Executive Function
Psychological Refractory Period Task
Also called: PRP task, PRP paradigm, psychological refractory period paradigm, dual-task interference task, central bottleneck task
Measure how much a second task slows when it overlaps a first: participants answer a colored circle with one hand and a shape with the other, 50 to 1,000 ms apart.
6-8 minTimed: desktop or laptop with a mouse or trackpad
Free to start: 10 free participants per account, then $0.99 per participant for academic research, or any yearly plan. Preview any test free after you sign up.
- Papers, 2021 to 2025
- 58
- Evidence grade
- D
- Registered clinical studies
- 1
What it measures
Measures how much a second task slows when it starts soon after a first. A colored circle appears, then a shape after a short or long delay, and participants answer the circle with the left hand and the shape with the right.
Constructs
- Dual-task coordination
- Response selection
- Processing speed
Research uses
- Dual-task and multitasking research
- Aging and attention research
- Within-study group comparison
How the paradigm works
The psychological refractory period (PRP) task measures how much a second task slows when it has to start before a first one is finished. On every trial a colored circle appears left of a central cross, and participants answer its color with the left hand: D for yellow, F for blue. After a delay of 50, 150, 300, 600 or 1,000 ms (the stimulus onset asynchrony, or SOA), a white square or triangle appears right of the cross, and participants answer its shape with the right hand: J for a square, K for a triangle. They answer the circle first and each one as quickly and accurately as they can. Both stimuli are visual, and the test plays no sounds.
More about the paradigm
The five SOAs each run 24 times in the standard session, 120 trials in a seeded random order with the colors and shapes balanced within each SOA, after 15 practice trials with feedback on each answer. Each trial starts with 500 ms of blank and a 500 ms cross; the second stimulus appears on the screen frame nearest its planned SOA, and the measured SOA is saved. Both stimuli stay until both keys are pressed or 2,500 ms after the shape appears. Each response time runs from its own stimulus.
The main score is the PRP effect: the mean response time to the shape at the shortest SOA minus at the longest. In the central bottleneck account (Pashler, 1994), choosing the second response waits until the first has been chosen, so the second response slows by nearly as much as the SOA shortens, and the response to the circle stays about the same. The scores give the mean response time of each task at each SOA, the slope of the second task's response time between the two shortest SOAs (near -1 ms per ms when the second task waits), the change in the first task's response time, accuracy on each task, the share of trials with the two keys pressed within 100 ms of each other (grouped responses) and trials with the shape answered first. Response times use trials with both answers right, neither under 100 ms, and the circle answered first. Responses under 100 ms count as anticipations. Scores support research and do not diagnose.
Scores
- PRP Effectms
- Mean response time to the shape at the 50 ms SOA minus at the 1,000 ms SOA, on usable trials.
- Lower means less slowing when the two tasks overlap
- Shape Response Time, 50 ms SOAms
- Mean response time to the shape, from its onset, when it followed the circle by 50 ms.
- Lower is faster
- Shape Response Time, 150 ms SOAms
- Mean response time to the shape, from its onset, when it followed the circle by 150 ms.
- Lower is faster
- Shape Response Time, 300 ms SOAms
- Mean response time to the shape, from its onset, when it followed the circle by 300 ms.
- Lower is faster
- Shape Response Time, 600 ms SOAms
- Mean response time to the shape, from its onset, when it followed the circle by 600 ms.
- Lower is faster
- Shape Response Time, 1,000 ms SOAms
- Mean response time to the shape, from its onset, when it followed the circle by 1,000 ms.
- Lower is faster
- Circle Response Time, 50 ms SOAms
- Mean response time to the circle on trials with a 50 ms SOA.
- Lower is faster
- Circle Response Time, 150 ms SOAms
- Mean response time to the circle on trials with a 150 ms SOA.
- Lower is faster
- Circle Response Time, 300 ms SOAms
- Mean response time to the circle on trials with a 300 ms SOA.
