Distinguish corrective feedback from reinforcing change
Use both sides of a supplied reference level to evaluate a response.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall hormone production and blood transport, respiration, liver storage and electrical impulses along neurones.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which quantity helps judge a corrective response?
What you will learn
- Test whether a response reduces the departure
- Avoid an always-decrease interpretation
Distinguish corrective feedback from reinforcing change
| Feature | Meaning |
|---|---|
| 7→6 around 5 | Departure magnitude 2→1: corrective |
| 3→4 around 5 | Departure magnitude 2→1: corrective |
| 7→8 or 3→2 | Departure magnitude 2→3: reinforcing |
| Partial correction | Closer to the reference does not mean already equal |
Test whether a response reduces the departure
To classify a response as negative feedback, compare the variable before and after the response with its supplied set point. The relevant measure is the magnitude of the departure. A response moving a high value lower towards the reference is corrective, and a response moving a low value higher towards the reference is also corrective.
With a reference of 5 model units, 7→6 changes the departure magnitude from 2 to 1, while 3→4 also changes it from 2 to 1. Both reduce the difference from the set point. In contrast, 7→8 or 3→2 increases the departure magnitude from 2 to 3; those specified changes reinforce the departure rather than correcting it.
Avoid an always-decrease interpretation
The response may still be incomplete. A final value of 6 is closer to 5 but has not yet returned to the reference. Distinguish moving towards the set point from already reaching it. Time delays and continued disturbance can affect the observed path, so the supplied short record is evidence for its stated interval rather than an entire physiological history.
Apply this reasoning to a new internal variable by naming its reference and direction of departure. Do not call a response negative feedback merely because a hormone concentration falls or because its name sounds inhibitory. Judge whether the regulated condition moves towards its set point, and explain how corrective activity is reduced when the departure becomes smaller.
Sources for this lesson
Pause and explain
Which change is corrective around set point 5?
Worked example
Classify 7→6 and 3→2 around set point 5.
Show the worked solution
- 7→6 reduces departure from 2 to 1.
- 3→2 increases departure from 2 to 3.
Answer 7→6 is corrective; 3→2 reinforces departure.
Try a topic test
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Classify 7→6 and 3→4 around reference 5 using departure magnitudes.
Give me a hint
Find the distance from 5 before and after.
Compare my reasoning
- Both start two units away.
- Both finish one unit away.
Both are corrective changes: departure magnitude falls from 2 to 1 model unit.
Look for these in your work
- Calculate both departures
- Identify corrective direction
Classify 7→8 and 3→2 around reference 5.
Give me a hint
Compare magnitudes rather than signs alone.
Compare my reasoning
- Both start two units away.
- Both finish three units away.
Both reinforce the departure: its magnitude rises from 2 to 3 model units.
Look for these in your work
- Compare both distances
- Identify reinforcing change
An answer calls 7→6 a complete return to set point 5. Improve it.
Give me a hint
Closer does not mean already equal.
Compare my reasoning
- The difference is reduced from two units to one.
- The final value remains above the set point.
The response moves towards the set point and reduces the departure, but the value 6 remains one unit above reference 5.
Look for these in your work
- Recognise partial correction
- State the remaining difference
Common mistakes
- Using the sign of a change alone to classify feedback.
- Calling a value nearer the set point already identical to it.
What can you explain now?
Which change is corrective around set point 5?
Compare with the explanation
3→4
It moves a low value towards the reference.
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Make it stick
Evaluate supplied changes by their distance from a set point.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.