted that our results would be in line with other well-conducted studies that found no relationships between self-report and laboratory measures (e.g., Reynolds et al 2006
). However, our results were not entirely consistent with this hypothesis. The BART measure did emerge as a single factor and was orthogonal to all other measures. In contrast, our other computer based task – the EDT – loaded onto a factor with the BIS scale. This is contrary to the report of Reynolds et al. (2006)
, in which the EDT and BART grouped under a single factor dimension that they named “impulsive decision making.” One possible reason for the difference might be that the Reynolds study used a sample on average 10 years younger than ours. As such, it could have been more prone to “methodology effects,” perhaps in part due to maturational differences on tasks conceptually similar to these instruments. Another possibility is the utilization of a different set of behavioral and computer based tasks in the study to measure impulsivity.
The primary value in these findings is to extend an emerging conceptualization of the relationship among indicators of impulsivity to samples defined by their involvement with substance misuse. We took care to utilize instruments commonly employed in the substance disorder field in the hopes that the current results can aid in the interpretation of future research about either the risk or consequences of substance disorder relative to impulsivity. This point is not trivial, as numerous factors are known to bear on the risk for onset of substance abuse (e.g., exposure to drug, age at first use, peer/social influences, plus major “protective” factors such as stable family structure, engagement in extracurricular activities). Analogously, many studies show the deleterious effects of addiction on brain structure and optimal function (Magalhaes 2005
; Spampinato, et al. 2005
). Therefore, it is notable that a coherent multidimensional factor structure, largely in agreement with previous studies, emerges in a sample chosen for its heterogeneity. On the one hand, this supports the conceptualization of impulsivity as both a determinant of, and consequence of substance disorder. On the other hand, the results have important implications for future study of the relationship between substance disorder and different aspects of impulsivity. Several recent studies have supported the idea that impulsive behavior is related to substance abuse (Bickel et al. 1999
; Fillmore and Rush 2002
; Lejuez et al. 2003
; Madden et al. 1997
; Reynolds et al. 2004
) .However, there is no clear consensus between these studies on the role of impulsivity in substance abuse. We also found that even though multiple raw behavioral variables initially served to differentiate the groups, the factor structure between the two groups remained almost the same with minor changes that were consistent with our initial hypothesis. Congruent with previous studies that showed variables such as Zuckerman sensation seeking, SPSRQ and BIS-11 to predict successfully higher impulsivity or other related physiological behaviors in at-risk/addicted groups (Brunelle, et al. 2004
; Moeller, et al. 2002
; Petry 2001
), reports that the factor constructs “Self-Reported Compulsivity and Reward/Punishment Sensitivity” (SPSRQ, Padua) and “Self-Reported Impulsivity” (BIS-11, Zuckerman sensation seeking) successfully discriminated our two study groups. As expected, the ARA groups score higher on each of the factor scores with respect to their controls counterpart. A dual-factor conceptualization of impulsivity has been proposed numerous times and supported by increasing amounts of evidence (Caseras 2003
; Dawe and Loxton 2004
; Patton, et al. 1995
; Reynolds 2006
; Reynolds et al 2006
; Whiteside and Lynam 2003
). Our multidimensional results are largely consistent with previous studies that show drug abusers or subjects genetically at-risk of addiction score higher than non-users on self-report measures of impulsivity, sensation seeking and inattention (Conrod, et al. 1997
; de Wit and Richards 2004
; Slater 2003
; Zuckerman, et al. 1990
). This study therefore utilizes a useful data-analytic technique to take an important step forward in relating the role of specific impulsivity related self-report and behavioral measurements that might be sensitive to substance abuse variables.
Even though we included several behavioral measures, future research could add other types of impulsivity assessments (especially more laboratory/computer-based tasks such as Go/No-Go, Stop Task etc.: Newman, et al. 1985
; Reynolds, et al. 2008
) to capture all relevant domains. Several potential caveats are noted. First, there was a relatively unfavorable case-to-variable ratio in the within-group sample that limited our ability to analyze further sub-groups of interest in the ARA sample (i.e. examining alcoholic and recovering alcoholics or former versus current drug users, etc.). Second, because the temptation exists with factor analysis to ‘invent’ personality dimensions based on the arbitrary results of the approach, we tried to be judicious in naming the factors that emerged from our analysis. Rather than add to a debate on the exact composition of each dimension, we instead chose to discuss how our general findings coincide with emerging theoretically-meaningful findings from the pool of similar studies that have been conducted in the past several years. We believe this is by far the most useful point to make about this type of study. We also note that the inclusion of “Self-Reported” or “Behavioral” terminology in factor naming reflects the still incompletely understood relationships between these two types of methodological approaches to measuring impulsivity. Indeed, a question often raised in characterizing impulsivity is whether it reflects traits that are fairly stable over time, or are transient and sensitive to environmental influences. Self-report measures of impulsivity are often purported to measure the former while the latter is captured more by laboratory tasks. However, even this distinction has been brought into question with studies that find self-rating of impulsive personality traits vary depending on severity of acute psychopathology or similar contextual factors (e.g., Corruble, et al. 2003
; Corruble, et al. 1999
). However, it is encouraging that separate instruments did consistently load onto their own factors. Indeed, only the BART task was left isolated from other measures. This reinforces the multidimensional nature of impulsivity and how impulsivity in relation to substance disorder risk/consequence shares aspects among several commonly-used indicators. We were not able to fully analyze separate subgroups. However, several theorists have proposed that impulsivity is a shared liability to all forms of substance disorder (Lane, et al. 2003
; Logue, et al. 1992
; Paine, et al. 2003
; Richards, et al. 1999
), so we feel our results are meaningful. Finally, we recognize our choice of Varimax rotation imposes constraints on the solution, an alternative factor analytic approaches could find somewhat different results.
In summary, we provide a useful extension to previous studies and further reveal the multidimensional construct of impulsivity measures, with meaningful associations between various self-report and laboratory measures in a cohort of healthy controls and ARA subjects. In addition, we also demonstrate the differences in the underlying constructs of impulsivity between the two groups. We believe that this would allow researchers to investigate the physiological systems underlying the behaviors and in turn help in developing targeted treatments for impulsivity related pathological behaviors.