- Lower is faster
- Circle Response Time, 600 ms SOAms
- Mean response time to the circle on trials with a 600 ms SOA.
- Lower is faster
- Circle Response Time, 1,000 ms SOAms
- Mean response time to the circle on trials with a 1,000 ms SOA.
- Lower is faster
- Slope at Short SOAsscore
- Change in the shape's response time per ms of SOA from the 50 ms to the 150 ms SOA.
- Near -1 when the second response waits for the first
- Circle SOA Effectms
- Mean response time to the circle at the 50 ms SOA minus at the 1,000 ms SOA.
- Near 0 when the circle is answered first and on its own
- Circle Accuracy%
- Share of trials with the right key for the circle, at or after 100 ms.
- Higher is better
- Shape Accuracy%
- Share of trials with the right key for the shape, at or after 100 ms.
- Higher is better
- Both Correct%
- Share of trials with both answers right.
- Higher is better
- Grouped Responses%
- Share of trials with both answers, in order, whose second key came within 100 ms of the first.
- Over half is flagged
- Shape Answered Firstcount
- Trials on which the shape was answered before the circle.
- Over 20% of trials is flagged
- Anticipationscount
- Answers under 100 ms from their stimulus, counted over both tasks.
- Lower is better
- Missed Answerscount
- Trials with no answer to the circle or to the shape.
- Lower is better
- Usable Trials, 50 ms SOAtrials
- Usable trials at the shortest SOA.
- Fewer than 8 is flagged
- Usable Trials, 1,000 ms SOAtrials
- Usable trials at the longest SOA.
- Fewer than 8 is flagged
- Usable Trialstrials
- Trials with both answers right, neither under 100 ms, and the circle answered first.
- Informational
- Total Trialstrials
- Trials in the scored run.
- Informational
Use and evidence
58 papers from 2021 to 2025 name this task in their title or abstract, down 38% compared with 2016 to 2020. That ranks it 242 of 395 test families in our census. See the counts for every test.
Show the numbers
| Year | Papers |
|---|---|
| 2025 | 12 |
| 2024 | 11 |
| 2023 | 12 |
| 2022 | 11 |
| 2021 | 12 |
| 2020 | 20 |
| 2019 | 14 |
| 2018 | 22 |
| 2017 | 18 |
| 2016 | 19 |
| 2015 | 14 |
| 2014 | 18 |
| 2013 | 18 |
| 2012 | 23 |
| 2011 | 23 |
| 2010 | 20 |
| 2009 | 13 |
| 2008 | 19 |
| 2007 | 15 |
| 2006 | 16 |
| 2005 | 18 |
| 2004 | 14 |
| 2003 | 11 |
| 2002 | 15 |
| 2001 | 15 |
| 2000 | 7 |
Use grade D
30 to 99 papers from 2021 to 2025.
Evidence grade D
Little published measurement evidence found.
- Papers on test-retest reliability
- 0
- Papers on reliability or validity
- 7
- Registered clinical studies using it as an outcome
- 1
How the grades work
Use: A is 1,000 or more papers from 2021 to 2025, B 300 to 999, C 100 to 299, D 30 to 99 and E fewer than 30. Evidence: A means at least 25 papers report its test-retest reliability and at least 25 registered clinical studies use it as an outcome; B, at least 8 test-retest papers, and either 5 registered clinical studies or 150 reliability or validity papers; C, at least 2 test-retest papers, 30 reliability or validity papers or 3 registered clinical studies; D, little published measurement evidence found. The counts measure use. They include every paper that names the task in its title or abstract. Grades describe the published research on this task, not ConductCognition's version of it.
Source: ConductCognition test census 0.14.0, counted 31 October 2026 from OpenAlex and ClinicalTrials.gov.
Task design
The trial sequence as the test runs in ConductCognition.
- First task
- A circle left of the cross, yellow or blue, answered with the left hand: D for yellow, F for blue.
- Second task
- A white square or triangle right of the cross, answered with the right hand: J for a square, K for a triangle.
