Physiology Lessons Lesson 11 Reaction Time Fixed & Pseudo

© BIOPAC Systems, Inc. 2005

Physiology Lessons for use with the

Biopac Science Lab MP40

PC running Windows® XP or Vista or Mac® OS X 10.4 -10.5

Lesson 11 Reaction Time Fixed & Pseudo-random Intervals

Lesson Revision 11.26.2007

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Fig. 11.1

Lesson 11 Reaction Time

I. SCIENTIFIC PRINCIPLES

The beginning of a race is a classic example of a stimulus-response situation, where people hear a stimulus (such as the starter’s pistol) and react to it in some way (response). There are two key factors in stimulus-response: reaction time and learning.

• Reaction time is the delay between the stimulus presentation and the beginning of the response.

• Learning is the acquisition of knowledge or skills due to experience and/or instruction.

The delay between hearing the signal and responding is due collectively to the time for the sensory signal to reach the brain, the time required for the brain to process the sensory information and generate a motor response, and the time for motor signals to reach the skeletal muscles. With learning, the time for the various steps in the process can be shortened. Reaction time varies from person to person and from situation to situation, and most people have delayed reaction times late at night and early in the morning.

As people learn what to expect, reaction time typically decreases. Imagine a young man entering a track event for the first time. When the pistol goes off, he might not know what to do, but after everyone around him started running he would get the idea and start running as well. In the next race, you would expect him to start at about the same (although not exact) time as everyone else, assuming some learning took place in the meantime. With practice, and more importantly, learning, his reaction times could be cut from a few seconds to fractions of a second.

Note Some years ago, a world-class runner was repeatedly accused by his competitors of “jumping the gun” in races. He could only respond to these accusations by saying that he felt he had done nothing wrong. When footage of his races was reviewed, it became clear that he was in fact leaving the starting blocks before his competitors. As the evidence against him mounted, he underwent physiological testing which measured how long it took him to respond to external events or stimuli. It was revealed that his responses were some five to ten percent faster than those of an average runner, and this slight advantage enabled him to react faster once he heard the starter’s pistol

This lesson shows how easily and rapidly people learn, as demonstrated by their ability to anticipate when to press a button. The lesson uses a relatively simple variation of stimuli (pseudo-random vs. fixed interval) to determine what results in the shortest reaction times.

When fixed-interval trials are repeatedly performed, average reaction time typically decreases each time new data is recorded, up to a point. Eventually, the minimal reaction time required to process information is reached and reaction time becomes constant.

When pseudo-random presentation trials are repeated, it takes longer for reaction times to decrease and the decrease is less than as occurs with fixed-interval presentation.

Usually, longer reaction times are a sign that people are paying less attention to the stimuli and/or are processing information. That is, if it took you more time to respond to clicks while also reading a book than when you were also watching TV, then you could infer that you were probably paying more attention to the book than to TV since your brain took longer to respond. Deriving these types of measures from simple reaction time tests allows researchers a glimpse into the cognitive and neurological functioning of people as they perform tasks.

This lesson takes a relatively simple look at reaction time and how changing one small aspect of a procedure can result in differences in reaction times. You will probably notice a difference in average reaction times between the pseudo-random and fixed interval presentation trials, and this difference will most likely favor the segments with fixed-interval presentation of stimuli. Part of this difference is probably due to the random vs. non-random presentation of the stimuli. However, you might have also noticed that reaction time decreased from pseudo-random presentation to fixed-interval presentation, suggesting that maybe you just got better with practice.

In more complex investigations, people might be placed in two different conditions (e.g., happy vs. sad, watching TV vs. reading a book) and their reaction time for each condition would be measured. Variations on this theme present people with hundreds of stimuli, often in the form of words or pictures. Although not covered here, such investigations might measure the alpha-band EEG in addition to response time as another indicator of attention, and review the connection between reaction times and alpha-band EEG activity when people are paying attention to a TV program versus when they are relatively relaxed.

The process of changing the order of presentation for different groups of people is known as counterbalancing and is commonly performed in psychological, medical and other types of research investigations that use experimental

Lesson 11: Reaction Time Page 3


procedures. By comparing the reaction time difference between trials with differing order of presentation, you can see how learning contributes to reaction times.

