Key ideas

• Sensation is a three-step process: receive the stimulus, transduce it into a neural signal, and transmit it to the brain for processing.
• The brain cannot use light waves, sound waves, or temperature directly, so specialized sensory receptors must convert them into neural signals.
• Each sense has its own absolute threshold, the faintest level of a stimulus you can detect at least half the time.
• The just-noticeable difference (JND) is the smallest difference between two stimuli that you can detect at least half the time.
• By Weber's law, the just noticeable difference depends on the proportion of change, so a bigger starting stimulus needs a bigger change to be noticed (an inch is big on a small kid, tiny on a tall teen).
• Our sensitivity drops when a stimulus stays constant (sensory adaptation), and one sense can shape another, as smell does for flavor (sensory interaction).
• Synesthesia is an uncommon condition in which stimulating one sense automatically and consistently produces an experience of another sense.

Key terms

transduction

The conversion of a physical stimulus into a neural signal by specialized sensory receptors.

sensation

Receiving a stimulus, transducing it into a neural signal, and transmitting it to the brain for processing.

perception

The next stage after sensation, when the brain processes the incoming sensory information.

absolute threshold

The lowest intensity of a stimulus you can detect at least 50% of the time.

just noticeable difference (JND)

The smallest difference in a stimulus you can detect half the time.

Weber's law

The principle that the just noticeable difference depends on the proportion of change, not the absolute amount of change.

sensory adaptation

Decreased sensitivity to a constant stimulus over time, such as cold pool water feeling less cold after a few minutes.

sensory interaction

When one sense influences another, such as smell affecting how food tastes.

synesthesia

An uncommon condition where stimulating one sense automatically produces an experience linked to another sense, like hearing a note and seeing a color.

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