EXPERIMENT DESIGN: Stage 5: Add Practice Block [37332]

There are four steps involved in adding a practice block, as shown in the following table:

 

Stage 5: Add Practice Block

1) Define Practice Block

2) Add the Practice Block Variable

3) Define the Practice Performance Criterion

4) Verify

 

Stage 5, Step 1: Define Practice Block

From the participant’s perspective, the practice block is just like the “real” experimental block; the same events happen on each trial and the same exemplars are sampled. The only differences between the practice and experimental trials are:

• The practice block of trials needs to be identifiable as such, so that the practice data is not included in the data analysis. This requires a new block independent variable, which is set up in Step 2 below.
• The participant’s overall accuracy at the conclusion of the practice trials needs to be checked to see if the participant has met the performance criterion.
• If the participant has not met the performance criterion, then the practice block is presented again. If the participant has met the performance criterion, then the experimental trials are presented.

Stage 5, Step 2: Add the Practice Block Variable
In order to easily analyze the practice data separately from the main data, a variable can be added that codes the information as practice or experimental trials. The new variable can be named “PracticeMode”. There are many different ways that practice trials can be identified; in this case, we will identify all of the trials in the practice block as “Practice” and all of the trials in the experimental block as “Real”:

 

New Independent Variable
Block condition	PracticeMode
Practice trials	Practice
Experimental trials	Real

 

Stage 5, Step 3: Define the Practice Performance Criterion
It is good practice to check the participant’s performance after completing some practice trials to ensure that the participant has understood the task and is performing at a level that will enable meaningful data analysis (e.g., reaction time analysis is filtered on correct responses only, so reasonable numbers of trials need to be included for each participant).

 

Add InLine to check accuracy
To enter the code script to check accuracy, add an InLine object to the SessionProc following the practice trials. The example script below requires participants to perform at greater than 80%; otherwise, the practice block is presented again.

 

If Feedback.ACCStats.Mean > .80 Then
 EndPrac.Text = "Get ready for the real trials"
Else
 EndPrac.Text = "You did not achieve the accuracy. You must repeat practice."
 EndPrac.Run
 GoTo Label1
End If

 

The script above examines the value of Feedback.ACCStats.Mean (calculated automatically by the Feedback object) to determine if the participant achieved 80% accuracy. If this value is greater than 80%, the practice trials terminate and the experiment continues with the real trials (i.e., the next object in the experiment). If the participant did not achieve greater than 80% accuracy for the practice trials, the practice trials are repeated using the Goto command to jump to Label1. Using this method, the practice trials will continue until the Criterion for continuation is met. The Feedback.ACCStats.Reset command is used to reset the Feedback accuracy statistics to zero before rerunning practice. The InLine is also setting the text to display using an E-Object called EndPrac.

Place a Label prior to the Practice Trials

The example above refers to a Label named Label1. Label1 should exist on the SessionProc just prior to the List object that is running the practice trials. Label1 marks the location in the SessionProc to which the Goto command refers. If the required accuracy level is not achieved during the practice trials, the execution of the experiment will jump back to Label1 and rerun the practice trials.

 

Refer to E-STUDIO: Label Object [22712] for more information on the Label object.

 

Add an E-Object to show whether Accuracy Criteria is met
Lastly, the example script above mentions an E-Object named "EndPrac". It is important to inform the participant whether they have met the accuracy criterion. We do this by adding the EndPrac object to display the text determined by the preceding CheckAccuracy Inline object. The text for this object to display will be assigned at runtime via the InLine script shown above. Therefore, no text needs to be entered for this object. The EndPrac object is not necessary for the process of repeating the practice trials, but helps to make the experiment execution more understandable to the participant.

 

Stage 5, Step 4: Verify
As always, at the end of an incremental design stage, you should be able to envision the displays that the participant would see and anticipate how to analyze the data.  The procedure was expanded to present a practice block, and to inform the participant about their practice block performance.

The data analysis will change due to the addtion of the practice trials. The addition of a new block independent variable named “PracticeMode” results in a new column of data added to the expected data file structure. The new variable will need to be used in the data analysis to exclude all practice trials from real trial analysis.

 

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