In order to compare the reaction times from the two types of presentation schedules, you can summarize the results as statistics or measures of a population. There are certain statistics that are usually reported for the results of a study: mean, range, variance, and standard deviation. Mean is a measure of central tendency. Range, variance and standard deviation are measures of distribution or the “spread” of data. Using the statistics of mean and distribution, investigators can compare the performance of groups.

The mean is the average or the sum of the reaction times divided by the number of subjects (n).

The range of scores is the highest score minus the lowest score. The range is affected by extremely high and low reaction times, so investigators also describe the “spread” or distribution of times with two related statistics: variance and standard deviation.

Variance is determined by calculating the average squared deviation of each number from its mean.

Standard deviation is the square root of the deviance.

In this lesson, you will calculate your group statistics, but you will not do any formal comparisons between groups.

II. EXPERIMENTAL OBJECTIVES

1. Measure and compare reaction times of an individual subject using two stimulus presentation schedules: fixed intervals and pseudo-random intervals.

2. Introduce elements of statistics into data analysis.

3. Use statistics to determine the effects of learning on reaction times.

III. MATERIALS

Biopac Science Lab system (MP40 and software) on computer running Windows XP or Mac OS X

Electrode lead set (40EL Lead Set)

Feedback Set: Feedback cable (40CBLFB1) and stereo headphones (40HP)

Disposable vinyl electrodes (EL503), three electrodes per subject

Attention Windows Vista® users:

Audio Format menu > Advanced tab

Windows Vista® users must reset Griffin iMic Audio Properties

The iMic USB audio adapter defaults to 1-channel audio configuration. Lesson 11 Reaction Time requires 2-channel audio.

Prior to initial audio capture setup, the following steps are recommended to adjust the Audio setting.

1. Go to Start > Control Panel > Sound. 2. Click the 'Recording' tab and then double-click 'Microphone' to

open 'Microphone Properties'. 3. Click the 'Advanced' tab. 4. From the 'Default Format' menu, select “2 channel, 16-bit, 44100

Hz”. (48000 Hz will also work.) 5. Click 'Apply' and then click 'OK'. 6. In the 'Sound' dialog, click the 'Playback' tab. 7. Double-click 'Speakers' to open 'Speaker Properties'. 8. Click the 'Advanced' tab. 9. From the 'Default Format' menu, select “2 channel, 16-bit, 44100

Hz”. (48000 Hz will also work) 10. Restart the computer.


IV. EXPERIMENTAL METHODS

A. Set Up EQUIPMENT SUBJECT

Fig. 11.2 Feedback cable via computer

To Optional Adapter

Fig. 11.3 Feedback cable via adapter

red lead – bottom white lead – top black lead (ground) – inside wrist

Fig. 11.4 Electrode connections

FAST TRACK Details 1. Turn the computer ON.

2. Connect the feedback cable (40CBLFB1):

Blue to Line in, Green to Line Out

3. Connect the MP40 to the feedback cable (blue).

4. Connect stereo headphones (40HP) to the feedback cable (black).

5. Set the dial to OFF.

For direct connection to the computer, see Fig. 11.2.

For connection via USB Audio adapter, see Fig. 11.3. A variety of USB Audio adapters can be used. Yours

may not match the sample shown but the 40CBLFB1 connections should always be blue to Line in and greento Line out.

Note The extension cable (40CBLEXT) can be used between Line Out and the 40CBLFB1.

6. Attach three electrodes to the forearm and wrist as shown above.

Attach three electrodes to the Subject’s dominant forearm and wrist as shown in Fig. 11.4 to record activity of the extensor digitorum, the primary muscle (located in the posterior forearm) used to lift a finger.

The dominant side is generally the right if the subject is right-handed or the left if the subject is left-handed.

The extensor digitorum, located in the posterior forearm, is the primary muscle used to lift a finger.

The recording electrodes should be in the midline of the posterior forearm about 10 cm apart; the ground can be at the wrist.

To help define electrode placement: Place your hand on a table, palm down, then lift (extend) the middle finger (contract the extensor) and use your other hand to feel the bulge as the extensor contracts.

7. Connect the electrode leads (40EL) to the electrodes, matching lead color to electrode position (Fig. 11.4).

IMPORTANT Clip each electrode lead color to its

specified electrode position

8. Start the Biopac Science Lab software.

9. Choose lesson L11-React and click OK.

Connect the leads to the Subject, matching lead color to electrode position as shown above.

10. Type in a unique file name. No two people can have the same file name, so use a unique identifier, such as the subject’s nickname or student ID#.

