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Searching Science: How the Brain Finds What You're Looking for

A target-locating test from Science Buddies



George Resteck

Key concepts
Visual search
Perception
Distractions
Reaction time

Introduction
Have you ever wondered what makes you notice a certain person or object when you're rushing along in a crowd? Why do some things stand out whereas others melt into the background? In this activity you can explore the psychology of how things get noticed by studying how our brains help us perform a visual search. Specifically, you'll look at how changing the number and type of visual distractions affects a person's ability to find what they're looking for.

Background
Have you ever looked for something you really need to find—quickly? The classic example is when someone loses a set of keys. This frustrating situation is the perfect example of performing what cognitive psychologists call a visual search. During a visual search, an observer (the person who is searching for the keys, for example) looks for a target (the keys) in the midst of distracters (all the other stuff in a home). By making the target easier to see, such as by putting the keys on a big, bright red key chain, the observer could improve on their visual search and improve its chances of success.

What properties are important for performing a successful visual search? Consider the following exercise to help you think about the variables: If you had a printed page full of letter L’s in blue ink and just one letter T in red ink, it would be pretty easy to find the red T, right? However, what if half of the L’s were blue and half were red? In the latter situation, there are more complex distracters, making finding the target (the red letter T) more difficult.

Materials
• Computer with Internet connection
• Piece of paper and pen or pencil
• At least three volunteers (including yourself)

Preparation
• In your Web browser, go to the Cognitive Science Visual Search Web page developed by cognitive psychologist Tom Busey of Indiana University Bloomington. (Depending on what Internet browser you have and whether Java is enabled on your computer, you will either need to run the Java applet directly from the Web page or download the software to your computer. To use the Java applet, simply select the "Run Applet" button. To download the software, click on the movie link and follow the instructions to download the software to your desktop.)
• In the Visual Search applet or downloaded program, select the "Targets" tab at the top. In the "Target 1" section click on the large drop-down menu and select the image of a hot dog (the images are arranged alphabetically). The hot dog image should appear in the box after selecting it. Make sure the box next to "Display Target 1" is checked.
• Now click on the "Distracters" tab at the top. In the "Distracter 1" section, click on the large drop-down menu and select the image of a burger. The burger image should appear in the box. Make sure the box next to "Display Distracter 1" is checked.
• Next click on the "Do Experiment" tab. Make sure the "Use Circular Display" box is unchecked! Click on the "Start Experiment" button when you're ready and follow the instructions, pressing "f" if you see the hotdog or "j" if you do not see it. Tip: Make sure nothing distracting is going on when you do the experiment!
• After you are done it will tell you to click on the button below to quit and view your results, which will show up on the "Do Experiment" screen. Do not worry about your results quite yet. Instead, do the experiment one or two more times, or until you feel comfortable with the system, and then move on to the procedure below.

Procedure
• After you have tried doing the experiment with one distracter a few times and feel comfortable with it, do the experiment again.
• This time when you get the results of the experiment, write down the numbers in the "Mean Reaction Times for Target Present Trials" and "Mean Reaction Times for Target Absent Trials" boxes under "All Trials." (Ignore the numbers in parentheses.)
• Go back to the "Distracters" tab at the top. In the "Distracter 2" section, click on the large drop-down menu and select the image of a pizza slice. Check the box next to "Display Distracter 2."
• Click on the "Do Experiment" tab and run it by clicking "Start Experiment" and following the instructions.
• When you get the results of the experiment, again write down the numbers in boxes in the "All Trials" section. Did it take you more or less time to react with two distracters compared with one?
• Go back to the "Distracters" tab and add a third distracter, this time a peach. Do the experiment and again write down the relevant reaction time numbers. Did it take you more or less time to react with three distracters compared with one or two?
• Go back to the "Distracters" tab and add a fourth distracter, this time a carrot. Run the experiment again and write down the relevant reaction time numbers. Did it take you more or less time to react with four distracters compared with fewer ones?
Overall, how did the reaction time change as more distracters were added? Is this what you would have expected? Did it take longer for someone to react when there was a target present or absent?
• Repeat this activity with at least two other volunteers so that you have tested it with a total of three different people. For each person, be sure to let him or her try the experiment with only one distracter a few times before you start collecting the numbers from their experiments. For each volunteer, did you see the same correlation between reaction time and number of distracters?
Extra: Repeat this activity but try changing some different variables and see how it affects reaction time and the percent of the answers that are correct. You could try changing the number of targets instead of distracters. Is it easier or harder to spot multiple targets? You could also measure percent correct instead of response time. Do people give fewer correct answers as more distracters are present? Try changing the number of images by changing the number of rows and columns. Is it harder to find the target when there are more images? You could also try changing the images, such as using symbols, letters or numbers instead of types of food, or change the colors of the target and distracter. Is it harder to find the target as its similarity to the distracters increases?
Extra: This cognitive test has real-world applications that you could investigate. Look into how logos and brand names are designed to be noticed, the way Web sites are designed to be easy to navigate, how points of interest on a map are marked or other data are displayed in a way that highlights what's important. How are visual search properties used in these different areas?


Observations and results
Did the reaction time increase as more distracters were added? Did it take longer for volunteers to answer when the target was absent compared with when it was present?

You should have seen that, in general, the reaction time needed to do the visual search increased as more distracters were added. (There may have been some exceptions, such as a person taking only slightly longer to do a visual search with three distracters present in comparison with four, but it should have clearly taken a good deal more time to find the target when there were four distracters compared with when there was just one.) When more distracters are present, it makes finding the target more difficult. (Think of the example with the red letter T target and letter L distracters that became more distracting when they changed from all blue to half red.) This makes people take more time in their visual search, even if the target is not there. In fact, you should have seen that people actually take more time when the target is absent compared with when it is present, as they may spend more time checking and rechecking to make sure that the target is really not there.

More to explore
Cognitive Science Software: Visual Search, from Tom Busey at Indiana University Bloomington
Research Explains How the Brain Finds Waldo, from ScienceDaily
The Truth Behind Where's Waldo?, from ScienceDaily
The Brains Behind Where's Waldo?, from Science Buddies



This activity brought to you in partnership with Science Buddies

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