Modification of the startle reflex in a community sample: do one or two dimensions of psychopathy underlie emotional processing?

Abstract

Recent research on psychopathy has begun to explore two dimensions that possibly underlie psychopathy–one related more to emotional and interpersonal traits, and another related more to antisocial behaviors. A community sample of adults was assessed for psychopathy using Hare's (1991) Psychopathy Checklist-Revised (PCL-R). Eyeblinks elicited by startle probes were recorded while participants viewed pictures of emotionally-laden stimuli. Consistent with previous research, participants scoring high on PCL-R Factor 2 (“antisocial”) showed no affective modification of startle if they also scored high on PCL-R Factor 1 (“emotional detachment”). When the factor scores were analyzed together as continuous variables in a regression analysis, however, affective modification of startle was negatively related to Factor 1 but positively related to Factor 2. The results thus provide further support for a two-factor model of psychopathy.

Introduction

Psychopathy is a personality disorder distinguished by distinct emotional and interpersonal traits and deviant social behaviors. Recent empirical and conceptual work has made use of Hare's Psychopathy Checklist-Revised (PCL-R; 1991), a 20-item measure that has a two-factor solution. Factor 1 measures core personality traits associated with psychopathy, such as grandiosity, glibness, and a lack of empathy, whereas Factor 2 measures more self-defeating and antisocial behaviors, such as poor behavioral controls, juvenile delinquency, and irresponsibility. Patrick, Bradley, and Lang (1993) have labeled Factor 1 “emotional detachment” and Factor 2 “antisocial behavior.” Others have argued that the two factors appear to map onto the distinction Karpman (1941) made between primary and secondary psychopaths (McHoskey, Worzel, & Szyarto, 1998).

The PCL-R is frequently used with incarcerated samples, but rarely with non-incarcerated samples, despite the greater external validity such studies might provide (see Lilienfeld, 1994, for a review). Regardless of the kind of sample, most researchers have focused on the total PCL-R score. However, differentiating the two factors that underlie psychopathy may have implications for assessing relations between psychopathy and other personality variables (Harpur, Hare, & Hakstian, 1989). For example, Patrick (1994) administered the PCL-R as well as the trait form of the Positive and Negative Affect Schedule (PANAS; Watson, Clark, & Tellegen, 1988), and the Emotionality-Activity-Sociability (EAS) Temperament Survey (Buss & Plomin, 1984) to a sample of male prisoners. Patrick computed partial correlations between each PCL-R factor with the other variables, while holding the other PCL-R factor constant. As expected, PCL-R Factor 1 scores were negatively related to the distress and fear subscales of the EAS, and to the negative affect subscale of the PANAS. However, more surprisingly, PCL-R Factor 2 scores were positively related to these same subscales. Using different measures of affect and a two-dimension model of psychopathy, similar relationships have also been found in incarcerated adults (Harpur et al., 1989), college students (McHoskey et al., 1998), and children (Frick, Lilienfeld, Ellis, Loney, & Silverthorn, 1999).

In the present study, we examined the relationships between the two PCL-R factors and a psychophysiological measure, modification of the startle reflex. Several investigators have demonstrated that the affective modification of the startle eyeblink reflex is a useful method to study emotional processes in humans and other animals (for reviews of this literature, see Bradley et al., 1999, Davis et al., 1999). In a common paradigm with humans, participants view an affect-laden picture, such as a snake or an attractive nude model, during which there is a presentation of a loud, startling burst of white noise. The amplitudes of startle blinks that occur when the participant is viewing a negative picture are generally greater than when the picture is neutral or positive. This affective modification of startle is more likely to occur when the participant has had sufficient time to process the stimulus (i.e. greater than 1 s), although it can occur at lead intervals as short as 250 ms, depending on the task requirements (Vanman, Boehmelt, Dawson, & Schell, 1996). According to Lang and his colleagues (Lang, 1995, Land et al., 1997), this startle modification effect reflects an “affect match,” in that the startle reflex, which has a negative valence, is enhanced during a negatively valenced foreground stimulus (e.g. a picture of a burn victim), but diminished during a positively valenced one (e.g. a picture of beautiful scenery).

Patrick et al. (1993) examined the relationships of the PCL-R with startle modification with a sample of incarcerated participants. Participants viewed emotionally evocative and neutral pictures during which acoustic probes occurred between 4.5 and 6.5 s after picture onset. In one set of analyses, Patrick et al. used the total PCL-R score to form three equal groups: nonpsychopaths (low PCL-R scores), a “mixed” group (middle scores on the PCL-R), and psychopaths (high PCL-R scores). Whereas the nonpsychopaths and the mixed group both showed normal patterns of startle modification (i.e. larger blinks during the presentation of negative pictures than during the presentation of positive pictures), the startle modification to the positive and negative pictures did not differ for the psychopaths. Patrick et al. hypothesized that this abnormal pattern in psychopaths (i.e. a failure to show differences between positive and negative slides) was related more to their emotional deficits (Factor 1) than to their antisocial behaviors (Factor 2).

Therefore, in a subsequent analysis, a subsample of participants was chosen on the basis of PCL-R Factor 2 (antisocial behavior) scores as the “high” antisocial group (i.e. scores higher than 10 on Factor 2). This group was then divided into two subgroups based on their Factor 1 (emotional detachment) scores. Only those participants scoring high on Factor 2 and high on Factor 1 failed to show affective modification of startle. That is, they showed no differences in responses to positive and negative stimuli. Conversely, participants scoring high on the PCL-R Factor 2 but low on PCL-R Factor 1 displayed the normal pattern of emotional modification (smaller blinks for positive slides and larger blinks for negative slides). Patrick et al. (1993) concluded that “emotional detachment…appears to be the factor most pertinent to psychopaths’ unusual startle pattern.” (p. 323). However, it is noteworthy that, by analyzing only those participants with high Factor 2 scores, Patrick et al. did not actually examine the relation of Factor 2 to startle modification in their study.