11. Click OK. This ends the Set Up procedure.



B. Check

FAST TRACK Details

Check System – Complete this check for the first use of MP40 Feedback Cable only

1. Ignore all prompts and click Check MP40.

2. Click Devices.

3. Choose the audio input device to which the MP40 is connected and click Check System.

4. Set the dial to EMG (low).

5. Press and hold the Check pad.

6. Click when the light is flashing.

Run a system check to confirm the feedback cable is working.

MP40 Check

7. Set the dial to EMG (low).

8. Press and hold the Check pad.

9. Click when the light is flashing.

10. Wait for the MP40 Check to stop.

11. Subject puts on headphones and rests arm on table.

12. Let go of the Check pad.

13. Click Continue.

The MP40 Check procedure will last five seconds.

Subject should put on headphones and then rest forearm comfortably on a table top (or equivalent), palm down, posterior forearm up.

Signal Check

14. Click Check Signal. Subject lifts a finger when he/she hears the beep.

15. Click OK and wait for the Signal Check to stop.

16. Review the data.

At the end of the eight-second Signal Check recording, the screen should resemble Fig.11.5.

If correct, go to the Record section. If incorrect, click .

Fig. 11.5

If the recording check does not show a burst of activity for the finger lift, click Redo Signal Check.


C. Record

FAST TRACK Details

1. Prepare for the recording.

IMPORTANT DO NOT manually insert a marker in any

recording segment of this lesson. The software will insert markers as needed.

Watch the Help menu videos to prepare for the recording. You will record four segments, each requiring you to react by lifting your finger as soon as possible after hearing a click (stimulus):

a. Segments 1 and 2 present the stimuli at pseudo-random (1-10 second) intervals.

b. Segments 3 and 4 present the stimuli at fixed intervals (every 4 seconds).

Note It is hard to cheat on this lesson. The Biopac Science Lab software only looks for one response per stimulus, and it ignores responses that occur before the first stimulus, so it doesn’t help to lift your finger before you hear the first stimulus. If a reaction occurs before the stimulus or more than one second after the stimulus, it will not be used in the reaction time summary.

2. Prepare for the recording. Subject should be seated in a relaxed state, with headphones on, eyes closed. Subject should rest the hand on a flat surface so there is no muscle strain in the arm or hand.

SEGMENT 1 — Pseudo-random Trial 1

3. Click Record. When you click Record, a pseudo-random presentation trial will begin and an append marker labeled “pseudo-random” will automatically be inserted.

4. Subject should lift-and-return the finger as soon as possible after hearing a sound.

This pseudo-random presentation trial outputs a click at least one second apart but no more than ten seconds apart.

As soon as you hear each click through the headphone, lift-and-return your finger.

An event marker will automatically be inserted each time a stimulus click is output. Also, an upward pointing “pulse” will be displayed on the screen each time the finger is lifted.

The recording will suspend automatically after 10 clicks.

5. Review the data. If correct, go to Step 6.

After 10 clicks, the resulting graph should resemble Fig. 11.6. A pulse should be displayed after each event marker if the finger lift was detected correctly.

Fig. 11.6 Clicks indicated by pulse and marker

If incorrect, click Redo.

The data would be incorrect if: a) The recording did not capture a response pulse for each

click. Note If you miss more than two responses, you should



consider redoing the recording. b) The response pulse occurs before the event marker,

indicating the Subject reacted prematurely. c) The duration of the response pulse extends into the next

marker, indicating the Subject held the finger lift too long.

SEGMENT 2 — Pseudo-random Trial 2

6. Click Resume. When you click Resume, the recording will continue and an append marker labeled Pseudo-random (Trial 2) will be automatically inserted. You will record a second pseudo-random presentation trial.

7. Subject should lift-and-return finger as soon as possible after hearing a sound.





After 10 clicks, the resulting graph should resemble Fig. 11.6.

If incorrect, click Redo. Data would be incorrect for the same reasons listed in Step 5.

If data is incorrect, click Redo and repeat Steps 6-8.

SEGMENT 3 — Fixed Interval Trial 1

9. Click Resume. When you click Resume, the recording will continue and an append marker labeled Fixed-interval will be automatically inserted.

This fixed-interval presentation trial outputs a click every four seconds.

10. Subject should lift-and-return the finger as soon as possible after hearing a sound.





After 10 clicks have been output, the resulting graph should resemble Fig. 11.6 (but with fixed intervals between the clicks).

