The clock as a focus of selective attention in those with primary insomnia: An experimental study using a modified Posner paradigm
Introduction
Primary insomnia (PI) is reportedly found in 3% of the population in western industrialised countries (Ohayon, 1996, Ohayon, 2002). According to diagnostic criteria, heightened arousal and learned sleep preventing associations form the foundations of this disorder, with patients exhibiting excessive focus upon and anxiety about sleep (American Psychiatric Association, 1994, American Sleep Disorder Association, 1997). Numerous authors contend that PI is the result of a number of psychological factors, such as maladaptive beliefs about sleep or excessive pre-sleep intrusive thoughts (Harvey, 2002, Espie, 2002, Morin, 1993).
Espie, Broomfield, MacMahon, Macphee, & Taylor (2006) propose a route into PI along the attention–intention–effort pathway which focuses on the inhibition of sleep–wake automaticity. In their conceptual paper, the authors propose that inhibition of sleep–wake automaticity can be attributed to three processes; selectively attending to sleep, explicitly intending to sleep and introducing effort into the sleep engagement process. This model has been developed by drawing on parallels in the anxiety disorder, alcohol and drug abuse literature as well as recent clinical and experimental studies on insomnia. The cognitive model of insomnia (Harvey, 2002) likewise highlights the importance of monitoring both internal and external cues in the maintenance of insomnia.
An attentional bias is said to have developed when the attention system becomes sensitive or selective to a particular theme and impacts on the individual's cognitions. Espie et al. (2006) suggest that the attentional systems of individuals with PI are particularly sensitive to sleep. Several studies have now been carried out establishing a selective attention to sleep in PI using the ICB flicker paradigm and sleep related objects (Marchetti, Biello, Broomfield, MacMahon, & Espie, 2006), using the dot probe task and sleep related words (MacMahon, Broomfield, Macphee, & Espie, 2006) and in a cancer population who have developed sleep onset difficulties (Taylor, Espie, & White, 2003).
There is widespread evidence that individuals with insomnia attribute their difficulty with sleep to excessive pre-sleep worry with PI being 10 times more likely to attribute their sleep disturbance to cognitive arousal compared to somatic arousal (Lichstein & Rosenthal, 1980). The items implicating cognition as the major cause of the sleep disturbance (e.g. ‘My mind keeps turning things over’) on the Sleep Disturbance Questionnaire are the most highly rated (Espie et al., 1989, Harvey, 2001). Therefore, we find ourselves at the juncture of having established that pre-sleep worry contributes to PI but still unable to identify a trigger for such worry.
From clinical practice it is proposed that PI selectively attend to and monitor for sleep related cues such as body sensations which are consistent or inconsistent with falling asleep and the environment for signs of not falling asleep (Harvey, 2002). One of the sleep related cues associated with the stress of not falling asleep is the bedside clock. Subjective reports highlight two types of clock monitoring in PI; how long the individual has been in bed without sleep and how many hours are left before they have to start their day (Bearpark, 1994, Harvey, 2002). Following from this, Tang, Schmidt, & Harvey (2007) investigated the association between clock monitoring, pre-sleep worry and sleep. Thirty-eight PI were instructed to either monitor a clock or a digital display unit as they were trying to get to sleep. The clock monitoring task was rated as more worry provoking and interfered with sleep more than the digital display monitoring task. The clock monitoring PI reported more pre-sleep worry and longer SOL on the experimental night compared to baseline. Hence, in the clock displaying sleep times, we have an ecologically valid stimulus which is relevant in both the perspective of the patient and clinical research but also within everyday life. Most people would be able to recall at least one occasion where sleep eluded them while being aware the time to rise was approaching.
The aim of this study was to investigate further the role of the clock in the development and maintenance of PI, by bringing together the work discussed above with selective attention in PI and the real life experimental and clinical work carried out previously which provided valuable subjective reports of the impact of the clock and time monitoring on sleep in PI.
Although the paradigms previously used to establish an attentional bias to sleep in PI are recognised as legitimate measures of attentional bias, it was felt that using a modified Posner paradigm would enable a purer measurement of engagement and disengagement to particular cues presented to the participants.
Posner has suggested that the attention system comprises measurable cognitive components (shift, engage, disengage; Posner, 1980), which are subserved by specific, neural sub-systems (Posner & Petersen, 1990) and which are open to modulation by negative emotional stimuli (Stormark, Laberg, Bjerland, Nordby, & Hugdahl 1995). In the original Posner cue-target paradigm, participants responded to a target appearing in the same (valid) or opposite (invalid) location as a previously presented cue. Results indicated faster detection of targets on cued trails, particularly at short (<200 ms) cue-target intervals. This facilitation effect was taken as evidence of the time-cost of disengaging attention from the cue to the target on invalid trials (Posner & Petersen, 1990, Posner, 1988). Over recent years, researchers have begun to apply Posner's attention model to develop a paradigm which can determine whether threatening stimuli can attract attention, i.e. modulate the engagement component of covert attention, and/or hold attention, i.e. modulate the disengage component (Broomfield, Gumley, & Espie, 2005).
Section snippets
Aims and hypotheses
The aim of this study was two-fold. First, by presenting a pictorial representation of an ecologically valid stimulus, to obtain objective evidence of the influence upon attention of monitoring the clock when set at sleep times and therefore the suggestion of the clock and sleep time as a precursor to pre-sleep worry. Second, to explore systematically, with regard to the components of the attentional system, whether participants would take longer to categorise the target on invalid trials with
Results
The experimental population was equally split between males and females with a mean age of 24 years. Table 1 shows the demographics for each sleep quality group (PI and NS) along with clinical data.
BDI and trait anxiety scores were not significantly different but PI participants had higher state anxiety (F(1,42) = 4.92, p < 0.05) which could viably reflect an increase in arousal due to presentation of a ‘negative’ cue.
Table 2 presents summary scores for self-reported sleep data. Analyses revealed a
Discussion
The purpose of this study was two-fold. First, by presenting a pictorial representation of an ecologically valid stimulus, our aim was to obtain objective evidence of the influence upon attention of monitoring the clock, when set at sleep related time, and therefore the suggestion of the clock as a precursor to pre-sleep worry. Second, we aimed to explore systematically, with regard to the components of the attentional system, whether participants would take longer to categorise the target on
Acknowledgements
This research was supported by the Carnegie Trust for the Universities of Scotland and a Glasgow University graduate scholarship.
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