Loops and Lists

There are two files on GitLab called list_block_1.csv and list_block_2.csv. Please download and save these in the experiment folder you created at the beginning of this guide.

In the final study, participants will see 200 items in total, split evenly across 2 blocks of 100 items. In the first block, a sentence must be responded to as sensible or nonsense using the W or S keys. In the next block, we will change the keys around to ensure that any effects we find aren’t due to preferences for pressing one key over another. Across the files, we also vary whether a transfer sentence indicates transfer towards or away from the partipant. So, for any given transfer sentence it can either have W or S as a sensible response and transfer towards or away from the participant. This leaves us with 4 versions of the sentences. We finally want to control whether some participants see a given sentence in the first or second block, hence the two files.

We thus randomly assign participants to one of these 4 versions, or lists to ensure that we have properly counterbalanced the study.

These contain the trial information:

• list: Which list of items we will use to display sentences in the main phase of the study.

• block: Which block of the study this data belongs to. There are two blocks in total. In the second block we reverse the buttons used to indicate a correct and incorrect response for counterbalancing.

• phase: This indicates which phase of the data the item belongs to. This is ‘prac’ for the practice phase and ‘exp’ for the main, experimental phase of the study.

• item: The number for the item corresponding to the sentence for each trial.

• sensibility: Whether the sentence makes sense (sensible) or not (nonsense).

• concreteness: whether the sentence describes a concrete or abstract scenario. For example, a concrete sentence might be ‘You dealt the cards to Chantelle’, while abstract might be ‘Umaira gave you another chance.’ If the sentence makes no sense, this is NA.

• type: Whether the sentence describes transfer of something from one character to another (tranfer) or not (no_transfer). If the sentence is nonsense, this is NA.

• direction: If a sentence describes transfer, does the described transfer occur from a character to you (towards) or from you to the character (away). If no transfer occurs or the sentence is nonsense, this is NA. 

• sentence: The sentence to be displayed on screen to participants. 

• correct_response: The correct key on the keyboard that participants should press to respond if the sentence makes sense or not. For some participants the first block will make sensible items a W and nonsense items an S. For others this will be reversed.

We currently only have the trial list for the experimental blocks. We will now create our own practice trial list. To do this create a .csv file in Excel, Google Sheets, or any speadsheet document you’re comfortable with and call this prac_trials. Next, create 10 columns with the same names as those in the experimental trials (in bold above).

In the sentence column, you can add the following sentences in order.

• You gave the news article to Ben.

• You read the email with Ian.

• Stephen sent you the alpha.

• Joe drank the danger with you.

These will be the sentences participants will see on screen across four practice trials.

Fill out the remaining details here using the information in the screenshot below.

21 - The information to add to the prac_trials.csv file.

Now that we have created the practice trial, we need to add a loop to the experiment. We do this by clicking Insert Loop then inserting where we want it to begin and end on the timeline. Here, we want it just before the Fixation_Cross and right after the Sentence_Screen components.

22 - Inserting a loop.

Rename the loop to prac_trials. We will then set some important information for the loop. First, in the popup menu set the nReps to 1, then click the folder icon next to the conditions section. Select your prac_trials.csv file and then click OK.

We have now loaded our trial information for the practice section into PsychoPy and through nReps ensured that people only see this entire table of trials once.

23 - Selecting the variables for the practice trial loop.

As of right now, nothing different will shown on the experiment, other than it looping four times. This is because we have not told PsychoPy which parts of the experiments need to be updated on every iteration of the loop.

To make the sentences update and the correct response vary for any given trial we need to set our variables.

First, to update the sentences we need to go back to the trial screen and into the text component. We will then delete Test Sentence from the Text box and write $sentence. We will then change the text from constant to set every repeat. (This option is a dropdown menu right next to the Text option in the popup.)

The dollar sign signify that PsychoPy should be looking for a variable named sentence (which is in the excel file). Setting the sentence to set on every repeat means that for every iteration of the loop PsychoPy will select a different line in the excel file to read from.

24 - Updating our sentences in the practice loop.

To update the correct responses for each trial we then need to click on the key_sentence component and in the popup menu go to the Data tab. From here, tick the Store correct box, and in the Correct answer box enter $correct_response. This allows the correct response to vary for each trial in the same way the sentence varies; PsychoPy looks in the correct_response column in the prac_trials.csv file and pulls out the entry for a given trial as the correct key participants should choose.

