All essays were graded anonymously (by covering the name at the top of the sheet).

Each question was graded separately.

The maximal score for each question was 10 points. To receive 10 points an essay did not have to include all the information we discussed on the topic, but it did have to include enough clear and accurate information that someone reading the essay would understand most of the important points we covered.

Most essays received partial credit as a result of including incomplete or inaccurate information.

To determine your total points for this exam, add up the three scores for the three questions. The maximal number of points for this exam is thus a total of 30.   (Check the distribution of grades for this exam.)

To receive a straight B for the semester, you should earn a total of 90 points (an average of 18 points on each of 5 exams).   To receive a straight C, you should earn a total of 60 points (an average of 12 points on each of 5 exams).   At the end of the semester I also examine everybody's scores and award some extra credit for consistent improvement on exams (especially after the first exam).   The target for a B is subject to adjustment by me at the end of the semester.   The target for a C is engraved in stone!

If you would like me to regrade your exam, return your exam (all three questions) to me with a separate note about what you feel needs correcting before the next exam.

Most important ... I will be glad to talk to each of you about any exam. Good times are immediately after class or later in the afternoon (see me after lecture to arrange a time).


1. Describe a study of habituation.

Most essays used the sea slug (Aplysia) gill-withdrawal reflex or the Coolidge effect as an example of habituation.   A good essay used the terms for the key features correctly (habituation, recovery, dishabituation), provided definitions, and explained how the example illustrated these features of habituation. The Coolidge effect caused some confusion in many essays especially in defining and explaining dishabituation..

2. Describe how bats fly in total darkness.

Many essays correctly described Spallanzoni's early (1700's) experiment which showed that bats use hearing to fly in total darkness.   Good essays explained echolocation and the importance of high frequencies for echolocation.   The equation relating wavelength to frequency and the importance of wavelength for detecting small objects were included in many essays, but only a few explained the equation and its importance clearly.   Also included in many essays, but often not fully explained, were the kinds of information bats obtain by echolocation and the experiments showing the limits of echolocation.

3. Describe the spatial resolution of an insect's eye.

This question was to some extent a variation on the theme of the preceding one.   The basic structure of an insect's eye is important to understanding its spatial resolution, and most essays explained this point.   The trade-off between small ommatidia and greater diffraction was clearly explained by only a few essays.   Many essays however had parts of the explanation: the equation relating diffraction to the diameter of the ommatidia and to wavelength; the importance of using short wavelengths; and the consequent arrangement of rhabdomeres for color vision.