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Are Your Eyes Playing Tricks on You? Discover the Science Be

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Melissa Alexis

on 25 July 2014

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Transcript of Are Your Eyes Playing Tricks on You? Discover the Science Be

I've concluded that my hypothesis was correct. My results showed that the longer the colored image was viewed, the longer the afterimage would last. For 10 seconds the average amount of time the afterimage lasted was 13 seconds and for 60 seconds the average was 55 seconds, so that shows it lasted longer.
Thank you for watching!!
An afterimage is an impression of a vivid sensation (especially a visual image) retained after the stimulus has ceased. There are special sensory cells in our eyes called cone cells. "Scientific American" says that there are three different types of cone cells (each of them respond to red, blue, and green light). The different cone cells are stimulated so that you can see other colors, which are mixtures of red, blue or green. When you look at a color for a long time, your cone cells get fatigued or tired and they do not respond, which is how an after image is formed. After several seconds, your cone cells will recover. The afterimage will fade away, and you will see normal colors again.
In this experiment, I will be looking at a colored image for a certain amount of time. I'll have a partner to record the time for me. Then I will look to the white space to the right and look at the after images. After doing all the trials i will record my results in my lab notebook.

If you stare at a colored image for a long time, then the afterimage will last longer because cone cells in your eyes will become more fatigued so it will take longer for them to recover.

Computer with a color monitor, or you can print the figures out on a color printer
Stopwatch or a clock or watch with a second hand
Lab notebook
Colored pencils or a basic computer graphics program

Part 1: Duration, Shape, and Color of an Afterimage
1) Look at Figure 1, below. Have your helper get ready to time you for exactly 30 seconds. You should say "start" when you begin looking at the object, and the helper can say "stop" when 30 seconds have elapsed.
2) Stare at the red circle for 30 seconds. Try not to blink. When 30 seconds are up, look at the white space in the square to the right. Describe the size, shape, and color of the afterimage in your lab notebook. Note: It is important to view this on a bright monitor with clear colors, or if you printed it out, that the color is vivid.
3) Turn off any lights near your computer or the printed-out image. Stare at the red circle for 30 seconds again, but this time, record how long the afterimage is visible in your lab notebook. Have your helper use the stopwatch to keep track of how long you are able to see the afterimage. You might want to say "start" as soon as you begin looking at the white space and keep saying "I still see it" repeatedly until it disappears, then say "it's gone" so your helper can stop the stopwatch and you can note the time. Why does the afterimage disappear?
4) Repeat step 3 two more times, for a total of three trials, and record all data in a data table in your lab notebook, like Table 1, below. Note: Give your eyes a minute or so to rest between every trial.
5) Repeat steps 3-4 four more times, changing the amount of time you look at the red circle each time. Look at the red circle for 5, 10, 20, and then 60 seconds before you look at the white area (you already completed the 30-second trial in steps 3-4).
6) Record how long the afterimage persists after each time in your data table.
7) Calculate the averages and insert that data in the last column.
8) Graph the data. Put the number of seconds you looked at the object on the x-axis and the average time the afterimage persisted on the y-axis. Call the x-axis Cone Stimulation and the y-axis Afterimage Persistence, or choose your own axis names. Include the units (seconds) on the graph.
9) What was the maximum amount of time that the afterimage persisted?
10) If you stare at the object for longer periods of time, beyond 30 seconds (say 60, 90, and 120 seconds) does the persistence time of the afterimage also keep increasing? Explain your results in terms of the level of fatigue of the cone cells.

(n.d.). Retrieved July 18, 2014, from http://faculty.washington.edu/chudler/after.html

Are Your Eyes Playing Tricks on You? Discover the Science Behind Afterimages! (n.d.). Retrieved July 18, 2014, from http://www.sciencebuddies.org/science-fair-projects/project_ideas

Spooky Science: Discovering the Eerie Colors behind Afterimages. (n.d.). Retrieved July 18, 2014, from http://www.scientificamerican.com/article/bring-science-home-afterimages/

Cone cell. (n.d.). Retrieved July 22, 2014, from http://www.newworldencyclopedia.org/entry/Cone_cell

Are Your Eyes Playing Tricks on You? Discover the Science Behind Afterimages!

by : Melissa Alexis
The maximum amount of time the afterimage persisted was 36 seconds.
I did this lab to see how viewing a colored image affects cone cells in our eyes, and how it tires them. What I did during this lab was have volunteers look at afterimages for 5 seconds, 10 seconds, 20 seconds, 30 seconds, and 60 seconds. Each volunteer had to make sure they blinked as little as they could.
If they blink a lot, that give their cone cells a break, which affects how long the afterimage will last. For the red circle afterimage, it turned out to be the same size and shape, but the color was light blue. All my volunteers got around the same times. At the end, I got all the results I expected.
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