- Delays
- 50, 150, 300, 600 or 1,000 ms from the circle to the shape, shown on the nearest screen frame and saved as measured.
- Timing
- 500 ms of blank and a 500 ms cross, then both stimuli until both keys or 2,500 ms after the shape.
- Trial mix
- 24 trials at each delay (standard; 16 to 40), 120 in all, colors and shapes balanced within each delay, in a seeded random order.
- Practice
- 15 trials with feedback on each answer for 1,500 ms.
- Order
- The circle is answered first. Each response time runs from its own stimulus.
- Score
- Mean response time to the shape at the 50 ms delay minus at the 1,000 ms delay, on trials with both answers right and in order.
Both stimuli are visual, where many PRP studies give the first task a tone. The circle, the shapes, the keys and the five delays are ConductScience choices within the designs Pashler (1994) reviews.
Quality checks
Each session is marked valid, needs review or invalid, with the reason, before you see its scores.
Scored rows: refractory_period_test from the scored run, each with two two-choice answers (D or F for the circle, J or K for the shape; chance 50%) within 2,500 ms of the shape. Below chance invalidates and not above chance is flagged. One key on 90% of answers invalidates when accuracy is not above chance. Missed responses and responses under 100 ms follow the timed-test rule. Fewer than 8 usable trials at the shortest or longest delay, the shape answered first on over 20% of trials, or the two keys pressed within 100 ms of each other on over half of trials is flagged and withholds the percentile.
Why these rules
Accuracy significantly below chance (one-sided exact test, p < .05) cannot come from guessing; it means the response mapping was reversed or the task was not followed (Slick, Sherman and Iverson 1999 treat below-chance forced-choice performance as definite response bias). Chance-level accuracy can be a real result in impaired participants, so it is only flagged. One option on at least 90% of answered trials, when the correct options are balanced and accuracy is not above chance, means the answers did not depend on the items (the task counterpart of long-string responding in surveys; Curran 2016). Missed responses and responses under 100 ms keep the platform's timed-test rule: more than max(3, 25%) missed responses or more than max(2, 20%) responses under 100 ms invalidate, and any is flagged. A response under 100 ms cannot be a reaction to the stimulus. The PRP effect is a difference between two means of the second task's response time, so it needs enough usable trials at both delays, the circle answered first and the two answers given one after the other (Pashler 1994; Ulrich and Miller 2008 on grouped responses). The limits of 8 trials, 20% and 50% and the 100 ms grouping window are ConductScience choices.
Running this test
Settings you can change
| Setting | Standard | Allowed |
|---|---|---|
| Trials per delay | 24 | 16 to 40 |
Yearly plans can change settings within these limits. Free and pay-as-you-go studies use the standard settings.
Need a setting this test does not have?
Devices and languages
- Timed test: participants need a desktop or laptop with a mouse or trackpad. Participant devices
- Languages: English, Spanish, French, German, Italian, Portuguese (Brazil), Chinese (Simplified) and Japanese.
- Available on: Every plan, including the free plan.
- Recruiting online? See the setup guides for Prolific, Sona Systems, CloudResearch Connect and Qualtrics.
Cite and describe
Participants completed the Psychological Refractory Period Task in a web browser (ConductCognition task version 1.0.0, scoring version 1.0.0; Telford, 1931; Welford, 1952; Pashler, 1994), with the standard settings (trials per delay: 24). The main score was PRP effect (mean response time to the shape at the 50 ms SOA minus at the 1,000 ms SOA, on usable trials).
ConductCognition versions: task version 1.0.0, scoring version 1.0.0. Every export records the versions each session used, for a methods section.
- Pashler, H. (1994). Dual-task interference in simple tasks: Data and theory. Psychological Bulletin, 116(2), 220-244. https://doi.org/10.1037/0033-2909.116.2.220The paradigm: two choice tasks at varied SOAs, the first answered first, and the central bottleneck account of the slowing.
