Driver Drowsiness Detection and Measurement Methods - Driver Drowsiness Detection: Systems and Solutions - page 7

Table 2.1 Typical administration of MSLT test

Step Time Subject's Chores

1 5AM Lights on

2 7AM Subject awake

3 7:30 AM Measuring brain activity

4 8AM 20 min nap

5 9AM Subject awake—measuring brain activity

6 10 AM 20 min nap

7 12:30 PM Subject eats lunch—measuring brain activity

8 1PM 20 min nap

9 3:30 PM Subject leaves

fall asleep on a scale from 0 (no chance) to 3 (high chance). Subjects can score
between 0 and 24 points. Subjects scoring less than 10 are considered awake or
slightly sleepy, while 15 points or more indicate severe sleepiness.

￿ Multiple Sleep Latency Test (MSLT) [ 7 ]: a test based on the presumption that

people who fall asleep faster are more sleep deprived. The MSLT measures the
tendency to fall asleep in a standardized sleep-promoting situation during four
or five 20-min nap opportunities that are spaced 2 h apart throughout the day
and in which the individual is instructed to try to fall asleep (Table 2.1 ). Since
brain wave sleep-staging criteria are very well established, the intervals of time
it takes the subjects to fall asleep can be easily measured. If a subject needs less
than 5 min to fall asleep, he or she is considered pathologically sleepy; whereas
taking more then 10 min is considered normal.

￿ Maintenance of Wakefulness Test (MWT) [ 45 ]: a test in which individuals are

instructed to try and remain awake. Their attempt is monitored over a period of
20 min. If a subject can stay awake over that period of time, he is considered
awake and capable of operating a vehicle. But if a subject falls asleep within the
first 15 min, he can be considered too sleep deprived to drive.

￿ Stanford Sleepiness Scale (SSS) [ 21 ]: an instrument that contains seven state-

ments through which people rate their current level of alertness (e.g., 1=
“feeling ”). The scale correlates with

standard performance measures, is sensitive to sleep loss and can be administered
repeatedly throughout a 24-h period. Typically, subjects are asked to rate their
alertness level every 2 h throughout the day by choosing a single number
associated with specific alertness description (Table 2.2 ).

::: wide awake” to 7= “ ::: sleep onset soon :::

￿ The Karolinska Sleepiness Scale (KSS) [ 2 ]: contains questions that guide

subjects to provide, to the best of their ability, a self-report of the quality of their
sleep. Laboratory tests and field studies suggest that the measurements gathered
by this method seem to adequately cover and relate to various sleep and lack of
sleep scenarios. This is the most commonly used drowsiness scale—a nine-point
scale that has verbal anchors for each step (Table 2.3 ).