Sensation & Transduction

Write one example of physical information in the environment and one example of the nervous-system signal that might eventually represent it.

• Distinguish sensation from perception.
• Explain transduction as conversion of physical energy into neural signaling.
• Interpret absolute and difference thresholds as probabilistic rather than perfect cutoffs.
• Explain sensory adaptation.
• Separate direct sensory measurement from interpretation.

Related: sensory receptor · sensation · threshold · neural signal

Every sensory system begins with physical information. Vision depends on light. Hearing depends on pressure changes traveling as sound waves. Touch depends on mechanical and thermal events at the body. Taste and smell depend on chemical molecules. Vestibular and proprioceptive systems provide information about movement, balance, and body position.

Transduction converts these forms of energy into neural signals. That conversion is selective. Human eyes detect only a narrow band of electromagnetic radiation; ears detect only a limited range of sound frequencies; chemical receptors respond to some molecules and not others. Therefore, not sensing something does not mean it does not exist. It may fall outside the range of the relevant sensory system or below the detection conditions of the moment.

Thresholds are also not hard switches. A faint tone may be detected on some trials and missed on others because attention, background noise, expectation, fatigue, and random variation affect performance. Psychologists therefore define thresholds statistically—for example, the intensity detected on 50% of trials.

A difference threshold concerns noticing change. Whether a change is detectable often depends on the starting intensity. A 1-kilogram change is much more noticeable when lifting 2 kilograms than when lifting 50 kilograms. This principle illustrates that sensory systems respond to proportional as well as absolute differences.

Sensory adaptation occurs when constant stimulation produces reduced responsiveness. A smell may seem strong when entering a room and then fade from awareness. Adaptation is not the same as forgetting or choosing to ignore something. It reflects changes within sensory processing.

Sensation provides input, but perception goes further. The same retinal image can be interpreted differently depending on context; the same sound can be understood differently depending on language knowledge; the same bodily signal can be interpreted differently depending on expectations. Week 3 will build that distinction carefully.

A participant hears a very faint tone on 2 of 10 trials at one intensity, 5 of 10 at the next, and 9 of 10 at a stronger level.

1. What kind of physical signal is being discussed?
2. What sensory system could detect it?
3. What is the human detection range?
4. Could instruments detect information beyond that range?
5. What conclusion is justified?

The medium level is near a 50% detection point in this fictional dataset. Repeating the study could shift the estimate.

Using the detection table, answer four design questions.

Create a written map of at least five sensory systems. For each: physical input, receptor type/location at an introductory level, transduced neural information, one limitation, and one adaptation example. End with a paragraph explaining why sensation is not the same as perception.