Cognition Laboratory Experiments

John H. Krantz, Hanover College, krantzj@hanover.edu

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Hanover College
Psychology Department

Instructions for the
Dual Task Experiment

In this experiment, you can experience a dual task situation.  In many real world situations people are required to monitor or pay attention to more than one task at a time.  For example, while driving you have to both monitor your position on the road and monitor your speed.  Psychologists study our ability to do two things at once in the dual task experiments.  In this version of a dual task experiment, there is a primary tracking task where you will try to keep a dot inside of a box, sort of like following the road.  During this tracking task, letters appear and if a target letter (X) appears you have to respond to it by clicking the mouse.  You can manipulate the features of both the primary and secondary tasks to see how they impact your ability to do both successfully. 

When you click on the link below, you will be presented with the experiment setup screen.  On this screen will be the variables you can set to define your condition.  Here is a list of the variables and their settings

Variable Settings
Number of Trials The number of trials in the conditions from 5 to 100
Number of Practice Trials The number of practice trials, during which the participant will practice the primary tracking task only.  From 0 to 50.
Practice the Secondary Task Click to allow the secondary task to occur during the practice trials.  Currently no data from the secondary task is collected.
Duration of the Trial The length of each trial in seconds.  From 10 to 120.
  Variables for the primary tracking task.
Range angle varies The range that the direction of the motion of the dot to be tracked can change with each update from 0 to 360.  The smaller the angle variation, the more direct the movement of the dot and thus easier to follow.  The larger the angle variation the more random the movement of the dot.
Speed of Dot How fast the dot moves (pixels per update, from 1 to 50)
Size of dot to track The diameter of the dot (in pixels, from 1 to 20).
Size of target box The size of the target box that you must keep the dot in during tracking (in pixels, from 2 to 200).
Give Tracking Feedback Use color to indicate tracking performance.  Cyan means dot is in the box, yellow means the dot is out but not at a great distance, red means the dot is far from the box.
  Variables for the secondary letter detection task.  Only those variables that refer to a given type of secondary task will be visible.
  Generic Secondary Task Parameters
Secondary Task Stimulus Type Select what stimuli are going to be used for the secondary task.  Either letters or single frequency tones.
Percentage of targets The probability that each letter presented would be a target (from 0.01 to 1.0).
Duration of stimulus How long the letter is presented (from 25 to 1000 msec)
Average time between Stimuli The average period of time after the end of one stimuli to the presentation of the next stimulus (from 25 to 4000 msec).
Variation in ISI The range that the time between letters can vary (from 0 to 1.0 proportion of the average time between letters).
Response window The time after the presentation of the target letter, during with the participant must make a response for it to be counted as a response to the target and not a mistaken response (from 250 to 3000 msec).
  Next are letter secondary task related variables
Set the targets and distracters These button allow the setting of the strings used for the targets and distracters.  Clicking on either button will open a window where the number of items can be set by entering a text window at the top.  Then the items can be placed in each other other text fields on the window.  Clicking the done button at the bottom of the window completes the setting of the items.
Font Size The size of the letters that are presented (from 12 to 64 point)
Rel X Pos The relative position in the x-axis of the letter on the screen from the left side.  (0.1 is one-tenth the way across the screen to 0.9 or nine-tenth the way across the screen).
Rel Y Pos The same as above but in the y axis starting with the top of the screen.
  Next are sound secondary task related variables
Frequency of Target Sets the frequency of the tone that will be the target (100 to 5000 Hz).  The button below this slide will place a sample of the tone.  Remember that the stimulus duration variable influences how it will sound.
Frequency of Nontarget Same as above but for nontarget sound.

After you have finished making your settings, press the Done button at the bottom of the screen.  The Dual Task experiment screen will then be presented.  A start bar will be at the top of the screen at every trial and instructions for that trial will be in the center of the screen.  The instructions will indicate what the target stimuli will be.  If text is used, the targets will be printed with the instructions.  If sound stimuli are used, buttons at the bottom of the screen will play both the target and nontarget stimuli.  Practice trials, if any will occur first.

Press the space bar to begin the trial.  To track simply move the move around the screen and the box will follow.  If you use feedback, the box will be cyan when the dot is in the rectangle and no tracking error will be recorded.  At the end of a practice trial, your total tracking error, in pixels, during the trial will be given to you.  To respond to the targets, press the left mouse button.

The actual experimental trials are the same except that during the tracking, the secondary task stimuli are presented.  If the target stimulus(i) is presented on the screen, click the mouse button to indicate that you have perceived that a target stimulus has been presented.  At the end of these trials, no feedback is given.

At the end of the experiment your results will be presented.  You will be given your average tracking error, the average proportion of targets that you responded to, and the relative number of nontargets responses you make relative to the number of targets presented.  You can get your responses for each trial by clicking on the Trial Data button at the bottom of the screen.

Click here to start the experiment.

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