Attention
Perceptual Load Task
Also called: load theory task, perceptual load paradigm, letter search task with distractors, Lavie task, response competition under load
Measure whether a hard search shuts out a distractor that an easy search lets in: participants find an X or N in a ring of letters while a letter outside the ring matches it or not.
7-9 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. Try it here first, with no account.
- Papers, 2021 to 2025
- 221
- Evidence grade
- C
- Registered clinical studies
- 2
What it measures
Measures how much an easy or a hard search lets a letter that should be ignored slow the answer. A ring of letters flashes, and participants press X or N for the letter it holds while another letter outside the ring matches it or not. A hard search usually leaves less room for that letter to interfere.
Constructs
- Selective attention
- Perceptual load
- Distractor interference
Research uses
- Selective attention research
- Distraction research
- Within-study group comparison
How the paradigm works
The Perceptual Load Task measures whether a letter that should be ignored still slows the answer when the main task is easy, and stops doing so when it is hard. In load theory (Lavie, 1995), perception has a limited capacity: a demanding search uses it up, so a distractor goes unprocessed, while an easy search leaves capacity that takes the distractor in. In the display of Lavie and Cox (1997), people find an X or an N in a ring of letters, among small Os (low load) or among other angular letters (high load), while a distractor letter outside the ring matches the target or not. A distractor that does not match slows the answer far more in low-load search: in Forster and Lavie (2008), the interference was 36 ms under low load and -4 ms under high load.
More about the paradigm
Six letters on a ring flash for 200 ms on a dark panel after a 500 ms cross. The ring always holds one X or one N, and participants press the X or the N key within 2,000 ms of the ring's onset. In low-load blocks the other five letters are small Os; in high-load blocks they are five of H, K, M, V, W and Z. A larger X or N appears to the left or right of the ring on every trial: the same as the target on half the trials (compatible) and the other target on the rest (incompatible). Each block of 48 trials holds one load, and the standard session has four blocks in the order ABBA, 192 trials, after 12 practice trials of each load with feedback. In the test, only a wrong, slow or early answer gets a message.
The primary score is the distractor interference under low load minus under high load, where the interference is the mean correct response time with an incompatible distractor minus with a compatible one. Positive values mean the hard search left the distractor less room to interfere, as load theory predicts. The task also reports the interference in each load, the four cell means, the slowing from low to high load, which shows that the high-load search was harder, and accuracy and interference in errors for each load. Means use correct answers at or after 100 ms with no key pressed before the ring, without those more than 3 SD from their cell's mean; responses under 100 ms and keys pressed before the ring count as anticipations.
Scores
- Interference, Low Minus High Loadms
- Distractor interference when the other ring letters were small Os minus when they were mixed capitals.
- Positive values mean the hard search left the distractor less room to interfere
- Distractor Interference, Low Loadms
- Mean correct response time with an incompatible distractor minus a compatible one, in low-load blocks.
- Positive values mean the distractor slowed answers
- Distractor Interference, High Loadms
- Mean correct response time with an incompatible distractor minus a compatible one, in high-load blocks.
- Positive values mean the distractor slowed answers
- Response Time, Low Load, Compatiblems
- Mean correct response time in low-load blocks with a compatible distractor, after trimming.
- Lower is faster
- Response Time, Low Load, Incompatiblems
- Mean correct response time in low-load blocks with an incompatible distractor, after trimming.
- Lower is faster
- Response Time, High Load, Compatiblems
- Mean correct response time in high-load blocks with a compatible distractor, after trimming.
- Lower is faster
- Response Time, High Load, Incompatiblems
- Mean correct response time in high-load blocks with an incompatible distractor, after trimming.
- Lower is faster
- Load Costms
- Mean correct response time in high-load blocks minus low-load blocks, after trimming.
- Positive values mean the high-load search took longer, as it should
- Accuracy%
- Share of test trials answered with the key for the letter in the ring.
- Higher is better
- Accuracy, Low Load%
- Share of low-load trials answered correctly, leaving out answers under 100 ms and keys pressed before the ring.
- Higher is better
- Accuracy, High Load%
- Share of high-load trials answered correctly, leaving out answers under 100 ms and keys pressed before the ring.
- Higher is better
- Error Interference, Low Load%
- Accuracy with a compatible distractor minus with an incompatible one, in low-load blocks.
- Positive values mean the distractor caused errors
- Error Interference, High Load%
- Accuracy with a compatible distractor minus with an incompatible one, in high-load blocks.
- Positive values mean the distractor caused errors
- Trials in the Smallest Celltrials
- Usable correct trials in the smallest of the four cells of load and compatibility, before trimming.
