Configuring Test Parameters

Quick Summary: Customize test behavior by adjusting parameters like timing, trial counts, difficulty, and more through the web interface.

What You'll Learn

• How to access the parameter configuration interface
• Understanding different parameter types
• Common configuration tasks
• Best practices for parameter adjustment
• Troubleshooting configuration issues

Overview

Every PEBL test includes configurable parameters that control its behavior. Rather than editing test code, you can adjust these settings through a simple web interface. Each study can have different parameter configurations for the same test, allowing you to run multiple variants of experiments.

How Parameters Work

Parameters Are Test-Specific

Each PEBL test defines its own set of parameters that are embedded within the test code itself. There are no universal parameters that apply to all tests. This means:

• The Corsi Block Test has parameters like maxspan (maximum sequence length) and dotsize (size of blocks)
• The Stroop Task has different parameters like numtrials (number of trials) and isi (inter-stimulus interval)
• A parameter that exists in one test may not exist in another test, even if they seem similar

Why it matters: When you configure parameters, you're only changing settings for that specific test. You cannot create "global" parameter settings that apply to multiple different tests.

The Default Parameter Set

When you first add a test to your study, it uses default parameters defined by the test developer. These defaults:

• Are chosen to work well for typical research scenarios
• Are stored in each test's schema file (.pbl.schema.json)
• Are automatically applied when you run a test without custom configuration
• Can be viewed and modified through the Configure interface

You don't need to configure parameters - the defaults are perfectly fine for most studies. Only adjust parameters when you have specific research requirements.

Multiple Parameter Sets (Named Configurations)

You can create multiple named parameter configurations for the same test within a study. This is useful when you want to run different variants of the same test.

Example use cases:

• Easy vs. Hard difficulty versions of the same test
• Short (10 trials) vs. Long (100 trials) versions
• Different timing parameters for different age groups
• Multiple rounds of the same test within a test chain, but with different conditions.

How it works:

1. When you first configure a test, you're editing the default parameter set for that study
2. You can create additional named parameter sets (e.g., "easy-version", "hard-version")
3. Each parameter set gets a unique URL parameter that you can share with different participant groups
4. All parameter sets for a test are stored separately, so you can have multiple active configurations

Note: The interface for creating named parameter sets is available through the parameter configuration page.

Step-by-Step Guide

Step 1: Access Your Study

1. Log in to the PEBL Online Platform
2. Go to My Research Studies
3. Click on your study name to open the management page

Step 2: Find the Configure Button

On the study management page:

1. Navigate to the Individual Tests or Test Chains tab
2. Find the test you want to configure
3. Click the ⚙️ Configure button next to the test name

Figure 1: Each test card displays a Configure button (⚙️) that opens the parameter configuration interface. The button is visible when the study is inactive.

Step 3: View Current Parameters

The configuration interface displays:

Header Section:

• Test name and description
• Your study name and token
• Link back to study management

Parameter Form: Each parameter shows:

• Parameter name (e.g., dopractice, isi, numtrials)
• Description explaining what it does
• Input field with current value
• Type and default information below the input

Figure 2: The parameter configuration page displays all configurable parameters for the selected test. Each parameter includes a name, description, input field, and type information. Click "Save Configuration" at the bottom when you're done making changes.

Step 4: Modify Parameters

Adjust parameters based on your research needs:

For Boolean Parameters (checkboxes):

• ☑️ Checked = 1 (enabled/true)
• ☐ Unchecked = 0 (disabled/false)

Figure 3: Boolean parameters appear as checkboxes. Check the box to enable (1) or uncheck to disable (0). Common boolean parameters include practice trial settings, feedback options, and randomization flags.

For Integer Parameters (number fields):

• Enter whole numbers only
• Common for: trial counts, timing (milliseconds), display sizes

Figure 4: Integer parameters use number input fields for whole numbers. These commonly control trial counts, timing intervals (in milliseconds), display dimensions, and other numeric settings.

For Float Parameters (decimal number fields):

• Enter decimal numbers
• Common for: probabilities, scaling factors, rates

For String Parameters (text fields):

• Enter text values
• Common for: file paths, response keys, labels

Step 5: Save Configuration

1. Review all your changes
2. Click 💾 Save Configuration at the bottom
3. You'll see a success message: "Parameters saved successfully to: {test}.par.json"
4. The parameter URL is displayed for reference

Step 6: Test Your Changes

Always test after changing parameters:

1. Return to the study management page
2. Click ▶ Try it out to run the test with your new settings
3. Verify the changes work as expected
4. Adjust and re-save if needed

Creating Multiple Parameter Sets

You can create multiple named configurations for the same test to run different variants in the same study.

