Understanding Psychology (10th Ed)

sleep 
, the pattern is even slower and more regular, and people are least responsive 
to outside stimulation.
stage 1 sleep
The state of transition 
between wakefulness and sleep, 
characterized by relatively rapid, 
low-amplitude brain waves.
stage 2 sleep
A sleep deeper than that 
of stage 1, characterized by a slower, 
more regular wave pattern, along with 
momentary interruptions of “sleep 
spindles.”
stage 3 sleep
A sleep characterized by 
slow brain waves, with greater peaks 
and valleys in the wave pattern than in 
stage 2 sleep.
stage 4 sleep
The deepest stage of 
sleep, during which we are least 
responsive to outside stimulation.
A wake 
Stage 1 
(non-REM) 
Stage 2 
(non-REM) 
Stage 3 
(non-REM) 
Stage 4 
(non-REM) 
Sleep spindle 
REM 
Depth 
of 
sleep 
As sleep becomes 
deeper, brain waves 
take on a slower 
wave pattern
FIGURE 2
Brain-wave patterns (measured by an EEG apparatus) vary signifi cantly during the 
diff erent stages of sleep (Hobson, 1989). As sleep moves from stage 1 through stage 4, brain 
waves become slower. During REM sleep, however, the fast wave patterns are similar to 
relaxed wakefulness.
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Module 14 
Sleep and Dreams 
143
As you can see in Figure 3, stage 4 sleep is most likely to occur during the early 
part of the night. In the fi rst half of the night, sleep is dominated by stages 3 and 4. The 
second half is characterized by stages 1 and 2—as well as a fi fth stage during which 
dreams occur. 
REM Sleep: The Paradox of Sleep
Several times a night, when sleepers have cycled back to a shallower state of sleep, 
something curious happens. Their heart rate increases and becomes irregular, their 
blood pressure rises, and their breathing rate increases. Most characteristic of this 
period is the back-and-forth movement of their eyes, as if they were watching an 
action-fi lled movie. This period of sleep is called  rapid eye movement  , or  REM sleep  , 
and it contrasts with stages 1 through 4, which are collectively labeled non-REM (or 
NREM ) sleep. REM sleep occupies a little more than 20% of adults’ total sleeping time.