If incorrect, click Redo. Data would be incorrect for the same reasons listed in Step 5.

If data is incorrect, click Redo and repeat Steps 9-11.

SEGMENT 4 — Fixed Interval Trial 2

12. Click Resume. When you click Resume, the recording will continue and an append marker labeled Fixed-interval (Trial 2) will be automatically inserted. You will record a second fixed-interval presentation trial.

13. Subject should lift-and-return the finger at the sound of each click.




After 10 clicks, the resulting graph should resemble Fig. 11.6.


If incorrect, click Redo. Data would be incorrect for the same reasons listed in Step 5. If data is incorrect, click Redo and repeat Steps 12-14.

15. Optional: Click Resume to record additional segments.

Optional: You can record additional segments by clicking Resume instead of Done. A time marker will be inserted at the start of each added segment.

16. Click Done.

17. Click Yes.

18. Choose an option and click OK.

A pop-up window with options will appear. Click Yes (or No if you want to redo the last segment).

When you click Yes, the software will step through the data to record the reaction times to the journal, and then a dialog with options will be generated. Make your choice, and click OK.

If you choose Analyze current data file, go to the Analyze section for directions.

19. Unplug the headphones.

20. Remove the electrodes.

END OF RECORDING

Unplug the headphones, disconnect the lead clips, and peel off the electrodes.



V. ANALYZE

FAST TRACK Details

1. Enter the Review Saved Data mode and choose the correct file.

To review saved data, choose Analyze current data file from the Done dialog after recording data, or choose Review Saved Data from the Lessons menu and browse to the required file.

Fig. 11.7 Reaction times for pseudo-random trial

Note Following the press of the Done button in previous section, the program automatically calculated all 10 reaction times and average reaction times for each trial and placed them in the journal (Fig. 11.7). Use this journal information to fill in your data report.

2. Set up the measurement boxes as follows:

Channel Measurement

CH 1 Delta T

3. Select an area from the first event marker to the onset of the first response pulse and note the Delta T measurement in the Data Report.

A

The measurement boxes are above the marker region in the data window. Each measurement has three sections: channel number, measurement type, and result. The first two sections are pull-down menus that are activated when you click on them.

A brief description of these measurements follows.

Delta T: The Delta Time measurement is the difference in time between the end and beginning of the selected area, which is the duration of the selected area.

The signal starts to get larger at the onset of each response pulse.

Note The “selected area” is the area selected by the I-Beam tool (including the endpoints).

4. Set up your display window for optimal viewing of the first event marker and pulse of the first data segment (Fig. 11.8).

Fig. 11.8 First event marker and pulse segment

The following tools help you adjust the data window. Autoscale Horizontal Horizontal(Time) Scroll Bar Autoscale Waveforms Vertical (Amplitude) Scroll Bar Zoom Tool Zoom Previous

5. Look at the first reaction time result in the Journal and compare this to the Delta T measurement found above.

Analysis continues…

The two measurements should be approximately the same.


6. Repeat the steps above on other pulses until you are convinced that the Journal readings are accurate.

7. Transfer your data from the Journal to the Data Report.

B

This step may not be necessary if your Instructor allows you to print out your Journal and staple it to the Data Report.

8. Collect data from at least five other students in your class as needed to complete the Data Report.

C, D, E

9. Save or print the data file. You may save the data, save notes that are in the journal, or print the data file.

10. Exit the program.

11. Set the dial to Off.

END OF DATA ANALYSIS

END OF LESSON 11 Complete the Lesson 11 Data Report that follows.

Biopac Science Lab Page 11


Lesson 11 Reaction Time

DATA REPORT

Student’s Name:

Lab Section:

Date: I. Data and Calculations Subject Profile

Name Age Gender: Male / Female Height Dominant Arm: Right / Left Weight

Reaction Time A. Manually calculate the reaction time for the first click in Segment 1: Delta T = _____

Subject’s Results B. Summarize the subject’s results (copy from the software Journal)

Table 11.1

REACTION TIMES (ms) Pseudo Random Fixed Interval STIMULUS NUMBER

Segment 1 (1st trial)

Segment 2 (2nd trial)

Segment 3 (1st trial)

Segment 4 (2nd trial)

1 2 3 4 5 6 7 8 9 10

Mean

These are sample questions. You should amend, add, or delete questions to support your curriculum objectives.

