Nature Science Knowing Nature Assignment
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Knowing Nature, Fall 2021
Homework 1 – 45 points total
Overview: We are using the topic of human color vision as a way to reflect on “direct” perception, subjectivity and objectivity, measurement, and representation. The readings contain a lot of detail on the physics of color perception, but this homework assignment is intended to focus your attention on the skills and themes that are most relevant to the class.
Readings/listenings/viewings:
1. Radiolab episode on color – the first 10 minutes is excellent for giving background that will help with the readings, and the rest relates directly to themes from class.
2. Draft “Color” chapter by Kathryn Schaffer (part of a book on light) – on canvas
3. Very short youtube video on bees and crab spiders and UV light: https://www.youtube.com/watch?v=UjHvs5Xz_TI
Please answer these questions on this sheet or another sheet of paper. Note that some questions do not have single “right answers.” Also be sure to use your own words and avoid paraphrasing any research sources for these answers.
1. (3 points) In class in week 2, we used spectroscopes to study different types of “white” light, including fluorescent light, flashlights, and light from the sun. Combining what we did in class and what you learned from the readings, is there a way to explain what “white” light is, in terms of the underlying wavelengths that are part of the light? Explain, referring to empirical evidence in your answer.
2. A person looks through a spectroscope at two light sources. When they look at light source A, they see a complete rainbow across the display, showing light at every visible wavelength, with equal brightness. When they look at light source B, they see one bright band at around 450 nm (“blue”), one bright band at around 500 nm (“green”) and one bright band at around 650 nm (“red”). The three bands are equally bright.
(a) (4 points) Draw spectrum graphs to represent these different measurements, in the same way as we discussed in class, and in the same way as the graphs on page 190 of the readings. Label them A and B to show which is which!
(b)(2 points) Speculate on how you think a human eye (without the spectroscope) would see these two types of light. Do you think they would be visibly different? Visibly similar? Why?
2. (3 points) In class in week 2, we looked at examples of “color illusions” and “color constancy.” Pick one of these topics, and explain why it shows that the color a human perceives is not an “objective” property of things.
3. One variant of color blindness in humans occurs when a person is missing L cones, and only has S and M cones.
(a) (2 points) Draw a graph that represents the wavelength sensitivities of such a person’s cone cells (in other words, draw a graph that is similar to the one on page 193 of the readings, but appropriate for an eye with no L cones).
(b) (3 points) Using the graph you have drawn, explain in words what happens when a person with this type of color vision senses “green” light (with a wavelength of around 500 nm) and what happens when the person senses “red” light (with a wavelength of around 650 nm).
(c) (3 points) How is this different from how a non-color-blind human eye would eye would respond to light at those two wavelengths? Would you expect these differences to translate to differences in perception?
5. Many areas of scientific research, including climate science, use sensors to detect light and analyze it according to wavelength components. For example, instruments called radiometers, mounted on a satellite flying several hundred miles above the Earth’s surface, receive incoming light that has been reflected by clouds, plants, atmospheric particulates, etc. The Multi-angle Spectroradiometer (MISR) instrument, as one current example, receives reflected light in 4 wavelengths (446nm, 558nm, 672nm, and 866nm). The instrument is very sensitive and records the intensity (“amount”) of light received at each wavelength. It then sends these data back to Earth. A scientist then takes these data and, using the numerical values of intensity at each of the 4 wavelengths, measured at each location across a field of view, creates a composite image like the one on the next page.
(a) (5 points) Compare and contrast this type of “observation” and the process by which a human looks at an object and judges it to be yellow. You should include examples of ways that it is similar and ways that it is not similar.
(b) (2 points) Does this MISR instrument measure “color”? Please discuss.
(c ) (5 points) In every form of measurement that we make, there is always a human at the end interpreting the information. A human viewing an object directly might interpret their sensations as “bright red.” A human viewing an image from a remote sensing system might interpret it as showing “more light in the infrared range of the spectrum than the visible.” Is the person making the same kind of interpretive judgments in either case, or are they different? Discuss, incorporating themes of objectivity and subjectivity as discussed in class and the readings.
(d) (2 points) Is it possible, in your view, to remove subjectivity entirely from the process of measurement and interpretation? Use the example of a scientist viewing a remote-sensing image to explain why or why not, in your opinion.
