Perception
Psych 293
Spring 2015
Exam 1 Answers
There were 150 points on the exam as a whole — 10 questions worth 15 points each. You earn points on each question starting at zero. A score of 7 or 8 means you got the question about half right. Those are positive points. A score of 10 means you got a lot of it right. A score of 12 – 14 means you missed just a little bit. And 15 is full credit on a question. On each page, the scores for each question are added, so you will see a total for the page. Those are added up on the back page.
1. The graph of the sodium vapor lamp is like one of the narrow band street lights we talked about. The two wavelengths are very, very close together. A blue filter is called a blue filter because it looks blue. It looks blue because the wavelengths that get through it to your eye are the wavelengths that typically look blue. That is the short wavelengths. The wavelengths in this graph are NOT short. Therefore, they cannot get through. No wavelengths come out the other side. A magenta filter passes both long and short wavelengths and absorbs the middle. The long wavelengths that get through might include these. They might not. You can say either one. If this light gets through, it has to be these wavelengths because there are NO OTHER wavelengths around. What comes out the other side has to be either these wavelengths or none at all.
2. Newton was making a distinction between physical properties of light and psychological experience (color). He did not know as much about the physical properties of wavelength that we know today, but he set the stage for future discoveries. But he insisted that whatever the relevant physical properties of light were, they were strictly physical and not psychological. The word “color” for him meant only the psychological experience. He thought that the physical processes caused the psychological experience, but were not at all the same thing.
3. This question asks you to use the rgb computer coding system that you did a homework on. For every pixel, the amount of red, green, and blue primaries is indicated between 0 and 255. A pure red color is indicated as (255, 0, 0) — all red and no green or blue. Green is (0, 255, 0). Blue is (0, 0, 255). The complement of red is cyan — (0, 255, 255). The complement of green is magenta (255, 0, 255). The complement of blue is yellow — (255, 255, 0). If you have a color and its complement, you get (255, 255, 255), which is white. In all cases. of a primary and its complement. So you can see your knowledge about how primaries and complements work illustrated in the numbers. The rgb units on the computer are NOT identical with wavelength. You do not automatically know the exact wavelength mixture when you know the rgb units. You do not the psychological colors well enough to get the additive mixing results that you should.
4. Because this is a graph of a filter’s characteristics, the high numbers show wavelengths that are passing through it and, hence, giving it its color. The low numbers show the wavelengths that are mostly blocked. This graph is high in the middle and long wavelength regions and therefore should be yellow. If you say orange or mention that it is a combination of long and some middle, and give a reasonable color name, you would get most of the credit.
5. In order to say that something is an illusion, there must be a comparison to something that is NOT an illusion. If there is not such contrast, then everything could be an illusion, or nothing. Many of you talked about the role of past experience. That only speaks to the point if there is a reason for the past experience to not be illusory. Past experience could be illusory.
6. “A ray of light is a ray of light” is the most apt truism. The implication is that there is no difference in light itself at the eye between light coming directly from a source and light reflecting from a surface. Yet we see solid surfaces as solid surfaces. That is a problem (for future consideration). How do we know that light has been reflected from a surface (allowing us to see a surface) if light at the eye is just light?
7. The diagram shows 3 lights on the left, a red, green, and blue. When all 3 (primaries) are on, the light is white. That light then is set to pass through 3 possible filters. The question asks you to indicate which of the 3 filters (cyan, magenta, and yellow) should be used in order to make the final beam of light red. Then it asks why. The answer is that the magenta and yellow filters need to be on and the cyan filter off (not used). Reasons? The magenta filter takes out (absorbs) middle wavelength light and passes long and short wavelengths. That leaves long and short wavelengths getting to the yellow filter. The yellow filter takes out (absorbs) short wavelengths, so once the light has passed through that filter, what remains is red (long wavelength) light. Keep in mind that all a filter can do is block light or allow it to pass through. It cannot add anything. Then, if you mention any set of lights on the left that includes red, and a filter that passes red, you would have answered the last part of the question.
8. When lights of various wavelengths are mixed in the same area, we get additive mixing. That literally is mixing. Subtractive processes (colored material, colored filters) only take away wavelengths (that had to be present first). People with experience with paint, see literal mixing of paint so they talk about it as color mixing. That makes perfect sense. However, it is misleading because the coloring process with paint is all subtractive. Yellow paint is yellow because it is subtracting out short wavelengths and reflect middle and long to the eye. When blue-green paint is added, the long wavelengths are subtracted, leaving only middle wavelengths to get to the eye. Thus, in one case the mixing is of the lights, in the other case it is paint. So what is “mixing” is different in the two cases. For understanding vision, this is extremely misleading to think the word “mixing” is being used the same way.
9. Yellow is not a primary color according to what you know so far because it can be made of two other primaries, red and green.
10. Metamers are cases of colors that look the same but are made up of different component wavelengths. Wavelength and color are distinguished in metamers because metamers are colors that are the same, but that have different wavelengths giving rise to them. Thus, there would be two or more different wavelength combinations but one color. It does not make sense, here, to say that in metamers a color is made of several different constituent colors. You MUST refer to wavelength as the constituents and to colors as what you actually see. If you use the word “color” in both cases, you miss the essence of the distinction between wavelength and color. If color and wavelength were the same thing, then for every difference in wavelength combination there would have to be a different color experience. But that’s obviously not the case because there are so many cases in which different wavelength combinations look the same.