Reaction Time vs Number of Presentations

C. Complete Table 11.2 with data from the first fixed-interval trial (data Segment 3) and calculate the mean for each presentation to determine if reaction times vary as each Subject progresses through the series of stimulus events.

Table 11.2 Comparison of Reaction Times

Student’s

Pseudo-random Trial 1 Data (Segment 1)

Fixed Interval Trial 1 Data (Segment 3)

Name Stimulus 1

Stimulus 5

Stimulus 10

Stimulus 1

Stimulus 5

Stimulus 10

1.

2.

3.

4.

5.

Calculate the Means:

Group Summary

D. Complete Table 11.3 with the mean for five students, and calculate the group mean.

Table 11.3

Class Data Pseudo-random trials Fixed-interval trials Student Means First Second First Second

1. 2. 3. 4. 5. Calculate the Group Means:


Variance and Standard Deviation E. Calculate the variance and standard deviation for five students with data from Segment 2: Pseudo-

random Trial 2 (Table 11.4) and from Segment 4: Fixed Interval Trial 2 (Table 11.5).

datastudent all of Sum

students) allfor (constant mean Group X

studenteach for imereaction tmean Xjstudents ofnumber n

Variance =Deviation Standard

)x - (x1n

1 = Variance

n

1j

2n

1 = jj

∑

∑

=

=

=

==

−

Where

Table 11.4 Segment 2: Pseudo-random Trial 2 Data

ENTER ENTER CALCULATE CALCULATE Mean Reaction

time for Student

Group Mean

Deviation

Deviation2 Student (X )j (X) (X - X)j

(X - X)j2

1 2 3 4 5

Sum the data for all students =

=

Variance (σ2) = Multiply by

=

Standard Deviation = Take the square root of the variance =

=

Table 11.5 Segment 4: Fixed Interval Trial 2 Data

ENTER ENTER CALCULATE CALCULATE Mean Reaction

time for Student

Group Mean

Deviation

Deviation2 Student (X )j (X) (X - X)j

(X - X)j2

1 2 3 4 5

Sum the data for all students =

=

Variance (σ2) = Multiply by 0.25 =

=

Standard Deviation = Square root of Variance =

=

II. Questions F. Describe the changes that occurred in the mean reaction time between the 1st and 10th stimuli

presentation:

For Segment 1:

For Segment 2:

Which segment showed the greatest change in mean reaction time? Segment 1 Segment 2 G. Refer to Table 11.2 and Table 11.3:

Estimate the minimal reaction time when reaction time becomes constant: sec

What physiological processes occur between stimuli presentation and the motor response?

H. Refer to Table 11.2:

Which presentation schedule had the lowest group mean? Pseudo-random Fixed-interval I. Refer to Table 11.2 and Table 11.3:

Which of the presentation schedules seems to have less variation (lower variance and lower standard deviation)? Pseudo-random Fixed-interval

J. Refer to Table 11.2 and Table 11.3:

State a plausible relationship between the difficulty of a task and the reaction time statistics: mean, variance, and standard deviation.

K. What differences would you predict in reaction times and learning between your right and left hands?

End of Biopac Science Lab Lesson 11 Data Report

Biopac Science Lab Page 15


VI. ACTIVE LEARNING LAB

Design a new experiment to test or verify the scientific principle(s) you learned in the Biopac Science Lab recording and analysis segments.

For this lesson, you might examine how reaction times vary with the dominant and non-dominant arms, or repeat additional trials to see if reaction times improve. You could also introduce other elements, such as asking the subject to read aloud or listen to music, and examine their influence on reaction times.

Design Your Experiment

Use a separate sheet to detail your experiment design, and be sure to address these main points:

A. Hypothesis

Describe the scientific principle to be tested or verified.

B. Materials

List the materials will you use to complete your investigation.

C. Method

Describe the experimental procedure—be sure to number each step to make it easy to follow during recording.

See the Set Up section or Help > About Electrodes for electrode placement guidelines.

Run Your Experiment

D. Setup

Set up the equipment and prepare the subject for your experiment.

E. Recording

Use the Record, Resume, and Suspend buttons in the Biopac Science Lab program to record as many segments as necessary for your experiment.

Click on Done when you have completed all of the segments required for your experiment.

Analyze Your Experiment

F. Set measurements relevant to your experiment and record the results in a Data Report.

Documents

Physiology Lessons Lesson 11 Reaction Time Fixed & Pseudo