Page 199 - Understanding Psychology

Figure 7.2 Patterns of Sleep
Awake Participant Wakens
One REM Sleep
Two
Three
Four
Stages of Sleep
Awake One
Two Three
Four
REM sleep
1 sec
Early Stages
In Stage I sleep, your pulse slows a bit more and your muscles relax, but your breathing becomes uneven and your brain waves grow irregular. If you were awakened dur- ing this stage, you would report that you were “just drifting.” This phase lasts for up to 10 minutes and is marked by the presence of theta waves, which are lower in amplitude and frequency than alpha waves. At this point, your brain waves occasionally shift from low-amplitude, high- frequency waves to high- amplitude, low-frequency waves—a pattern that indicates you have entered Stage II sleep. Your eyes roll slowly from side to side. Some 30 minutes later, you drift down into a deeper level of Stage III sleep, and large-amplitude delta waves begin to sweep your brain every second or so.
Later Stages
The top diagram shows the passage of a sleeper through the various stages of sleep over a seven-hour period. The bottom diagram shows the patterns of electrical activity (EEGs) in the brain that correspond to the various stages of sleep. The EEG pattern shown for being awake is one that occurs when a person is resting quietly with eyes closed. How often during a night’s sleep does a person reach Stage IV?
Stages of Sleep
11 pm
12 am
1 am
2 am
Hour of the Night
4 am
5 am
6 am
3 am
Stage IV is the deepest sleep of all, and it is difficult to waken a sleeper in this stage. Large, regular delta waves occurring more than 50 percent of the time indicate you are in a state of deep sleep. If you are awakened by a loud noise or sudden movement, you may feel dis- oriented. Talking out loud, sleepwalking, and bed-wetting—all of which may occur in this stage—leave no trace on the memory. Deep sleep is important to your physical and psychological well-being. Perhaps this is why people who are able to sleep only a few hours at a time descend rapidly into Stage IV and remain there for most of their nap.
On average a person spends 75 percent of sleep time in Stages I through IV. Once in Stage IV, something curious happens. While your muscles are even more relaxed than before, your eyes begin to move
Chapter 7 / Altered States of Consciousness
185