A typical major-league pitcher can throw the ball over 90 miles per hour (145 km/hr). For a batter standing 60 feet 6 inches (18.3 m) from the mound, that leaves less than half a second to react! No wonder hitting a baseball is considered one of the toughest challenges in sports.

A stimulus is anything that can cause a reaction. When you sense a stimulus, an electrical impulse travels from the sense organ through your nerves to your brain. After a decision is made, other impulses travel from your brain to various muscles, and you respond.

In some cases, the nerve impulse does not need to be interpreted by your brain for you to respond. These reactions are called reflexes and happen much more quickly than conscious decisions. Some of the factors that influence the reaction time for these reflexes can be investigated with this Gizmo™.

## Measuring Reaction Time

In this activity you will measure your reaction time to two different stimuli, one visual and one audible. You will then compare these reaction times.

1. On the SIMULATION pane of the Gizmo, check that the Sight test is selected. Choose a shape and color from the dropdown menus (Circle and Red are the defaults). When the test begins, you will click your mouse button whenever the shape appears on the screen (it will appear 10 times). Click Start, and complete the test.
1. What was your average (mean) reaction time?
2. What was your fastest reaction time? Slowest? Did you make any mouse-clicking errors?
3. The range of your reaction times is equal to the longest reaction time minus the shortest. What is the range of reaction times in this test?
4. Standard deviation is a measure of how spread–out your data is. It is a more complete description of the spread of the data than the range because it takes into account every data point, not just the extremes. What was the standard deviation for this test?
5. If your data has a normal distribution (following a bell-shaped curve), then about 68% of the values should fall within one standard deviation of the mean. (This is much more likely to occur when the sample size is large.) Of the ten reaction times that were recorded, how many are within one standard deviation of the mean?
2. Click New exam, and select the Sound test. Choose a sound from the dropdown menu, and check that your computer's audio is turned on. (Headphones are recommended if you are working in a lab setting.) Click Start, and complete the test.
1. What was your mean reaction time to a sound stimulus?
2. What was the fastest reaction time? Slowest? What was the range of these reaction times?
3. What was the standard deviation for the sound test?
4. Select the TABLE tab. How did the mean reaction time for the sound test compare to the mean reaction time for the sight test? How did the standard deviations compare? (Note: If you wish to export this data to a spreadsheet, click Export and then paste the data into the spreadsheet.)
3. Try additional Sight and Sound tests with various shapes and sounds. You can also take a combined Sight and Sound test if you wish. View the results on the GRAPH tab.
1. Were your results consistent? Was one type of reaction time always faster than the other?
2. Did reaction times improve as more tests were taken? Do you think you could significantly improve your reaction times with more practice? Explain why you think this is.
3. Reaction times are partly determined by how far the nerve impulses must travel, as well as how many nerve junctions must be crossed. Based on your results, which nerve pathway is more direct, the path for auditory responses or the path for visual responses? Explain.
4. Write an overall conclusion for this activity. Based on your experiments, what did you learn about reaction times to sight and sound stimuli?

## Creating a Science Fair Project

This Gizmo can be used in a science fair project or other experiment. If you decide to try this, the first challenge is to come up with an interesting question to investigate. Here are a few ideas.

• Which is generally faster, our reaction to sights or our reaction to sounds?
• Does age affect reaction times? If so, by how much?
• Does gender affect reaction times? If so, by how much?
• Do athletes have better than average reaction times? How about avid video game players?
• Does what we eat or drink affect reaction times? (You can test substances like sugar and caffeine, for example. If you are testing adults, you can even explore the effects of depressants like alcohol on reaction time.)
• Can reaction times improve with practice?
• How do various distracters (flashing lights, loud noises, people talking) affect reaction times?
• How does the amount of sleep affect reaction time? Does getting a good night's rest lower reaction times?
• Does body temperature affect the rate at which nerve impulses are transmitted? (Brave participants can have their arms soaked in ice water or warm water before undergoing the experiment.)