The image above is an example of a composite image made from MISR data. Data from each type of sensor has been given a different color and they have been merged together into one image.
6. (4 points) According the Radiolab clip you listened to, when Isaac Newton used a glass prism to “divide”white light into a spectrum of wavelengths we see as a rainbow of colors, there was some question about the actual role of the scientific device – the prism – and what it was doing. What was the concern and how did Newton test the effect/role of the prism in generating a rainbow?
7. In the Radiolab section you listened to the interviewer Robert Krulwich asks a “visual ecologist” the following: “If a dog, and a human, and a crow were staring at rainbow, would they be seeing very different things?” The visual ecologist answers: “Yes.” Watch the following video, which is about a similar kind of situation:
As the video explains, flowers appear differently in reflected visible light and in reflected ultraviolet (UV) light. Bees apparently use these differences to navigate towards nectar sources.
(a) (2 points) Looking at the illustration on p.198 of the “Color” chapter you read, what numerical range of light (in “nanometers / nm” is the bee likely seeing reflected off the crab spider that the an animal like a bird or human is not?
(b) (2 points) The narrator in the video points of that the spider is white colored on a white flower and so “looks supremely camouflaged.” Camouflage is a term used to describe a situation where a creature is trying to hide and NOT draw attention to themselves. What animal might the spider be hiding from in that case, and why?
(c ) (3 points) If humans can’t see ultraviolet light, how can we see “what a bee sees” in the image above? Explain briefly how a “ultraviolet camera” must work to make a image like the one above.
extras/drafts
7. In the Radiolab section you listened to the interviewer Robert Krulwich asks a “visual ecologist” the following: “If a dog, and a human, and a crow were staring at rainbow, would they be seeing very different things?” The visual ecologist answers: “Yes.” Watch the following video:
The narrator in the video points of that the spider is white colored on a white flower and so “looks supremely camouflaged.” Camouflage is a term used to describe a situation where a creature is trying to hide and NOT draw attention to themselves. What animal might the spider be hiding from in that case, and why?
If an animal sees reflected ultraviolet light, is flower appears differently:
Looking at the illustration on p.198 of the “Color” chapter you read, what numerical range of light (in “nanometers / nm” is the bee likely seeing reflected off the crab spider that the an animal like a bird or human is not?
If humans can’t see ultraviolet light, how can we see “what a bee sees” in the image above? Explain briefly how a “ultraviolet camera” must work to make a image like the one above.
WK2 HW QUESTION on Remote Sensing:
An instrument called a radiometer, mounted on a satellite flying several hundred miles above the Earth’s surface, receives incoming light that has been reflected by clouds, plants, atmospheric particulates, etc. The Multi-angle Spectroradiometer (MISR) instrument, for example, receives reflected light in 4 wavelengths (446nm, 558nm, 672nm, and 866nm). The instrument is very sensitive and records the intensity (“amount”) of light received at each wavelength and sends these data back to Earth. A scientist then takes these data and, using the numerical values of intensity at each of the 4 wavelengths, creates a “true-color image” like the one below.
(a) How does this way of “observing” compare and contrast to the process by which a human looks at an object and judges it to be yellow? You should include examples of ways that it is similar and ways that it is not similar
(b) Does this MISR instrument measure “color”? Please discuss.
Comment by Kathryn Schaffer: This is a rich question… but since the chapter reading doesn’t really deal with imaging, I am not sure what we are driving at in this particular context
(c) Does the MISR instrument take a picture? Please discuss.
(d) For every observation – a human interpretation is necessary to convert received information into usable data. For example, at the 866nm wavelength, the MISR satellite “sees” live vegetation as being very bright (it has a high brightness intensity at 866nm wavelength). A human might show these data as “bright red” on a graph. However, plants appear “green” to the human eye. Explain the difference and be sure to incorporate themes of objectivity and subjectivity from the reading, our discussions in class, and your understanding of how “observations” are made. Comment by Kathryn Schaffer: I am sort of worried that this question mixes two ideas… in my version I was going for a comparison between the act of subjectively judging color, and the act of comparing “objective” instrument measurements. But this question also invokes the representation choices we use to display non-visible colors, which I think is kind of another topic. Hope that makes sense?
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