Pupillary Light Reflex and Rate of Intensity Change

Steps:

• Examine the graph of pupil diameter versus time to identify periods A, B, C, D.
• Note that pupil diameter decreases as light intensity increases due to constriction.
• Calculate the rate of change (slope) of pupil diameter in each period; steeper negative slope means faster intensity increase.
• Select the period with the steepest negative slope.

Why D is correct:

• Period D shows the steepest decrease in pupil diameter, indicating the fastest light intensity increase via the pupillary light reflex law.

Why the others are wrong:

• A: Shallow slope shows slow intensity increase.
• B: Moderate slope indicates intermediate rate.
• C: Flat or slight change means minimal intensity increase.

Final answer: D