25 - Updating the correct answer in the practice loop.

We should now run the experiment to test that the sentences are updating every loop. Do this by pressing play in the same way as we did earlier.

After the practice loop we want to show the instructions again. Our first step is to copy the Instruction_Screen routine. First click on the Instruction_Screen routine, then select the Experiment menu at the top of PsychoPy, and click Copy Routine. Then click Paste Routine. You will be prompted to rename the screen. Please rename it to Experiment_Instructions. Then go to the Experiment tab again, click Insert Routine in Flow, click on Insert Routine in the Flow panel, and place it at the end of the timeline outside the prac_trials loop.

26 - Inserting the new instructions in the timeline.

Now we need to add an experimental loop. Click on Insert Routine in the Flow tab. Then click on Fixation_Cross and add it to the timeline after the Experiment_Instructions routine. Do the same for the Sentence_Screen.

Next, insert a loop for the experimental trials. In the Flow tab click Insert Loop. Set this to begin before the Fixation_Cross and to end after the Sentence_Screen. Name this loop to exp_trials, and then set the nReps to 1.

27 - Inserting the main experiment loop.

Because we have two blocks we want to show, we’d like to repeat showing the instructions along with the experimental block loop. To do this, add another loop around the Experiment_Instructions routine and the exp_trial loop by clicking Insert Loop. Name this loop block_loop and set the nReps to 1.

This will ensure that for each block of the study, participants will see the instructions (which varies across blocks). Within each block participants will see a fixation cross and a sentence screen on every trial.

28 - Inserting the block loop.

No we have the general flow of the experimental blocks of the study, we will have to let PsychoPy know where to access the trial information for each block.

We will now create a conditions file that will update which file the loop will use on each iteration. Create a .csv file as before and make two columns with the following titles and contents:

1. cond_file: this has the entries list_block_1.csv and list_block_2.csv. This will change which conditions file each block loop is reading from.

2. block: this has the entries 1 and 2. This column keeps track of which block has been picked so we can use this in assigning the correct instructions for a given block.

Save the .csv file as cond_files.csv.

29 - Creating cond_files.csv for the block_loop.

Click on the block_loop label in the timeline. You should see the block_loop Properties popup window. Next to the Conditions line, select the folder icon and choose the cond_files.csv and loop type to be sequential . Click OK.

30 - Setting the block loop properties.

Next, click on the exp_trials loop label in the timeline. In the Conditions section type $cond_file.

Now, the block_loop randomly selects the order of the blocks, and thus which item list should be selected for a given block. By choosing the conditions file to be decided by whatever the block_loop picked, we allow the exp_trials loop to randomly select items only from the correct .csv file for any given block.

Now, our blocks are randomly ordered for any given participant: some see the item list named ‘list_block_1.csv’ first, while others see ‘list_block_2.csv’ first. Crucially, the presentation of trials within these blocks is also randomly ordered.

31 - Setting the exp_trials to use dynamic updating of the item list.

Custom Code

Remember that each file of items (i.e. list_block_1.csv and list_block_2.csv) has separate lists within it. These lists essentially have the same items within them, only with different versions which reflect the four combinations of direction of movement in the sentence (i.e. towards or away from the participant) and the button participants use to select a correct response (i.e. W or S). (Look at list_block1.csv and compare item 1 in list 1 and list 3 to see how this works.)

We don’t want to show participants the same item 4 times. Instead, want them to only see 1 version of each item. So we need some custom Python code to (1) assign participants to a given list, and (2) subset the list of items to only those from the participant’s list.

We will focus on how to randomly assign a list in Qualtrics later. For now we will manually select which list to select using the expInfo options within the experiment settings. Access the experiment settings by clicking the big cog symbol at the top of the PsychoPy interface. You will see popup menu for the settings. In the Experiment info row, click the + symbol to create a new data field. In the field column, name the data field list_select. Leave the Default value to to blank. Click OK. This now makes the experiment ask which list to use at the beginning of the study.

32 - Accessing the experiment settings and creating the list_select field.

Now we will add a custom code component. First, click on the Experiment_Instructions tab. Then, in the Custom field within the Components menu, choose Code. You will see a popup window.

