Sensation and perception
| English | Chinese | Pinyin |
|---|---|---|
| sensation | 感觉 | gǎn jué |
| perception | 知觉 | zhī jué |
| absolute threshold | 绝对阈限 | jué duì yù xiàn |
| difference threshold | 差别阈限 | chā bié yù xiàn |
| illusion | 错觉 | cuò jué |
| perceptual constancy | 知觉恒常性 | zhī jué héng cháng xìng |
The eye senses light; the brain perceives a face
- Sensation 感觉 is the detection of a stimulus by a sense organ.
- Perception 知觉 is the brain's interpretation of what was detected.
- This distinction is the most examined thing in the unit, and using the words interchangeably is the most common way to lose the mark.
The eye detects wavelengths of light. What is that?
Detection by a sense organ is sensation. Seeing red is the brain's interpretation, which is perception.
Thresholds
- The absolute threshold 绝对阈限 is the smallest stimulus you can detect at all.
- The difference threshold 差别阈限 is the smallest change you can notice.
- The difference threshold is proportional, not fixed: adding one candle to a room with two is obvious, and to a room with fifty is not.
Adding one candle is noticeable in a room with two but not with fifty. What does this show?
The noticeable change scales with the amount already present.
Constancy and illusion
- Perceptual constancy 知觉恒常性 keeps an object looking the same size, shape and colour as viewing conditions change.
- A door swinging open projects a changing shape onto your eye, and you see one rectangular door throughout.
- An illusion 错觉 works by exploiting a rule the brain applies correctly almost always — which is why illusions are evidence about perception rather than failures of it.
A door swinging open projects a changing shape on the eye, yet you see one rectangular door.
That is perceptual constancy: the brain holds the object steady while the input changes.
Why an illusion is not a mistake.
The brain assumes a scene is lit from above, because for our whole history it was. That assumption is right so consistently that it is worth building in.
An image lit from below makes bumps look like dents. The brain is not malfunctioning; it is applying a rule that pays almost every time to the rare case where it does not.
Illusions are evidence about the rules, and saying which rule is being exploited is what a good answer does.
Why do illusions count as evidence about perception rather than as failures of it?
The rule pays almost every time. An illusion is the rare case it does not, which is what makes it informative.
Perception is construction, not reception. The brain builds a stable world from changing, incomplete and ambiguous input — and the gaps it fills are invisible to us precisely because it fills them.
In one sentence, explain the difference between sensation and perception using an example.
Example: "The ear senses air vibrations, but perceiving them as a familiar song is the brain's interpretation."
Do not write "sensation" when you mean "perception". The eye senses wavelengths; the person perceives red. A question that offers both words in the options is testing exactly this, and it is the unit's most reliable examinable point.