Lexical decision task

This tutorial will walk you through creation of a full lexical decision task experiment (Meyer & Schvaneveldt, 1971) [1]. This example will be based on Experiment 1, where word pairs are presented with a limited time period to respond. The task requires participants to identify whether each word pair contains a non-word. At the end of each trial, participants are given feedback as to the correctness of their response. A timeout (no response within the given time) also equates to incorrect. Word pairs are associated with one of the following levels:

• Related: word pair contains real words that have some semantic relationship.
• Non-word: word pair contains at least one non-word.
• Unrelated: word pair contains real words that have no semantic relationship.

Tip: Throughout the tutorial there will be links to other documentation to explain concepts in detail. If you follow a link you can return to this tutorial by hitting the back button in your browser. Alternatively, you can right-click a link and open it in a new tab.

Objectives

At the end of this tutorial you will have covered the following concepts:

• creating a study in Psychstudio.
• creating a stimulus set.
• importing stimuli and auto-populating factors and levels.
• designing trials on the trials timeline.
• designing visuals in the trials screen.
• adding logic to trials using rules.
• navigation of the study tree and an introduction to the experiment flow it represents.
• introduction to the stimulus manager.

Design

Simple one-factor, three-level experiment using randomly selected stimuli.

Method

• Create a new study

  1. Create a new study, call it Lexical decision task and choose New as the creation option.

• Create the trials timeline

  1. Navigate to the Study sequence by clicking on it in the study tree.
  2. Create a new trial block by clicking New item and selecting Trial block, choosing New as the creation option and naming it Trial block.
  3. Navigate to Trial block by clicking on its name in the table or in the study tree.
  4. Create a new trials construct by clicking New item and selecting Trials, choosing New as the creation option and naming it Trials.
  5. Navigate to Trials by clicking on its name in the table or in the study tree to arrive at the trials timeline.
  6. Create a new stimulus set for the trials to operate on by clicking Stimulus set: nil and selecting Create new set... and name it Stimuli, then click Save.

• Create stimuli for the study

  1. Navigate to the stimulus manager by clicking the Stimuli tab in the study tab bar.
  2. Click Components in the stimulus set tree and add a new group called word pairs with the component group type Discrete and the component type Text.
  3. Navigate to the word pairs group by clicking on its name in the table or in the stimulus set tree.

  4. Create a CSV file containing your word pairs, and their associated factors and levels then import the CSV file. For convenience, you can download one I prepared earlier. The CSV file should look like this (Figure 1).

     

     Figure 1. CSV file of word pairs with associated factors and levels (Lexical decision task)

• Add items to the trials timeline

  It's time to add items to our trials timeline.
  1. Click on Study in the study tab bar to go to the study screen. Notice the factors and levels from our CSV file have automatically populated the factors table.
  2. Navigate to Trials by clicking on it in the study tree.
  3. Add a fixation to the timeline by clicking New item and selecting Fixation, choosing New and naming it fixation.
  4. Click on the fixation item in the trials timeline to enter edit mode, set the Timeout (ms) to 250 and set the fixation Type to Cross (vertical).
  5. Add a New Interstimulus interval called ISI.
  6. Click on ISI and set the Start time (ms) to 250 and Timeout (ms) to 200.
  7. Add a stimulus component by clicking New item, selecting Stimulus component and choosing word pairs (this is the stimulus component we created earlier).
  8. Click on word pairs and set the Start time (ms) to 450 and Timeout (ms) to 1000.
  9. Click New item and add a keyboard response by selecting Response - keyboard, choosing New and naming it keys.
  10. Click on keys and add the following using the Add key button:
      • Key: f, Value: pair only contains real words
      • Key: j, Value: pair contains a non-word

      Set Start time (ms) to 450 and Timeout (ms) to 1000.

      Hit Save in the bottom right corner when you've finished.

  11. Click New item and add a Feedback item by selecting Feedback, choosing New and naming it feedback.
  12. Click on feedback and set the Timeout (ms) to 250.

  We have now completed our trials timeline and it should look something like this (Figure 2).

  

  Figure 2. Trials timeline (Lexical decision task)

• Create the trials screen

  1. Navigate to the trials screen by clicking Screen in the trials tab bar.
  2. Add fixation to the screen by hovering the mouse over the top of the grid and selecting the cell and then selecting fixation from the Insert item list.
  3. Select the 450ms interval on the screen timeline (Figure 3) and add word pairs to the screen using the same method you used to add fixation in step 2.
  4. Select the Feedback interval on the screen timeline (Figure 3) and add feedback to the screen using the same method you used to add fixation in step 2.

  We have now finished building our trials screen. You can preview your work so far by clicking Preview study at the far right-hand end of the study tab bar.

  

  Figure 3. Screen timeline for the lexical decision task

• Create the trials logic

  1. Navigate to trials logic by clicking Logic in the trials tab bar.
  2. Add the rules shown in (Figure 4).

  

  Figure 4. Trials logic for the lexical decision task

  We have now finished building our trials logic, and with that, our experiment design is complete.

• Finishing touches

  Although our experiment design is complete, it's not very friendly, so let's fix that.

  1. Navigate to Trial block using the study tree and add new instructions, name it Instructions and choose New as the creation option.
  2. Drag Instructions to the top position in the trial block table to make it appear before Trials.

  3. Add some introductory text (Figure 5).

     

     Figure 5. Trial instructions (Lexical decision task)

     Note: we could have created Instructions in the study sequence above Trial block but bundling Instructions within a trial block provides the following advantages:

     • instructions are moved along with the trials when the trial block is moved.
     • instructions remain with the trial block when that block is part of a randomized block design.
     • when added to a trial block (appearing before trials in the trial block table), we get a keyboard legend added to our instructions which is essential when key randomization is utilized.

  4. Add a keyboard response to your instructions by clicking New response, selecting Response - keyboard, New as the creation option and name it key.
  5. Click Edit on key and add a new key. Press the Space bar to add the space key, set the value to anything you like (e.g. next), then hit Add to add the key and then hit Save to exit edit mode.
  6. Navigate to Study sequence.
  7. We are now going to add some instructions in the form of a thankyou message but this time we'll save ourselves some work by copying some instructions we created earlier. Click New item, select Instructions, select Copy as the creation option, select Instructions (the instructions we created in earlier in Trial block) and name it Thankyou message.
  8. Navigate to Thankyou message and change the text to a lovely thankyou message and change the space bar text to something like Press the space bar to exit. Note: The last screen in your study must include a buttons response or a keyboard response to end the study. Set the response Event to Go to next study item or trial.

Congratulations

You now have a fully functional experiment with random stimulus selection and per-trial participant feedback. Hit Preview study and try it out! To activate the study and allow participants to take part, hit the Distribution tab in the study tab bar. To download results, hit the Results tab in the study tab bar.

References

1. Meyer, D., Schvaneveldt, R. (1971). Facilitation in recognizing pairs of words: Evidence of a dependence between retrieval operations. Journal of Experimental Psychology. 90(2) 227–234. doi: 10.1037/h0031564