Study Questions: Light/Dark Adaptation

1. How does the visual system maintain a high sensitivity to stimulus contrast over a wide range of absolute levels of illumination?

2. What is "dark adaptation"? What are the labels on the axes of a dark adaptation function?

3. Sketch a typical dark adaptation curve when a subject is tested with (a) a small, red flash presented in the fovea; (b) a small, violet flash imaged far from the fovea; and (c) a very large, violet spot.

4. Based on 3(c), name at least three differences between near-threshold vision during the early times in adaptation (the first part of the curve) and late times (the second part of the curve).

5. Compare the characteristics of spectral sensitivity of the scotopic and photopic systems.

6. Describe the "Purkinje shift". Why does this happen? Describe the "Stiles-Crawford effect".

7. What is "light adaptation"?

8. Distinguish between neural (or field) adaptation and photochemical (or bleaching) adaptation.

9. What is an "afterimage"? Distinguish between positive and negative afterimages.