- Fewer than 24 is flagged
- Anticipationscount
- Answers under 100 ms from the ring's onset, or with a key pressed before the ring.
- Lower is better
- Missed Responsescount
- Test trials with no answer within 2,000 ms of the ring's onset.
- Lower is better
- Test Trialstrials
- Test trials in the scored run.
- Informational
Use and evidence
221 papers from 2021 to 2025 name this task in their title or abstract, down 13% compared with 2016 to 2020. That ranks it 131 of 495 test families in our census. See the counts for every test.
Show the numbers
| Year | Papers |
|---|---|
| 2025 | 70 |
| 2024 | 30 |
| 2023 | 45 |
| 2022 | 35 |
| 2021 | 41 |
| 2020 | 42 |
| 2019 | 46 |
| 2018 | 54 |
| 2017 | 53 |
| 2016 | 58 |
| 2015 | 40 |
| 2014 | 50 |
| 2013 | 51 |
| 2012 | 59 |
| 2011 | 63 |
| 2010 | 80 |
| 2009 | 42 |
| 2008 | 29 |
| 2007 | 24 |
| 2006 | 22 |
| 2005 | 9 |
| 2004 | 8 |
| 2003 | 7 |
| 2002 | 8 |
| 2001 | 4 |
| 2000 | 4 |
Use grade C
100 to 299 papers from 2021 to 2025.
Evidence grade C
At least 2 test-retest papers, 30 reliability or validity papers or 3 registered clinical studies.
- Papers on test-retest reliability
- 2
- Papers on reliability or validity
- 42
- Registered clinical studies using it as an outcome
- 2
Note on the counts: its 2 trial listings are off-topic.
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 0.22.0, counted 3 November 2026 from OpenAlex and ClinicalTrials.gov.
Task design
The trial sequence as the test runs in ConductCognition.
- Display
- Six letters on a ring of radius 64 px around the center of a dark panel, in a 32 px bold font, and a larger X or N, in a 44 px font, 136 px left or right of the center.
- Load
- Low: the other five ring letters are small Os. High: they are five different letters from H, K, M, V, W and Z, in a seeded order. Each block holds one load.
- Distractor
- On every trial, the same letter as the target (compatible) or the other target (incompatible), on the left or the right, each equally often.
- Timing
- 500 ms of empty panel, a 500 ms cross, then the ring for 200 ms, shown on animation frames with its measured duration saved. The answer counts within 2,000 ms of the ring's onset.
- Keys
- X for an X in the ring and N for an N.
- Trial mix
- 48 trials in a block: each target, ring position, distractor side and compatibility once, in a seeded order. Two blocks of each load in the order ABBA (standard), or four in the order ABBAABBA, the first load drawn for each session: 192 or 384 trials.
- Practice
- 12 trials of each load, in the order of the first two blocks, with feedback for 800 ms. In the test, only a wrong, slow or early answer gets a message, for 1,000 ms.
- Score
- Distractor interference (incompatible minus compatible mean correct response time) under low load minus under high load.
Forster and Lavie (2008) showed the ring until the answer, and Forster and Lavie (2009) for 100 ms; this version shows it for 200 ms, as Forster and colleagues (2014) did with their letter ring. Every trial has a distractor letter; the source's trials with no distractor and with cartoon pictures were not built. The keys are the letters X and N, in place of the source's number keys. Sizes are not calibrated to the screen; at a nominal 40 px per degree the ring and the letters have the source's sizes. Whether high load uses up capacity or the added letters dilute the distractor is debated (Tsal and Benoni, 2010; Lavie and Torralbo, 2010).
Quality checks
Each session is marked valid, needs review or invalid, with the reason, before you see its scores.
Scored rows: perceptual_load_test from the scored run, X or N for the letter in the ring (chance 50%, each key on half the trials of every block) within 2,000 ms of the ring's onset, correctness from the recorded key. Below chance invalidates and not above chance is flagged. One key on 90% of answers invalidates when accuracy is not above chance. Fewer than 24 usable correct trials in any of the four cells of load and compatibility is flagged and withholds the percentile. Keys pressed before the ring are held to the limit for responses under 100 ms. Missed responses and responses under 100 ms follow the timed-test rule.
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. A key pressed before the ring cannot be an answer to it, so it is held to the limit for responses under 100 ms. The primary score is a difference of two differences, so it needs enough correct trials in each of its four cells; the limit of 24, half of each cell in the standard session, is a ConductScience choice.
No percentile. Scores and quality flags only.