- Telford, C. W. (1931). The refractory phase of voluntary and associative responses. Journal of Experimental Psychology, 14(1), 1-36. https://doi.org/10.1037/h0073262The first report of the slowing.
- Welford, A. T. (1952). The 'psychological refractory period' and the timing of high-speed performance: A review and a theory. British Journal of Psychology, 43(1), 2-19. https://doi.org/10.1111/j.2044-8295.1952.tb00322.x
- Pashler, H., & Johnston, J. C. (1989). Chronometric evidence for central postponement in temporally overlapping tasks. The Quarterly Journal of Experimental Psychology Section A, 41(1), 19-45. https://doi.org/10.1080/14640748908402351
- Ulrich, R., & Miller, J. (2008). Response grouping in the psychological refractory period (PRP) paradigm: Models and contamination effects. Cognitive Psychology, 57(2), 75-121. https://doi.org/10.1016/j.cogpsych.2007.06.004Grouped responses, which the grouped-response share reports.
- Strobach, T., Schütz, A., & Schubert, T. (2015). On the importance of Task 1 and error performance measures in PRP dual-task studies. Frontiers in Psychology, 6, 403. https://doi.org/10.3389/fpsyg.2015.00403Reporting the first task's response times and both tasks' errors.
- Glass, J. M., Schumacher, E. H., Lauber, E. J., Zurbriggen, E. L., Gmeindl, L., Kieras, D. E., & Meyer, D. E. (2000). Aging and the psychological refractory period: Task-coordination strategies in young and old adults. Psychology and Aging, 15(4), 571-595. https://doi.org/10.1037/0882-7974.15.4.571The PRP effect in younger and older adults.
Source papers
- Pashler H (1994). Dual-task interference in simple tasks: data and theory. Psychological Bulletin, 116(2):220-244.Paradigm source, Adults
Questions
How long does the Psychological Refractory Period Task take?
About 6 to 8 minutes, as listed in the test library.
What device does a participant need?
Timed test: participants need a desktop or laptop with a mouse or trackpad. The browser must be Chrome, Edge, Firefox or Safari.
What scores does it produce?
PRP Effect, Shape Response Time, 50 ms SOA, Shape Response Time, 150 ms SOA, Shape Response Time, 300 ms SOA, Shape Response Time, 600 ms SOA, Shape Response Time, 1,000 ms SOA, Circle Response Time, 50 ms SOA, Circle Response Time, 150 ms SOA, Circle Response Time, 300 ms SOA, Circle Response Time, 600 ms SOA, Circle Response Time, 1,000 ms SOA, Slope at Short SOAs, Circle SOA Effect, Circle Accuracy, Shape Accuracy, Both Correct, Grouped Responses, Shape Answered First, Anticipations, Missed Answers, Usable Trials, 50 ms SOA, Usable Trials, 1,000 ms SOA, Usable Trials and Total Trials. Each session is also marked valid, needs review or invalid, with the reason.
How widely is the Psychological Refractory Period Task used in research?
58 papers from 2021 to 2025 name it in their title or abstract, down 38% compared with 2016 to 2020. That ranks it 242 of 395 test families in the ConductCognition test census (use grade D). Source: ConductCognition test census 0.14.0, counted 31 October 2026 from OpenAlex and ClinicalTrials.gov.
How much reliability evidence does the Psychological Refractory Period Task have?
In the published research, 0 papers report its test-retest reliability and 1 registered clinical study uses it as an outcome (evidence grade D in the ConductCognition test census).
Which settings can a researcher change?
Trials per delay (16 to 40). Settings can be changed on yearly plans; free and pay-as-you-go studies use the standard settings.
Which languages can participants use?
Participants can take this test in English, Spanish, French, German, Italian, Portuguese (Brazil), Chinese (Simplified) and Japanese. English is on every plan, and the other languages come with yearly plans. Have a native speaker read the machine-translated text before launch.
Is this a clinical test?
No. ConductCognition is for research use only. It runs, scores and exports the test; clinical interpretation is outside the platform.
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