Reading
Letter Detection Task
Also called: missing-letter effect task, letter search in prose, letter detection in reading
Measure the letters people miss while reading short English passages. Participants mark every t, with omissions compared between function words such as the and other words.
5-7 minUntimed
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
- 4
- Evidence grade
- D
- Registered clinical studies
- 0
Find every t
The little boat rests at the wooden steps.
What it measures
Measures which letters readers miss in connected text. Participants read original English passages once and click every t, then answer a content question. Scores the difference in missed letters between function words such as the and content words, with false marks, reading time and comprehension.
Constructs
- Letter detection during reading
- Word-level and letter-level processing
- Reading comprehension
Research uses
- Reading research
- Research on the missing-letter effect
- Within-study group comparison
How the paradigm works
The Letter Detection Task measures which letters readers miss while following connected text. Participants read an English passage once at their normal pace and click every t, including capital T, then answer a question about its meaning. The main score is the missed-target proportion in function words such as the and to minus that in content words. Positive values indicate the missing-letter effect.
More about the paradigm
The method draws on the letter-detection literature reviewed by Healy (1994). This version has six original everyday passages, one practice passage and a content question after each. Every letter can be marked, so false marks are recorded too. The target is always t. Passages appear once in a seeded order, with two or four as shorter settings. Text and content questions are in English in every session; instructions are in the participant's language.
Scores
- Function-word Omission Effect%
- Missed target share in function words minus missed share in content words.
- Positive means more t letters were missed in function words; compare groups.
- Function-word Miss Rate%
- Unmarked target letters divided by all targets in the defined function words.
- Describes omissions while reading grammatical words such as the and to.
- Content-word Miss Rate%
- Unmarked target letters divided by targets in content words.
- Read alongside the function-word rate.
- Letters Found%
- Marked target letters divided by all target letters.
- Higher means more targets marked.
- False Markscount
- Distinct non-target letters marked.
- More than two flags for review.
- Function-word Targetscount
- Target letters in function words in scored passages.
- Denominator for function-word omissions.
- Content-word Targetscount
- Target letters in content words in scored passages.
- Denominator for content-word omissions.
- Median Passage Timems
- Median time from a passage appearing to Done, including marking.
- Describes reading and marking time together.
- Content Questions Correct%
- Correct share of answered content questions from the selected run.
- Below half correct flags for review.
- Completed Passagescount
- Test passages recorded in the selected run.
- All planned passages should be completed.
- Planned Passagescount
- Number of passages set before the run.
- Two, four or six.
- Early Endingscount
- Passages ended in under 100 ms, excluded from letter measures.
- Any such passage invalidates the run.
- Session in Another Language0/1
- 1 when the session ran in a language other than English; the passages are English in every session.
- 1 is flagged for review.
Use and evidence
4 papers from 2021 to 2025 name this task in their title or abstract. That ranks it 478 of 495 test families in our census. See the counts for every test.
Show the numbers
| Year | Papers |
|---|---|
| 2025 | 0 |
| 2024 | 0 |
| 2023 | 3 |
| 2022 | 1 |
| 2021 | 0 |
| 2020 | 1 |
| 2019 | 0 |
| 2018 | 2 |
| 2017 | 0 |
| 2016 | 3 |
| 2015 | 3 |
| 2014 | 2 |
| 2013 | 1 |
| 2012 | 4 |
| 2011 | 1 |
| 2010 | 4 |
| 2009 | 2 |
| 2008 | 2 |
| 2007 | 4 |
| 2006 | 1 |
| 2005 | 3 |
| 2004 | 3 |
| 2003 | 1 |
| 2002 | 0 |
| 2001 | 2 |
| 2000 | 1 |
Use grade E
Fewer than 30 papers from 2021 to 2025.
Evidence grade D
Little published measurement evidence found.
- Papers on test-retest reliability
- 0
- Papers on reliability or validity
- 1
- Registered clinical studies using it as an outcome
- 0
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.
- Items
- 6 original English passages and 1 practice passage. English text and questions stay English in every session; instructions use the participant's language.
- Task
- Read each passage once for meaning, clicking every t or T without rereading. Marks stay visible and cannot be removed. Done ends the passage; there is no time limit.