Patrick (1994) conducted a follow-up investigation using a different sample as well as a different paradigm. On the basis of Hare's (1991) PCL-R scores, incarcerated participants comprised four groups of unequal size: nonpsychopath (low on both Factors 1 and 2), detached (high on Factor 1 but low on Factor 2), antisocial (low on Factor 1 but high on Factor 2), and psychopath (high on both Factors 1 and 2). In this study, some trials consisted of a visual cue that warned of an impending, loud, noxious noise blast. Startle probes were presented on some of these trials at long lead intervals. Although there were no group differences in baseline startle reactivity, the psychopath and detached groups showed reduced startle potentiation during the anticipation cues, compared to the nonpsychopath and antisocial groups. Patrick (1994) concluded that these results supported Patrick et al.'s (1993) conclusion that affective startle modification is specifically related to the affective and interpersonal symptoms of psychopathy. It is also important to note, however, that the antisocial group (i.e. high on Factor 2 only) evidenced a trend, although not significant due to a small sample size, of increased startle potentiation during the anticipation cues compared to the nonpsychopath group. Thus, the Patrick (1994) data suggest that PCL-R Factor 2, which seems to tap into traits associated with antisocial behavior, may also be related to affective modification of startle, but in a way that is the inverse of the Factor 1-startle modification relationship.

The present study employed an affective startle modulation paradigm with a sample consisting of volunteers from temporary employment agencies in the metropolitan community of Los Angeles. PCL-R scores for these participants were simultaneously examined with their affective startle patterns. For affective stimuli, we chose positive and negative pictures from the International Affective Picture System (IAPS; Center for the Study of Emotion and Attention [CSEA-NIMH], 1995). We did not include “neutral” pictures for the following reasons. First, it is clear that the major findings in the Patrick et al. (1993) study regarding the relationship of psychopathy to affective responses had to do with comparisons between positive and negative slides. Second, because positive and negative pictures in the IAPS are usually rated higher in arousal than are neutral pictures (Lang et al., 1997), inclusion of neutral pictures in this paradigm would have confounded the valence dimension with the arousal dimension, thus rendering conclusions involving comparisons to neutral pictures unclear. Finally, by not including a neutral slide condition, we were able to present 33% fewer trials than might have been required otherwise, thus reducing habituation to the startle stimulus.

Our design also allowed us to include startle probe trials at time intervals earlier (i.e. less than 1 s) than were used by Patrick et al. (1993). Specifically, we included 300- and 800-ms probe conditions, in addition to a 4500-ms probe condition, to explore whether factors associated with psychopathy were related to differences in timing of the affective modification of startle. For example, Vanman, Dawson, and Brennan (1998), using a slightly different picture-viewing paradigm, found that participants scoring high on a depression scale showed effects of slide valence on startle as early as 120-ms, whereas Vanman et al. (1996, Study 2) reported such modification effects at 250 ms in a “normal” sample of participants (however, the task was different from the one used in the present study). Thus, although we had no a priori predictions regarding these two early probe positions, we chose to explore this early time interval.¹

For the 4500-ms lead interval, we expected that Patrick et al.'s (1993) findings with respect to “emotional detachment” would be replicated as follows. That is, for the group with high scores on PCL-R Factors 1 and 2, no differences in startle patterns between positive and negative slides were predicted, whereas the group high in Factor 2 but low in Factor 1 was expected to show normal startle modification. In addition to conducting our analyses using groupings similar to Patrick et al.'s, we also examined the possible reciprocal suppression effects of Factors 1 and 2 that have been noted by others (e.g. McHoskey et al., 1998, Patrick, 1994).

A reciprocal suppression among two predictors occurs when one predictor is positively correlated with the criterion and the other is negatively correlated with the criterion, and the two predictors are positively correlated with one another. When reciprocal suppression occurs, both predictors may appear to have no relationship with the criterion when assessed separately in zero-order correlations (Conger, 1974). Thus, the rise in Factor 1 scores might be expected to lead to less emotional modification of startle (negative correlation between Factor 1 and modification). However, as Factor 1 rises, so does Factor 2 (positive correlation between the predictors), and Factor 2 may be positively correlated with startle modification. The decrease in modification due to an increase in Factor 1 is offset by the increase in modification due to the associated rise in Factor 2; Factor 1 and Factor 2, which would increase together, suppress and obscure each other's influence on emotional modification of startle. However, Factors 1 and 2 will have divergent relationships (i.e. one positive and the other negative) when assessed together in multiple regression (Cohen & Cohen, 1983).

Thus, we conducted regression analyses in which scores on the two PCL-R factors were treated as continuous variables. Based on Patrick et al.'s (1993) conclusions, one would expect to find that only PCL-R Factor 1 would be a significant predictor of startle modification when Factor 2 was included in the regression model. However, because this “antisocial behavior” factor is positively related to negative affect when the effects of Factor 1 psychopathy are partialed out (McHoskey et al., 1998, Patrick, 1994), and because Patrick (1994) found evidence of a trend of increased startle potentiation among those scoring high on Factor 2, we predicted that the regression analyses would reveal both a positive relationship between Factor 2 and affective startle modification, and a negative relationship between Factor 1 and affective modification.