Sustained Attention Lapses and Behavioural Microsleeps During Tracking, Psychomotor Vigilance, and Dual Tasks
Degree GrantorUniversity of Canterbury
Degree NameMaster of Arts
Momentary lapses of responsiveness frequently impair vigilance and sustained goal-directed behaviour, sometimes with serious consequences. The literature underpinning research into lapses of responsiveness has generally referred to these lapses as sustained attention lapses. Currently, this literature is divided between two competing theories. On one hand, there is the mindlessness theory and, on the other, the resource depletion theory. Mindlessness theorists propose that sustained attention lapses result from the subject disengaging from sustained tasks due to their monotony and low exogenous support for attention. Conversely, the resource depletion theorists propose that sustained attention lapses arise because demands for endogenus attentional resources outstrip supply, which leads to substantially delayed response and/or errors. In the present study, the predictions from the mindlessness and resource depletion theories were investigated by contrasting performance on attention tasks that differed in cognitive workloads. In the lesser demanding task, participants performed a simple psychomotor vigilance test (PVT). In the more demanding task, the PVT was undertaken concurrently with a continuous tracking task. The higher workload imposed by the dual task should reduce task monotony and the higher attentional requirement should increase the demand for attentional resources. If the mindlessness theory is correct the dual task should result in improved vigilance and reduce sustained attention lapses. If the resource theory is correct, the added attentional demand in the dual task should decrease vigilance and increase sustained attention lapses. However, there are other types of lapses that the literature has not always clearly separated from lapses of sustained attention. One such lapse is the microsleep. Microsleeps are brief periods of non-responsiveness (0.5–15 s) associated with overt signs of drowsiness. The two theories of vigilance impairment provide contrasting explanations in the traditional vigilance literature, but neither theory addresses lapses due to microsleep events, which remains largely ignored. Microsleeps are thought to emanate from a homeostatic drive for sleep/rest and a complex interaction between the brain’s arousal and attention systems and, therefore, depend on the type of task being undertaken to modulate propensity for microsleeps. For example, a more demanding and engaging task should counteract the homeostatic drive for sleep and rest by increasing arousal. If true, tasks that increase cognitive workloads may lead to a reduction in microsleeping propensity. We aimed to test the proposal that microsleep propensity is mediated by task by including in our study a continuous tracking task, which has previously been shown to elicit microsleeps. This task may, because of its consistency and repetitiveness, be considered a boring task. Moreover, it lacks any sudden stimulus onsets and, therefore, can be considered a less engaging task than the dual-task, which features sudden onsets. If more microsleeps were found in the tracking task compared to the dual task this would provide support for the proposition that a task-generated increase in mindlessness would increase microsleep rates. Conversely, if more microsleeps occur during the dual-task, then this suggests that factors other than mindlessness influence microsleeping. Twenty-three non-sleep deprived participants – 12 females and 11 males – with an average age of 26.3 years (range 21–40 years) and an average Epworth Sleepiness Score of 5.1 (range 0–10), completed the tasks during the early afternoon. They completed the two different tasks separately and concurrently (as a dual task), with the three conditions presented in a counterbalanced order. The PVT task was an extended 30-min version of the standard 10-min PVT used in many vigilance studies to match the duration of the continuous tracking task. In this task, the participant had to respond to a discrete randomly-presented visual stimulus. As per convention, failure to respond within 500 ms constituted an attention lapse. The 30-min continuous tracking task required the participant to use a floor-mounted joystick, to monitor and track a target randomly-moving on a computer screen. In this second task, lapses show as periods of flat tracking that, when associated with overt signs of sleepiness and at least 80 % partial eye-closure, are classified as microsleeps. The dual task was the PVT and tracking tasks being undertaken concurrently. Both sustained attention lapses and microsleep rates were affected by task differences. Using only the results from participants who had at least one sustained attention lapse in either the PVT or dual task (N = 23), it was found that a participant was more likely to experience a sustained attention lapse during the more demanding dual task then the PVT task (median 15 vs. 3; range 1–74 vs. 0–76, Wilcoxon z = 3.7, p = .001). Conversely, of those participants who had at least one microsleep in either the tracking or dual task (N = 12), they were more likely to experience a microsleep during the more monotonous tracking task than the dual task (median 0 vs. 0; range 0–18 vs. 0–1, Wilcoxon z = 2.3, p = .022). Time-on-task also had an effect. Sustained attention lapses increased with time-on-task during the PVT task and dual task (χ2 5, N 23 = 48.69, p = .001; and χ2 5, N 23 = 16.33, p = .006 respectively). Moreover, sustained attention lapses increased at a greater rate during the more cognitively demanding dual task (F5, 264 = 4.02, p = .002). Microsleeps also increased with time-on-task, but only during the tracking task and not during the dual task χ2 2, N 23 = 6.72, p = .035). The pattern of results supports the resource depletion theory over the mindlessness theory. When the cognitive workload increased, sustained attention lapses were more frequent. Conversely, the results also demonstrated that when the cognitive workload was decreased, the risk of lapsing due to microsleeps increased. Clarifying this relationship between cognitive workload and two types of lapses of responsiveness, sustained attention lapses and microsleeps, is important if we are to avoid inadvertently increasing lapses of responsiveness. Both sustained attention lapses and microsleeps can have serious real-life consequences and, therefore, any contribution towards a potent, preventative strategy is important.