- Session
- Choose 2, 4 or 6 test passages, drawn without repetition from the seed. Every length has equal true and false content questions. A 500 ms fixation lead-in separates starting a passage from the first mark.
- Scores
- Missed-target proportion in function words minus that in content words, both rates, detection rate, false marks, target counts, median passage time and content-question accuracy. Repeated clicks count once.
- Quality
- Every planned passage must be completed. Ending a passage under 100 ms or finding no target letters invalidates. Fewer than half the questions right or more than two false marks flags for review.
Our own passages follow the letter-detection method reviewed by Healy (1994). Clicking replaces circling on paper; passage time includes marking. Function and content words differ in frequency, length and letter position as well as grammatical role. No published norms are applied; scores support research and do not diagnose.
Quality checks
Each session is marked valid, needs review or invalid, with the reason, before you see its scores.
Scores marked letters in the selected run's English passages. Missing letters are the outcome, so no chance-accuracy rule is applied. Incomplete runs, passages ended under 100 ms and no targets found invalidate; comprehension below half correct or more than two false marks flags for review. A session in another language is flagged for review.
Why these rules
Omissions depend on word class and are the research outcome. There is no meaningful random-choice probability for marking any subset of a passage. The completion, early-ending and review thresholds are ConductScience choices. The word lists are English. A session run in another language shows English words to a participant who may not read English fluently, so it is flagged for review.
No percentile. Scores and quality flags only.
Running this test
Settings you can change
| Setting | Standard | Allowed |
|---|---|---|
| Test passages | 6 passages (standard) | 6 passages (standard), 4 passages, 2 passages |
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
- Untimed test: runs on desktops and laptops. Participant devices
- Instructions and screens: English, Spanish, French, German, Italian, Portuguese (Brazil), Chinese (Simplified) and Japanese. Words and sentences: English.
- 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 Letter Detection Task in a web browser (ConductCognition task version 1.0.0, scoring version 1.0.0; Healy, 1994), with the standard settings (test passages: 6 passages). The main score was function-word omission effect (missed target share in function words minus missed share in content words).
ConductCognition versions: task version 1.0.0, scoring version 1.0.0. Every export records the versions each session used, for a methods section.
- Healy, A. F. (1994). Letter detection: A window to unitization and other cognitive processes in reading text. Psychonomic Bulletin & Review, 1(3), 333-344. https://doi.org/10.3758/BF03213975
Source papers
- Healy AF (1994). Letter detection: A window to unitization and other cognitive processes in reading text. Psychonomic Bulletin & Review, 1(3):333-344.Paradigm source, Adults who read English
Questions
How long does the Letter Detection Task take?
About 5 to 7 minutes, as listed in the test library.
What device does a participant need?
Untimed test: runs on desktops and laptops. The browser must be Chrome, Edge, Firefox or Safari.
What scores does it produce?
Function-word Omission Effect, Function-word Miss Rate, Content-word Miss Rate, Letters Found, False Marks, Function-word Targets, Content-word Targets, Median Passage Time, Content Questions Correct, Completed Passages, Planned Passages, Early Endings and Session in Another Language. Each session is also marked valid, needs review or invalid, with the reason.
How widely is the Letter Detection Task used in research?
4 papers from 2021 to 2025 name it in their title or abstract. That ranks it 478 of 495 test families in the ConductCognition test census (use grade E). Source: ConductCognition test census 0.22.0, counted 3 November 2026 from OpenAlex and ClinicalTrials.gov.
How much reliability evidence does the Letter Detection Task have?
In the published research, 0 papers report its test-retest reliability and 0 registered clinical studies use it as an outcome (evidence grade D in the ConductCognition test census).
Does it report a percentile?
No. Scores and quality flags only.
Which settings can a researcher change?
Test passages (6 passages (standard), 4 passages, 2 passages). Settings can be changed on yearly plans; free and pay-as-you-go studies use the standard settings.
Which languages can participants use?
The instructions and screens are in English, Spanish, French, German, Italian, Portuguese (Brazil), Chinese (Simplified) and Japanese. The words and sentences stay in English, so sessions in other languages are flagged for review. 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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