Running this test
Settings you can change
| Setting | Standard | Allowed |
|---|---|---|
| Blocks of each load | 2 (192 trials), standard | 2 (192 trials), standard, 4 (384 trials) |
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.
- No percentile. Scores and quality flags only. How norms work
- Recruiting online? See the setup guides for Prolific, Sona Systems, CloudResearch Connect and Qualtrics.
Cite and describe
Participants completed the Perceptual Load Task in a web browser (ConductCognition task version 1.0.0, scoring version 1.0.0; Lavie, 1995; Lavie and Cox, 1997), with the standard settings (blocks of each load: 2 (192 trials), standard). The main score was Interference, low minus high load (distractor interference when the other ring letters were small Os minus when they were mixed capitals).
ConductCognition versions: task version 1.0.0, scoring version 1.0.0. Every export records the versions each session used, for a methods section.
- Lavie, N. (1995). Perceptual load as a necessary condition for selective attention. Journal of Experimental Psychology: Human Perception and Performance, 21(3), 451-468. https://doi.org/10.1037/0096-1523.21.3.451Load theory, tested with a distractor that competes for the response: it interfered only under low load.
- Lavie, N., & Cox, S. (1997). On the efficiency of visual selective attention: Efficient visual search leads to inefficient distractor rejection. Psychological Science, 8(5), 395-398. https://doi.org/10.1111/j.1467-9280.1997.tb00432.xThe search among dissimilar letters (low load) or similar ones (high load), with a peripheral distractor.
- Forster, S., & Lavie, N. (2008). Failures to ignore entirely irrelevant distractors: The role of load. Journal of Experimental Psychology: Applied, 14(1), 73-83. https://doi.org/10.1037/1076-898x.14.1.73The ring of six letters, the targets X and N, the letters of each load, the distractor beside the ring and the ABBA order of blocks.
- Forster, S., & Lavie, N. (2009). Harnessing the wandering mind: The role of perceptual load. Cognition, 111(3), 345-355. https://doi.org/10.1016/j.cognition.2009.02.006The same ring shown for 100 ms.
- Forster, S., Robertson, D. J., Jennings, A., Asherson, P., & Lavie, N. (2014). Plugging the attention deficit: Perceptual load counters increased distraction in ADHD. Neuropsychology, 28(1), 91-97. https://doi.org/10.1037/neu0000020A letter ring shown for 200 ms, and high load reducing distraction in adults with and without ADHD.
- Tsal, Y., & Benoni, H. (2010). Diluting the burden of load: Perceptual load effects are simply dilution effects. Journal of Experimental Psychology: Human Perception and Performance, 36(6), 1645-1656. https://doi.org/10.1037/a0018172The dilution account of the reduced interference.
- Lavie, N., & Torralbo, A. (2010). Dilution: A theoretical burden or just load? A reply to Tsal and Benoni (2010). Journal of Experimental Psychology: Human Perception and Performance, 36(6), 1657-1664. https://doi.org/10.1037/a0020733The reply, with the ring task's control for the added letters.
Source papers
- Forster S, Lavie N (2008). Failures to ignore entirely irrelevant distractors: The role of load. Journal of Experimental Psychology: Applied, 14(1):73-83.N 16, Adults 18 to 35 (mean 22)
Questions
How long does the Perceptual Load Task take?
About 7 to 9 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?
Interference, Low Minus High Load, Distractor Interference, Low Load, Distractor Interference, High Load, Response Time, Low Load, Compatible, Response Time, Low Load, Incompatible, Response Time, High Load, Compatible, Response Time, High Load, Incompatible, Load Cost, Accuracy, Accuracy, Low Load, Accuracy, High Load, Error Interference, Low Load, Error Interference, High Load, Trials in the Smallest Cell, Anticipations, Missed Responses and Test Trials. Each session is also marked valid, needs review or invalid, with the reason.
How widely is the Perceptual Load Task used in research?
221 papers from 2021 to 2025 name it in their title or abstract, down 13% compared with 2016 to 2020. That ranks it 131 of 495 test families in the ConductCognition test census (use grade C). Source: ConductCognition test census 0.22.0, counted 3 November 2026 from OpenAlex and ClinicalTrials.gov.
How much reliability evidence does the Perceptual Load Task have?
In the published research, 2 papers report its test-retest reliability and 2 registered clinical studies use it as an outcome (evidence grade C in the ConductCognition test census).
Does it report a percentile?
No. Scores and quality flags only.
Which settings can a researcher change?
Blocks of each load (2 (192 trials), standard, 4 (384 trials)). 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.
Every test: the full test list.
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