When discussing personality, a trait is defined as a continuous variable that remains stable over time and in different situations. It can be used to predict observable behaviour relevant to that trait. One such trait is impulsivity, which has been linked to quicker response times and more errors in a forced choice reaction time task1. According to Eysenck’s 3-factor PEN model of personality, impulsivity is a trait associated with the factor of psychoticism. However, in Costa and McCrae’s Big Five model, it is classed with neuroticism.
The Barratt Impulsiveness Scale (BIS) is a 30-item self-report questionnaire used to measure impulsivity. It includes three lower-order factors: motor, attentional and non-planning impulsivity. Prisoners and people with ADHD or various addictions show a higher score than average2. This higher impulsivity may arise from poor top-down inhibitory control by the prefrontal cortex.
The possible link between self-reported impulsivity and inhibitory control can be investigated by correlating score on the BIS with results of a “go – no go” response task – a common laboratory measure of inhibitory control. Commission errors (false positive responses) indicate difficulty in inhibiting responses to distracters, and so these would be expected to correlate with score on BIS. On the other hand, omission errors (failure to respond to targets) do not involve inhibition, so the expectation is that there is no correlation with BIS score.
The target and distracter stimuli can be chosen to involve emotional processing by using positive/happy and negative/sad words. The difference in reaction times to the positive and negative words is known as the affective bias, and is generally small (although statistically significant) and positive in healthy subjects. Depressed subjects tend to respond faster to negative words than to positive words, giving a negative bias, while manic subjects show the opposite results3. No correlation is expected between affective bias and BIS score.
Over five years, 384 subjects were tested; 129 male and 255 female. All were Psychology undergraduate students aged 18-21. Subjects used the 11th version of the Barratt Impulsivity Scale questionnaire2. This is made up of 30 statements, of which the subjects were asked to rank the accuracy on a scale of 1-4 (1 being “rarely/never”, 2 being “occasionally”, 3 being “often”, and 4 being “almost always/always”). They were instructed not to hesitate for too long over individual answers, and to complete the questionnaire honestly. Of the 30 statements, 11 are related to non-planning impulsivity, 11 to motor impulsivity, and 8 to attentional impulsivity. 19 are positively loaded, and 11 are negatively loaded. This gives a total possible score of 120.
The affective “go – no go” task was executed on computers, using PsyScope. Each subject was asked to choose heads or tails in order to determine whether to start with positive or negative words as the target stimuli. This was to counterbalance any effect of starting with a particular type of word. Participants were instructed to respond as quickly and accurately as possible (by pressing the space bar) to target words, while making no response to distracter words. 10 blocks of 18 words each were presented, alternating between positive and negative blocks. In positive blocks, positive words were the target stimuli, and negative words were the distracters. The reverse was true for the negative blocks.
Subjects wore headphones, through which a loud noise was played if the subject made an incorrect response to a distracter word (commission error). No sound was played for a correct response, or for failure to respond to a target word.
The results of the gender comparison test are similar to those shown in previous BIS experiments2. The gender difference is insignificant.
As expected, there was a significant correlation between BIS total score and number of commission errors in the affective go – no go task. Motor impulsivity was the only sub-factor to correlate with commission errors. This is related to acting without thinking4, and so it may be that highly impulsive people are unable to inhibit the impulse to act and respond.
Both BIS total score and motor impulsivity correlated with omission errors, contrary to the predictions. This could be due to the distracting effect of the noise played on commission errors. However, if this were the case, attentional impulsivity would be expected to show a significant correlation, as the distraction would act to inhibit focus and concentration.
Affective bias correlated strongly with BIS total score, motor impulsivity, and non-planning impulsivity. This is not what was expected. Healthy subjects tend to show a small positive bias3. A positive bias means a slower response to positive words than to negative words. These results show that a greater impulsivity correlates with a larger positive bias, while a lower impulsivity is linked to a larger negative bias. It may be that those with a greater impulsivity find it more difficult to inhibit responses to negative words than to positive words, and so when switching between positive and negative blocks, they are faster to respond to negative words. People with a lower non-planning impulsivity may be able to plan for future blocks more readily, and so inhibition is more easily reversed. However, if this were true, we would expect no bias for those with low impulsivity, as they could switch between inhibition.
An additional factor that may have influenced go – no go task performance is that subjects were already informed that the Barratt Scale questionnaire was to investigate their impulsivity, and they had already completed it and calculated their scores. Their expectations of results may have influenced their performance on the task.