TRAIT IMPULSIVITY AND OCULOMOTOR INHIBITION

Abstract

IntroductionImpulsivity is often described as a tendency to act without adequate thought. It is a personality trait which plays a vital role in behaviour and is commonly prevalent in several psychiatric disorders including; Attention- Deficit/Hyperactivity Disorder (ADHD), Borderline Personality Disorder (BPD) and substance use disorders (see Moeller Barratt, Dougherty, Schmitz, & Swann, 2001 for review). Although there has been considerable disagreement concerning the definition of impulsivity, there is growing consensus that impulsivity is multi-faceted in nature (Dickman, 1990; Patton, Stanford, & Barratt, 1995; Whiteside & Lynam, 2001). Patton et al. (1995) proposed a multi-dimensional model of impulsivity. The authors suggested that impulsivity consists of three factors; 1) attentional impulsivity (lack of focus on the task in hand), 2) motor impulsivity (a tendency to act without delay), 3) nonplanning impulsivity (lack of planning). However, in recent years impulsivity has been suggested to comprise four dimensions. Whiteside and Lynam (2001) argue that impulsivity comprises four factors; 1) negative urgency (the tendency to act rashly when experiencing negative emotions), 2) lack of premeditation (the tendency to act without deliberation), 3) lack of perseverance (the tendency to give up when activities become difficult or boring), 4) sensation seeking (the tendency to seek out activities involving an element of risk or thrill). Multi-dimensional approaches argue that an impulsive behaviour may be realised through several personality pathways.A key characteristic of impulsivity is a deficit in the suppression of prepotent motor responses - a lack of inhibitory control (Chamberlain & Sahakian, 2007). According to Nigg (2000), an important component of inhibitory control is 'executive inhibition' which is the deliberate suppression of immediate motor behaviour in the service of a longterm goal in working memory. Within this component Nigg postulates four processes; 1) interference control, 2) cognitive inhibition, 3) behavioural inhibition, 4) oculomotor inhibition. Oculomotor inhibition requires withholding a prepotent response and stopping a reflexive eye movement.A growing body of literature has explored the relationship between trait impulsivity and inhibitory control in healthy participants using various interference control paradigms e.g. Stroop task (Raz, Shapiro, Fan, & Posner, 2002), cognitive inhibition paradigms e.g. negative priming (Visser, Das-Smaal, & Kwakman, 1996), and behavioural inhibition paradigms e.g. continuous performance test (Swann, Bjork, Moeller, & Dougherty 2002), Stop signal task (Avila & Parcet, 2001; Logan, Schachar, & Tannock, 1997; Marsh, Dougherty, Mathias, Moeller, & Hicks, 2002). Comparatively little research has investigated the relationship between impulsivity and inhibitory control in healthy participants using oculomotor paradigms. Roberts, Filmore, and Milich (2011) investigated the relationship between impulsivity and manual and oculomotor inhibition in healthy adults and adults with ADHD. Oculomotor inhibition was measured using a visual stopping task and a delayed ocular response task (DORT). In the DORT, participants were asked to first focus on a white central fixation cross, after a short while, a white circle (target) briefly appeared for 100 ms to the leftor right of the fixation point. The fixation point then remained on the screen for a random interval and participants were to withhold any saccade to the target. Following this interval, the central fixation point disappeared and the display was blank for 1000 ms. Participants were told to execute a saccade to the location of the target stimulus as quickly as possible upon the disappearance of the fixation point. The authors found that specific domains of impulsivity were related to oculomotor inhibition but not manual inhibition in adults with ADHD. Moreover, there was no relationship between impulsivity and oculomotor or manual inhibition in healthy adults. …