Name: ______Date: ______

Nervous System Lab: Measuring Reaction Time

Purpose:

  • To measure and compare response times for visual, auditory, and tactile stimuli.
  • To determine the different factors which affect reaction time.

Materials: meter stickblindfoldcalculator

Background Information:

Our ability to physically react to a stimulus is made possible by the nervous system. The nervous system receives and relays information about activities within the body and responds to internal and external changes.

The nervous system is divided into the central nervous system, which consists of the brain and spinal cord, and the peripheral nervous system, which consists of the cranial and spinal nerves and ganglia. The peripheral nervous system is further divided into a motor division and a sensory division.

A quick and simple reaction to a stimulus such as catching an object that is dropped in front of you, involves the complex interaction of various divisions of the nervous system. Your eyes first see the object dropped. Sensory receptors in your eyes, as part of the peripheral nervous system, transmit impulses to the central nervous system. The central nervous system then sends an impulse through the motor division of the peripheral nervous system to the effectors, causing your muscles to move your arm to catch the object. Although reactions such as these are extremely fast, various factors can affect your reaction time. In this laboratory investigation, you will measure reaction times to different stimuli.

Comparing Response Time for Different Stimuli

Procedure:

1. One person in the group will place his/her arm on a flat surface, such as a desk top. The hand should extend over the edge of the desk.

2. The partner will hold the meter stick so that the end of the stick is between the thumb and forefinger. There should be a space so that the meter stick can move between the fingers.

3. The person holding the meter stick will drop it without warning and the person withhis/her arm on the desk will grab the stick as quickly as possible. This will be donefive times for each test situation.

4. The person releasing the stick will record the point on the meter stick that the test subject grabs. This number in centimeters is then recorded in the chart.

5. There are three test situations. The first is visual, which means the test subject will watch and react as soon as the stick is released. The second test is auditory. The test subject is blindfolded and will respond when the tester says, “Now!” as the meter stick is released. The third test is tactile. The test subject is still blindfolded, but this time the tester will touch the person on the shoulder when the stick is released.

6. Obtain data for both partners.

Table 1. Response to Different Stimuli (Measured in cm)

Stimulus / Trial 1 / Trial 2 / Trial 3 / Trial 4 / Trial 5 / Average
Visual
Auditory
Tactile

Analysis:

1. Explain the relationship between the distance you measured on the meter stick and reaction time.

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2. What was the independent variable in this experiment? ______

3. What was the dependent variable in this experiment? ______

4. How does this experiment show the importance of running multiple trials? ______

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5. Which stimulus resulted in your quickest response? ______

6. Based on your answer for #5, why do you think this is the case? ______

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7. For each of the other two stimuli, provide a reason for the slight delay in reaction time (one reason for

each). ______

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8. How would you expect the data to change from the first to the last trial in any of the situations you tested? Why?

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9. Using the grid on the next page make a single graph that shows all of your results. Your graph must include a title, a proper scale, labeled axes and a key.

Real-World Application:

1. Describe two professions in which quick reflexes are necessary and why. ______

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2. Alcohol and marijuana are depressants. These are chemicals that slow the activity of the nervous

system. Why is it dangerous for a person to drive a car under the influenceof either of these

substances? ______

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3. Do you think it is possible for a person to decrease his or her reaction time (i.e. react quicker)? Does

any evidence from your lab support your view? Explain. ______

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4. You can easily calculate your response time using the following equation:

d = ½ at2

distance = ½ (acceleration due to gravity)(time squared)

If we solve for t, you can calculate your reaction time. Fill in the numbers to get your average reaction time.

t =

d = distance measured on the meter stick (convert to meters first!!!!!)

a = 9.80 m/s2(acceleration due to gravity – it’s a constant)

t = reaction time (what you are solving for!)

Your average reaction time: ______

5. In the space below, draw a picture of the pathway that the “signal” took through your nervous system, starting from the point of the stimulus and ending with you catching the meter stick. You can use any method to visualize this process that you would like. Make sure to label your diagram(s). I showed you an example of a “voluntary pathway” through the nervous system in class…you could use that as a model. You should include in your diagram: sensory nerve, motor nerve, brain, and spinal cord.

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