AP Psychology · Lesson 3

Sleep and sensation

Know Know it

A circadian rhythm is the body's cycle of about 24 hours. Light signals reach the suprachiasmatic nucleus in the hypothalamus, which tells the pineal gland when to release melatonin. Darkness raises melatonin and makes us sleepy.

Sleep moves through NREM stages 1 to 3 and then REM sleep, in cycles of about 90 minutes. Stage 2 shows sleep spindles. Stage 3 shows slow delta waves and is the deepest sleep. REM brings vivid dreams, fast brain waves and near paralysis of the large muscles. REM periods get longer as the night goes on.

Sleep helps consolidate new memories. Common sleep disorders include insomnia (trouble falling or staying asleep), sleep apnea (breathing stops again and again), narcolepsy (sudden attacks of sleep) and sleepwalking, which happens in NREM stage 3.

Sensation begins with transduction: receptors turn energy such as light or sound into neural signals. The absolute threshold is the faintest stimulus detected half the time. The difference threshold is the smallest change we notice, and Weber's law says it is a constant proportion of the original stimulus. Sensory adaptation is the drop in response to an unchanging stimulus.

In the eye, rods work in dim light and cones detect color and fine detail. Trichromatic theory explains color at the cones, and opponent-process theory explains afterimages. In the ear, hair cells in the cochlea do the transduction. Place theory explains high pitches, and frequency theory explains low ones.

Trap REM is not the deepest sleep

Deep sleep means NREM stage 3, with slow delta waves, when a person is hardest to wake. In REM the brain is highly active, almost as if awake, while the large muscles are mostly still.

Worked example Easy

After a few minutes in a room, you no longer notice the hum of the refrigerator. What explains this?

  1. Transduction
  2. Sensory adaptationAnswer
  3. Absolute threshold
  4. Opponent processing

How to solve it

  1. The sound did not change, but your response to it did.
  2. A fading response to a constant stimulus is sensory adaptation.

Why each choice is right or wrong

  • A. Incorrect. Transduction is turning sound into neural signals, and it does not explain why the hum fades from notice.
  • B. Correct. Receptors respond less to an unchanging stimulus over time, which is sensory adaptation.
  • C. Incorrect. The hum is well above the absolute threshold, since you heard it at first.
  • D. Incorrect. Opponent processing explains color vision and afterimages, not a fading sound.

Explain Explain it

Task verbs: explain, predict

When you explain a sleep finding, name the stage or process, then connect it to a change in behavior such as memory, mood or alertness.

Worked example Medium

A sleep lab records slow, large delta waves, and the sleeper is very hard to wake. Which stage is this most likely?

  1. NREM stage 1
  2. NREM stage 2
  3. NREM stage 3Answer
  4. REM sleep

How to solve it

  1. Delta waves are the slowest brain waves.
  2. They dominate the deepest NREM stage, which is stage 3.

Why each choice is right or wrong

  • A. Incorrect. NREM stage 1 is light sleep with slowing waves, and the sleeper wakes easily.
  • B. Incorrect. NREM stage 2 is marked by sleep spindles, not mostly by delta waves.
  • C. Correct. Delta waves and difficulty waking mark NREM stage 3, the deepest stage of sleep.
  • D. Incorrect. REM sleep shows fast, wake-like brain waves, not slow delta waves.

Predict Your turn

A student studies a list of terms and then stays awake all night. Predict how this affects what she remembers a few days later, and explain why.

Write it, then compare. Nothing you type here is saved or graded.

Compare with a model answer

A full answer does this

  • Predicts that the student will remember less of the material
  • Explains that sleep helps consolidate new memories

Model answer

She will probably remember less of the terms than she would after a full night of sleep. During sleep, especially deep NREM sleep and REM sleep, the brain consolidates new memories by strengthening and storing them. Staying awake cuts that process short, so more of the material is lost.

Apply Apply it

Practice these topics. AP Practice questions on exactly what this lesson covers, with an explanation for every answer.