When to Use Multiple Parameter Sets

Common scenarios:

• Difficulty levels: Create "easy", "medium", and "hard" versions with different trial counts or time limits
• Age groups: Different timing parameters for children vs. adults
• A/B testing: Test two variations of parameters to see which works better
• Pilot vs. Full: Short version for pilot testing, full version for main study

How to Create a Named Parameter Set

1. Configure the default parameters first: Follow Steps 1-5 above to set your first configuration
2. Save with default name: The first save creates the default parameter set
3. Create additional sets:

• Return to the Configure page
• Modify parameters for your variant
• Save with a custom name (e.g., "hard-version", "child-timing", "pilot")

4. Each set gets a unique URL: You can distribute different URLs to different participant groups

Using Different Parameter Sets

Each named parameter set can be accessed through the test's URL with a special parameter:

Default parameters:

https://your-site.com/runtime/pebl-launcher.html?test=corsi&token=YOUR<em>TOKEN

Named parameter set (e.g., "hard-version"):

https://your-site.com/runtime/pebl-launcher.html?test=corsi&token=YOUR</em>TOKEN&params=hard-version

Important: The parameter set name must exactly match what you saved (case-sensitive, no spaces recommended).

Managing Multiple Parameter Sets

• View all sets: The Configure page shows which parameter sets exist for the test
• Edit a set: Select the parameter set name and modify values
• Delete a set: Remove unused parameter configurations
• Default fallback: If you don't specify ¶ms=, the default parameter set is always used

Understanding Parameter Types

Boolean (Checkbox)

Purpose: Enable or disable features

Examples:

• dopractice - Whether to include practice trials
• usebeep - Whether to play audio feedback
• feedback - Whether to show performance feedback

Values:

• Unchecked (0): Feature disabled/false
• Checked (1): Feature enabled/true

Important: Some tests use -1 for special cases (e.g., backward recall direction)

Integer (Number Field)

Purpose: Whole number values for counts and timing

Examples:

• isi (Inter-Stimulus Interval) - Time between items (milliseconds)
• iti (Inter-Trial Interval) - Time between trials (milliseconds)
• numtrials - Total number of trials
• timeout - Maximum response time (milliseconds)

Tips:

• Timing parameters are usually in milliseconds (1000 ms = 1 second)
• Start with defaults and adjust gradually
• Test with pilot participants before finalizing

Float (Decimal Number Field)

Purpose: Decimal values for proportions and rates

Examples:

• probability - Event probability (0.0 to 1.0)
• difficulty - Difficulty scaling factor
• ratio - Proportion or rate values

Tips:

• Probabilities typically range from 0.0 (never) to 1.0 (always)
• Small changes can have large effects on difficulty

String (Text Field)

Purpose: Text values for file paths and keys

Examples:

• stimulusfile - Path to stimulus list
• responsekeys - Which keys participants press
• language - Language code for instructions

Tips:

• Be careful with file paths (case-sensitive)
• Response keys are usually single characters

Common Configuration Tasks

Disable Practice Trials

When: Participants are experienced or for repeated testing

Steps:

1. Find dopractice parameter
2. Uncheck the checkbox
3. Save

Effect: Test starts immediately with experimental trials

Adjust Timing

When: Adapting for different populations (children, elderly, clinical)

Examples:

Increase ISI (more time between stimuli):

isi: 1000 → 1500

Gives participants more processing time

Increase Timeout (more time to respond):

timeout: 2000 → 4000

Reduces pressure for populations with slower response times

Decrease ITI (faster pacing):

iti: 1000 → 500

Speeds up the test for experienced participants

Tips:

• Change one timing parameter at a time
• Test the feel with pilot participants
• Document baseline vs. modified values

Modify Trial Counts

When: Adjusting test length or difficulty

Examples:

Increase Trials (more data, longer test):

numtrials: 20 → 30
numreps: 10 → 15

Decrease Practice (shorter warm-up):

practicereps: 5 → 2

Tips:

• More trials = better reliability but longer test
• Balance statistical power with participant fatigue
• Consider total battery length (aim for < 45 minutes)

Change Difficulty

When: Adapting for different age groups or clinical populations

Examples:

Make Easier:

• Increase timeout (more time to respond)
• Decrease number of trials
• Reduce stimulus complexity
• Add more practice

Make Harder:

• Decrease timeout (less time to respond)
• Increase number of trials
• Remove practice trials
• Increase difficulty parameter value

Parameter Reference by Test Category

Memory Tests (Corsi, Memory Span, etc.)

