Name _______________________________________ Date __________________ Period ____________ R EACTION T IME Background Information In humans, and indeed, in any other vertebrate, there are myriad ways that the body may be controlled. Hormones can be released into the blood to alter heart rate or venous dilation, and nerves can send signals to slow down digestion or allow for the fingers to play the piano. At any given moment in the body, there are thousands of signals being sent in these, and other, formats. However, the brain need not be involved in all of them. Indeed, there are a great many instances in which brain involvement might mean injury or death. Take, for example, touching a hot object. When the object is touched, the hand will automatically jerk away, and only after that will you feel pain and run for cold water. This reaction did not involve the brain, but rather the spinal cord (see figure 1 below). When we speak of reaction time, we are not referring to this kind of reaction. The hot object reaction is not readily measurable for obvious safety reasons, and, as it involves no higher brain function, is not generally variable between individuals and is not affected by environmental stimuli. Properly defined, reaction time is the time that it takes for your eyes to notice that something is happening, then for your brain to calculate an appropriate response, and the for your muscles to execute that response. Because this pathway (see figure 2 below) does involve higher brain function, it will vary between people and with environmental stimuli. It is this second nerve pathway that interests us today. You will be testing your labmates’ reflexes by dropping a meter stick and having them catch it. Because this activity is not “reflexive,” it will give us a good idea of who in the class has the quickest neurons. We will introduce some variables (one at a time, of course!) later in the experiment after we have established a control. Materials Meter stickGraphing program Lab partnerData sheet BRAIN HOT!!! Spinal cord Sensory neuronMotor neuron Movement of hand EVENT Sensory neuronMotor neuron Response Fig. 1. The spinal reflex arcFig. 1. The sensory nerve pathway

Procedure 1.Gather all your materials, and go to a lab bench away from other groups and distractions 2.One partner will hold the meter stick so that the zero centimeter mark is between the thumb and pointer finger of the dominant hand of the other partner. Your dominant hand is the one with which you write. 3.Without warning, and at random, the partner holding the stick will release it, and the other partner should try to catch it as soon as possible. 4.Record the distance that the stick fell by seeing where it was grabbed by the partner who was catching. 5.Repeat this procedure ten times for each partner, for a total of twenty drops. 6.Now that a control has been established, we will introduce one variable. We will repeat the procedure above, but with “distractions.” This means that the person doing the catching needs to be unable to focus completely on the task at hand. I leave it in your capable hands to devise a scheme for distracting each other. Remember, nothing illegal, flammable, explosive, corrosive, dangerous, smelly, disrespectful, irreparable, emotionally-scarring, or pointy. 7.Pick the best graph style, and plot your data neatly and accurately. Remember to include axis labels, a legend, a title, and an appropriate scale. Results Distance without distractions Distance with distractions Average distance: Average time: Average distance: Average time: Reaction time = Where s is the average distance and a is the acceleration due to gravity. 2s a Show your calculations

Compile the data from the entire class, and plot that as well. Include everything that a good graph should. It is now time to put the scientific method to work! In this section, you need to devise your own experiment, using any available materials, and containing a control and only one variable. Some items that you may with to investigate could include: caffeinesleepblindfoldsearplugs sittingstandingexercisemood timerepinephrinenoisemusic other handfootboth handsclose one eye temperaturetarget pointrhythm counting For this portion of the experiment, you need to create your own data sheet and collect your own data. You may wish to model yours on the one provided, or craft one of your own to best suit your particular experiment. Record your hypothesis here, and write your procedure and collect your data on your own slice of paper. Hypothesis and up and up No. of people – without distractionsNo. of people – with distractions

Conclusions 1. Did distractions produce longer or shorter reaction times? 2. Explain your answer for number one. Include information about the nervous system. 3. What impact might this type of research have on people who work in crowded or noisy areas? 4. What other factors aside from distractions do you think might affect reaction time? 5. For your experiment, do your results support your hypothesis? Explain. 6. What conclusions can you draw from your experiment? 7. Identify at least three potential sources of error in your experimental setup. 8. If humans had evolved on a planet with more gravity, how do you think our reaction time might have been affected? 9. What physiological changes would you make to increase your reaction time?