Response inhibition is an important control mechanism in reacting effectively to sudden changes in the environment, and a deficit in this mechanism is thought to be a main feature of various impulse control disorders, including psychopathy. This study investigated the effects of reward and punishment on the inhibitory capabilities of non-clinical participants with both high and low levels of psychopathy. Forty participants performed a stop-signal task under three conditions in a mixed factorial design: a no reward or punishment (N) condition, a low magnitude reward and punishment (L) condition, and a high magnitude reward and punishment (H) condition. Participants with low psychopathy were more inhibited during both reward and punishment conditions as compared to the no reward/punishment condition. On the other hand, participants with high psychopathy showed increased response inhibition only during the L condition. The presence of reward and/or punishment, regardless of magnitude, increases response inhibition in participants with low psychopathy, whereas high levels of reward and/or punishment do not affect response inhibition in high psychopathy participants. These results suggest that a deficit in response inhibition under incentive conditions could constitute a dimensional feature or aspect of clinical and non-clinical psychopathy.
Response inhibition is the ability to inhibit planned or ongoing actions, and represents an important control mechanism for effectively reacting to sudden changes in the environment. A deficit in this inhibitory capability can induce people to behave impulsively and to react inappropriately. A strong association between response disinhibition and certain mental disorders such as substance abuse or personality disorder is well known (e.g., Miller et al., 2003 and Moeller et al., 2001). For example, Cleckley (1976) reported that a lack of self-control characterizes psychopathic behavior.
Psychopathy is defined by a constellation of affective, interpersonal, and behavioral characteristics, including egocentricity, impulsivity, irresponsibility, shallow emotions, lack of empathy, guilt, or remorse, pathological lying, manipulativeness, and “the persistent violation of social norms and expectations” (Hare, 1998, p. 188). Hare and Neumann (2008) suggested that psychopathy might be a trait that is continuously distributed within the general population. Some taxometric studies have indicated that psychopathy is indeed a dimensional construct, whether assessed by self-report (Marcus, John, & Edens, 2004) or via clinical ratings using the psychopathy checklist-revised (PCL-R; Hare, 1991 and Hare, 2003; see Edens et al., 2006 and Guay et al., 2007).
Previous research indicates that response disinhibition is characteristic of clinical psychopathy under reward and punishment conditions (Newman & Kosson, 1986). Newman and Kosson (1986) found that non-psychopathic participants showed a greater decrease in commission errors on a response inhibition Go/No-go task, in a reward and punishment situation as compared to a punishment-only condition. In contrast, clinical psychopathy did not alter behavior during the task, regardless of condition. In addition, psychopathic traits appear to be positively associated with sensitivity to reward and negatively associated with sensitivity to punishment (Ross et al., 2007). The presence of reward and/or punishment has a differential influence on response inhibition, depending on degree of psychopathy.
A previous study suggested that the presence of incentive has an influence on response inhibition in people who are prone to risk-taking (Rodrígues-Fornells, Lorenzo-Seva, & Andrés-Pueyo, 2002). Rodrígues-Fornells et al. (2002) concluded that cautious participants, who show less willingness to take risks, become increasingly cautious in the presence of reward or punishment, while risk-taking participants do not alter their behavior as a function of the presence or absence of incentives. However, no study has investigated whether response inhibition in non-clinical psychopathy is altered by the presence of reward and/or punishment. Furthermore, no study has examined the effects of reward or punishment magnitude on response inhibition. We investigated the inhibitory capabilities of non-clinical individuals with high and low levels of psychopathy using a stop-signal paradigm (SSP; Logan, 1994 and Logan and Cowan, 1984), under three reward and punishment conditions: no reward and punishment (N), low magnitude of reward and punishment (L), and high magnitude of reward and punishment (H).
The SSP provides a useful experimental measure of inhibitory abilities in both normal and clinical samples. In the SSP, participants are engaged in a reaction time task and are occasionally and unpredictably presented with a signal (e.g., a tone or light) that instructs them to inhibit their response to the stimulus. The SSP consists of both non-stop and stop trials, and in the non-stop trials, participants are required to react to certain stimuli as quickly as possible. When a stop-signal is presented, participants have to inhibit their ongoing behavior to the best of their ability. This stop-signal can occur at one of several time delays following the presentation of the stimulus. Unlike a Go/No-Go task, SSP stimuli are not divided into non-stop stimuli and stop stimuli from the very beginning. Thus, the SSP is more suitable as a measure of one’s ability to inhibit or stop ongoing reactions (Masui & Nomura, in press).
The purpose of the present study was to examine whether the presence of reward and punishment influences the response inhibition capacities of non-clinical psychopathic individuals. We conducted an SSP task in combination with the provision of rewards and punishments, and our sample included participants with low and high levels of psychopathy. Earlier findings led us to the following hypotheses regarding participants’ SSP performance: When participants are required to inhibit responses, low psychopathy participants should show increased inhibitory control under the L and H conditions as compared to the N condition. On the other hand, high psychopathy participants should not show improved response inhibition under incentive conditions.