33 - Adding the custom code component.

34 - Since the study now asks us which list to use at the beginning of the study, we can use this input to filter our items down to only those for the correct list of items. That’s what this code does. It checks which list is selected and then keeps rows only for the items associated with that list.

In the popup window, click on the Begin Experiment tab. Paste in the following code and then click OK.

list_select = expInfo['list_select']

if list_select == "1":
    row_select = "0:100"
elif list_select == "2":
    row_select = "101:200"
elif list_select == "3":
    row_select = "201:300"
elif list_select == "4":
    row_select = "301:400"

35 - Adding the code to the Begin Experiment tab.

Right click the code component and select move to top. This will make the code run at the beginning of the routine before participants see anything on screen.

36 - Reordering the code component.

Now that we have determined which rows we would like to keep from the item list for each participant, we need to apply the subsetting of the list within the experimental trials loop.

Click on the exp_trials loop and in the exp_trials Properties popup window type $row_select in the Selected rows box. This adds a variable to the loop which allows it to filter the list of items down to only those in a given list.

37 - Applying the list filtering to each conditions file.

Next we need to add some meaningful instructions to the experiment. We will start with the practice instructions. We want our instructions to explain what the participant is expected to do. Select the Instruction_Screen routine and click on the text component there. Replace the text in the Text box with the following:

Read the sentence and decide if it is sensible.

Press W for Yes

Press S for No

Press Space when you are ready to start and to progress through each screen.

38 - Adding instructions to the practice trials.

Since the experiment has one key for a sensible answer in the first block (e.g. W), and then reverses the key for the second block (e.g. S), we need to dynamically update our instructions for each block.

These answers will be based on the correct_response column in the conditions files list_block_1 and list_block_2.

1. For block 1:

   1. List 1 and 2 are W for Yes and S for No

   2. List 3 and 4 for W for No and S for Yes

2. For block 2:

   1. List 1 and 2 are W for No and S for Yes

   2. List 3 and 4 for W for Yes and S for No

We achieve this by create another conditional statement that checks both which list we are using and which block we are in and then assigns new instructions based on this.

Click the Experiment_Instructions routine then click on the code component. In the Begin Experiment tab paste the following under your existing code:

block_count = 1 # starts block at count 1 for the first block
instruction_text = "" # blank instruction string

Make sure to copy and paste the code into the correct tabs as we will want to create a variable before the routine starts and execute code at the beginning and end of the routine. If the new code is indented from the side of the window then your code won’t work.

Your final code in this section should look like this:

list_select = expInfo['list_select']

if list_select == "1":
    row_select = "0:100"
elif list_select == "2":
    row_select = "101:200"
elif list_select == "3":
    row_select = "201:300"
elif list_select == "4":
    row_select = "301:400"

block_count = 1 #starts block at count 1 for the first block
instruction_text = "" #blank instruction string

39 - The final code in the Experiment_Instructions component.

Next, we’ll allow the experiment to update the instructions within each block. Here, we ask the program to check which list of items has been selected at the start of the experiment, and which block participants are in. We then update the instruction text to the relevant instructions for the participant. Note that in the text that we input we use “\n” to create a new line.

In the Begin Routine tab of the code properties paste in the following code:

(Note: This code could be easily improved by printing the string using variables to change out the relevatn parts. Since this is for those new to Python it is kept intentionally verbose.)

