Psychology / Unit 3: Sensation and Perception
3.2 Thresholds and Adaptation
Notes
- Absolute threshold: the minimum stimulus needed to detect it 50 percent of the time (such as a candle flame seen from about 30 miles on a clear, dark night).
- Difference threshold (just noticeable difference, JND): the smallest change you can detect 50 percent of the time.
- Weber's law: the JND is a constant proportion of the original stimulus. Heavier or louder stimuli need bigger changes to notice.
- Sensory adaptation: sensitivity decreases with constant stimulation, like no longer noticing a smell in a room.
- Signal detection theory says detection depends on both the stimulus and the person's alertness, expectations and motivation.
Practice
You stop noticing the sound of a refrigerator humming after a few minutes. This is:
Constant stimulation causes receptors to respond less.
According to Weber's law, which change is easiest to notice?
The JND is a proportion of the original stimulus, so small weights need smaller changes.
The minimum amount of sound needed for a person to hear it half the time is the:
That is the definition of the absolute threshold.
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