|dc.description.abstract||The main purpose ofthis study was to examine the effect ofintention on the sleep
onset process from an electrophysiological point ofview. To test this, two nap
conditions, the Multiple Sleep Latency Test (MSLT) and the Repeated Test of Sustained
Wakefulness (RTSW) were used to compare intentional and inadvertent sleep onset.
Sixteen female participants (aged 19-25) spent two non-consecutive nights in the sleep
lab; however, due to physical and technical difficulties only 8 participants produced
compete sets of data for analysis. Each night participants were given six nap
opportunities. For three ofthese naps they were instructed to fall asleep (MSLT), for the
remaining three naps they were to attempt to remain awake (RTSW). These two types of
nap opportunities represented the conditions ofintentional (MSLT) and inadvertent
(RTSW) sleep onset.
Several other sleepiness, performance, arousal and questionnaire measures were
obtained to evaluate and/or control for demand characteristics, subjective effort and
mental activity during the nap tests. The nap opportunities were scored using a new 9
stage scoring system developed by Hori et al. (1994). Power spectral analyses (FFT) were
also performed on the sleep onset data provided by the two nap conditions.
Longer sleep onset latencies (approximately 1.25 minutes) were obseIVed in the
RTSW than the MSLT. A higher incidence of structured mental activity was reported in
the RTSW and may have been reflected in higher Beta power during the RTSW. The
decent into sleep was more ragged in the RTSW as evidenced by an increased number
shifts towards higher arousal as measured using the Hori 9 stage sleep scoring method.
The sleep onset process also appears to be altered by the intention to remain awake, at
least until the point ofinitial Stage 2 sleep (i.e. the first appearance of spindle activity).
When only examining the final 4.3 minutes ofthe sleep onset process (ending with spindle
activity), there were significant interactions between the type ofnap and the time until
sleep onset for Theta, Alpha and Beta power. That is to say, the pattern of spectral power
measurements in these bands differed across time as a function ofthe type ofnap. The
effect ofintention however, was quite small (,,2 < .04) when compared to the variance
which could be accounted for by the passage oftime (,,2 == .10 to .59).
These data indicate that intention alone cannot greatly extend voluntary
wakefulness if a person is sleepy. This has serious implications for people who may be
required to perform dangerous tasks while sleepy, particularly for people who are in a
situation that does not allow them the opportunity to engage in behavioural strategies in
order to maintain their arousal.||en_US