# checks which list was selected and what block it is
if list_select == "1" and block_count == 1:
    instruction_text = "Read the sentence and decide if it is sensible\nPress W for Yes\nPress S for Non\nPress space bar to start the experiment and progress through the screens"
elif list_select == "2" and block_count == 1:
    instruction_text = "Read the sentence and decide if it is sensible\nPress W for Yes\nPress S for Non\nPress space bar to start the experiment and progress through the screens"
elif list_select == "3" and block_count == 1:
    instruction_text = "Read the sentence and decide if it is sensible\nPress S for Yes\nPress W for Non\nPress space bar to start the experiment and progress through the screens"
elif list_select == "4" and block_count == 1:
    instruction_text = "Read the sentence and decide if it is sensible\nPress S for Yes\nPress W for Non\nPress space bar to start the experiment and progress through the screens"
elif list_select == "3" and block_count == 2:
    instruction_text = "Instructions have changed\nPlease Read carefullynnRead the sentence and decide if it is sensible\nPress W for Yes\nPress S for Non\nPress space bar to start the experiment and progress through the screens"
elif list_select == "4" and block_count == 2:
    instruction_text = "Instructions have changed\nPlease Read carefullynnRead the sentence and decide if it is sensible\nPress W for Yes\nPress S for Non\nPress space bar to start the experiment and progress through the screens"
elif list_select == "1" and block_count == 2:
    instruction_text = "Instructions have changed\nPlease Read carefullynnRead the sentence and decide if it is sensible\nPress S for Yes\nPress W for Non\nPress space bar to start the experiment and progress through the screens"
elif list_select == "2" and block_count == 2:
    instruction_text = "Instructions have changed\nPlease Read carefullynnRead the sentence and decide if it is sensible\nPress S for Yes\nPress W for Non\nPress space bar to start the experiment and progress through the screens"

40 - Adding instructions to the Begin Routine tab of the code property.

Next, we need to make sure we have a variable that keeps track of the block number. This is needed so we can give participants the correct instructions for their list in the first block, and then change the instructions in the second block. We’ll make a variable called block_count that is set to 1 and that increments its value by 1 after the end of each block.

In the End Routine tab of the code property paste the following code:

block_count += 1

41 - Adding code that increments the block number by 1 at the end of each block.

Finally, we will change the text in the Experimental section of our study. In the Experiment_Instructions routine click the text component. Change the text in the text block to the following code:

$instruction_text

Next, on the dropdown menu to the right of the text block change the selection from constant to set every repeat. This means that the experiment will update the instructions for every iteration of the block loop.

42 - Setting the experiment instructions text to dynamically update depending on list and block number.

Now run through the experiment to see if everything is working alright.

Once you can confirm it is working fine, we will get the experiment to work online. To run an PsychoPy experiment online, we need a Pavlovia account (go to https://pavlovia.org/ and create an account with your student email. If you’re registered at a University with a site license (such as at the University of Sunderland) you should register using your student email. Pavlovia will automatically apply the University site license to your account so you don’t need to pay for data collection.

Before we can get our experiment working on the Pavlovia servers, we need to make sure PsychoPy knows to send all the conditions files to the servers. When we select our files on the computer from within subfolders sometimes they aren’t automatically uploaded, so we need to do this manually. We do this by clicking on the settings icon (the cog) at the top of the PsychoPy interface and going to the Online tab. Click the + symbol to the right of the Additional Resources box and select the files list_block_1.csv and list_block_2.csv. Click OK and save your work.

43 - Adding the conditions files to the additional resources before deploying the study online.

We are now ready to get the experiment working online. Click the internet symbol (webbed globe) that has the sync button next to it (the second in the selection). A popup window will ask you to sign in to Pavlovia. Do so and another window will state “This file doesn’t belong to any existing project.” Click the Create a project button.

Name the project PSY260_Experiment. Write a description for the project to help you remember what this is about. When you’re done, click Create project on Pavlovia.

A new window will ask you to Commit your changes for the study.

This is a concept from version control systems. Basically, you put your files in a repository that is synced online. When you make changes to your study/programming code, you can save then and then commit them to the project. Once these changes are pushed online to the remote version of the repository your project is updated. Crucially, you will always have access to previous versions of your work. No more creating several versions of your work with obscure names!

Write a summary of your changes. In this case you could just make this “first commit”. Any further commits should describe what you’ve changed. Add details to any commits as and when you please to help you remember what changed.

44 - Syncing your study with Pavlovia. Creating a project, providing a description, and then commiting your study.

Now go to https://pavlovia.org/ and set the experiment to pilot. You can use this to check that your experiment runs in the way you expect. This is an important step before you release it for other people to take part.

To do this go to the Dashboard, then Experiments and select the experiment you have just created.

45 - Selecting your experiment in the Dashboard.

One your study page loads select the Piloting option for the study. This will make the study active for one hour at a specific link so you can test it works properly.

Click the button that says Pilot to run your study in the browser and test it out. Make sure it behaves how you expect before you progress.

46 - Piloting your study.

If you need to change your study, do so and then sync the changes with Pavlovia again by clicking the web sync button and committing your changes.