Key Parameters:

• startlength / endlength - Range of sequence lengths to test
• timesperlength - Number of trials at each length
• direction - Forward (1) or backward (-1) recall
• isi - Time between items in sequence
• iti - Time between trials

Common Modifications:

• Backward spans only: Set direction to -1
• Shorter test: Reduce timesperlength from 2 to 1
• Easier: Increase isi from 1000 to 1500 ms

Attention Tests (Flanker, ANT, Go/No-Go)

Key Parameters:

• numreps - Repetitions per condition
• practicereps - Number of practice trials
• fixationtime - Duration of fixation cross (ms)
• timeout - Maximum response time (ms)
• iti - Time between trials (ms)

Common Modifications:

• Shorter test: Reduce numreps from 20 to 15
• More practice: Increase practicereps from 10 to 20
• Slower pacing: Increase fixationtime and iti

Executive Function Tests (WCST, Tower of London)

Key Parameters:

• numtrials - Total number of trials/problems
• feedback - Show performance feedback (1/0)
• timeout - Time limit per trial (ms)
• difficulty - Problem difficulty level

Common Modifications:

• Remove feedback: Set feedback to 0
• More time: Increase timeout
• Fewer problems: Decrease numtrials

Response Tests (Choice RT, Tapping)

Key Parameters:

• numtrials - Number of response trials
• timeout - Maximum response time (ms)
• isi / iti - Timing intervals
• feedback - Performance feedback (1/0)

Common Modifications:

• Quick version: Reduce numtrials
• Longer RSI: Increase isi

Best Practices

1. Test Before Deploying

Always test parameter changes yourself:

• Run through the entire test
• Verify timing feels appropriate
• Check that instructions match the configuration
• Ensure data uploads correctly

2. Document Your Changes

Keep a research log noting:

Study: Spatial Memory Pilot
Date: 2025-10-31 Test: Corsi Block Changes:
isi: 1000 → 1200 (slower pace for elderly participants)
dopractice: 1 → 0 (participants are experienced)
timesperlength: 2 → 3 (more data per length)
Reason: Adapting for age 65+ population

3. Change One Thing at a Time

When troubleshooting or optimizing:

• Change a single parameter
• Test the effect
• Document the result
• Repeat

Changing multiple parameters simultaneously makes it hard to identify what caused improvements or problems.

4. Consider the Full Battery

If running multiple tests:

• Calculate total estimated time
• Aim for < 45 minutes total
• Consider participant fatigue effects
• Place easier/shorter tests first

5. Use Consistent Timing

Within a battery:

• Keep ISI/ITI consistent across similar tests
• Use the same timeout values for comparable tasks
• Maintain consistent practice trial counts

This improves the participant experience and data comparability.

6. Keep Defaults Unless Necessary

The default parameters are chosen for general research use:

• Evidence-based timing values
• Appropriate trial counts
• Balanced difficulty

Only change parameters when you have a specific reason (population adaptation, research question, time constraints).

Troubleshooting

Parameters Not Saving

Problem: Click save but see error message

Causes:

• Not logged in (session expired)
• Don't have edit permissions for this study
• Invalid parameter values

Solutions:

1. Refresh the page and log in again
2. Verify you're the study owner or have edit permissions
3. Check that all values are valid for their type (e.g., numbers not text)
4. Contact administrator if permissions issue persists

Parameters Not Loading in Test

Problem: Test runs with defaults instead of your custom parameters

Causes:

• Configuration wasn't saved successfully
• Browser cache showing old version
• Token mismatch in URL

Solutions:

1. Verify configuration saved (check for success message)
2. Hard refresh the test page (Ctrl+F5 or Cmd+Shift+R)
3. Check that study token in URL matches your study
4. Re-save the configuration

Wrong Values Displayed

Problem: Configuration page shows different values than you saved

Causes:

• Someone else modified the parameters
• Browser showing cached version
• Multiple studies using same test with different configs

Solutions:

1. Refresh the page to reload from server
2. Check study analytics for recent activity
3. Verify you're viewing the correct study's configuration
4. Re-save your intended values

Checkbox Always Checked/Unchecked

Problem: Boolean parameter won't change state

Causes:

• JavaScript error on page
• Test requires that parameter to have a specific value
• Browser issue

Solutions:

1. Check browser console (F12) for errors
2. Try a different browser
3. Verify the parameter is actually modifiable (check test documentation)

Advanced: Parameter Files

Behind the scenes, your configurations are stored as JSON files:

Location: data/{YOUR_TOKEN}/{test}.par.json

Example (Corsi test):

{
"dopractice": 0, "direction": 1, "useCorsiPoints": 1, "startlength": 2, "endlength": 9, "timesperlength": 3, "isi": 1200, "iti": 1000, "usebeep": 1
}

What this means: Each study (token) has its own directory, so different studies can use different configurations for the same test.

Multiple Variants

Some tests have multiple variants (e.g., Memory Span with "staircase" and "buildup"):

• Each variant has separate parameters
• Separate configuration pages
• Separate parameter files: {test}-{variant}.par.json

Related Topics

• Test Parameters Reference - Complete list of parameters for each test
• Getting Started - Basic study setup
• Creating Test Chains - Configure parameters for batteries
• Troubleshooting - Solving common problems

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Need more help? Contact your platform administrator or consult the PEBL documentation for test-specific questions.

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Related Topics

• Getting Started
• Test Parameters Reference
• Troubleshooting Parameters