Chapter 1, Problem 9P

The human eye has a biological control system that varies the pupil diameter to mamtain constant light intensity to the retina. As the light intensity increases, the optical nerve sends a signal to the brain, which commands internal eye muscles to decrease the pupil's eye diameter. When the light intensity decreases, the pupil diameter increases.

1. Draw a functional block diagram of the light-pupil system indicating the input, output, and intermediate signals; the sensor, the controller; and the actuator. (Section 1.4: Introduction to a Case Study]
2. Under normal conditions the incident light will be larger than the pupil. If the incident light is smaller than the diameter of the pupil, the feedback path is broken (Beehhoefer. 2005). Modify your block diagram from Part a. to show where the loop is broken. What will happen if the narrow beam of light varies in intensity, such as in a sinusoidal fashion?
3. It has been found (Bechhuefer. 2005) that it takes the pupil about 300 milliseconds to react to achongc in the incident light. If light shines off center to the retina, describe the response of the pupil with delay present and then without delay present