Attention
Apparent Motion Task
Also called: Ternus display, Ternus-Pikler display, Ternus effect, element and group motion, bistable apparent motion
Measure how the eye links two brief flashes into one movement: three dots flash twice in the Ternus display, and people say whether one dot jumped or all three moved together.
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. Try it here first, with no account.
- Papers, 2021 to 2025
- 211
- Evidence grade
- C
- Registered clinical studies
- 0
What it measures
A measure of how the eye links two brief flashes into one movement, with the Ternus display. Three dots flash in a row, then flash again one place along after a short gap. With short gaps most people see one dot jump from one end to the other; with longer gaps they see all three move together. Participants press one key for each. The score is the gap at which the two answers are equally likely. The flashes have no right answer.
Constructs
- Apparent motion
- Motion correspondence
- Perceptual grouping in time
Research uses
- Visual motion and perception research
- Individual differences in perception
- Within-study group comparison
How the paradigm works
The Apparent Motion Task measures how the visual system links two brief flashes into one movement, with the Ternus display (Ternus, 1926; Pantle and Picciano, 1976). Three dots in a row flash, and after a short empty gap they flash again one place along, so two of the positions are filled in both frames. The same two frames can look like one dot jumping from one end of the row to the other while the other two stay put (element motion) or like all three dots moving together (group motion). Short gaps favor the first and longer gaps the second, and the gap at which the percept changes differs from person to person (Petersik and Rice, 2006; Wang and colleagues, 2015).
More about the paradigm
On each trial a cross shows for 500 ms at the middle of the row and the panel stays empty for 300 to 500 ms. The dots then flash for 33 ms (two frames of a 60 Hz screen) and again one place along after a gap of 17, 50, 83, 117, 150, 183, 217 or 250 ms, moving right on half the trials. The participant presses F if one dot jumped or J if all three moved together, with no time limit. Each gap is shown 12 times (standard; 8 to 20). 8 check displays are added in which the dots really move between the same two frames: the end dot hops over the other two, or all three slide one place. That gives 104 trials in a seeded order with a rest halfway, after 6 practice check displays with feedback and 4 practice flash displays, about 6 to 8 minutes. Every display is set before the session: no answer changes a later trial, and there is no staircase or training mode. Desktop and laptop only.
The main score is the transition gap: the gap at which "all three moved together" and "one dot jumped" are equally likely, from a cumulative Gaussian fitted to the answers (as Wang and colleagues, 2015, and Zhang, Chen and Zhou, 2012, fitted them). Higher means longer gaps were needed before the dots were seen moving together. The spread of the answers and the share of group answers at each gap are also reported. The flash displays have no right answer, and no answer to one counts as an error; the check displays show whether the keys followed the display. The dots are drawn in screen pixels, so their size and spacing in degrees of visual angle depend on the screen and the viewing distance, which can change the transition gap: compare groups on similar equipment. Scores support research and do not diagnose.
Scores
- Transition Gapms
- The gap between the two frames at which "all three moved together" and "one dot jumped" are equally likely, from a cumulative Gaussian fitted to the answers.
- Higher means longer gaps were needed before the dots were seen moving together; not better or worse
- Spread of Answersms
- Half the distance between the gaps at which group answers are 25% and 75% likely, from the fitted curve.
- Smaller means a sharper change from one percept to the other
- Lapse Rate%
- Fitted share of answers that did not depend on the gap.
- Informational
- Fit%
- Share of the variance of the answers across gaps that the fitted curve explains.
- Informational
- Group Answers by Gap%
- Share of "all three moved together" answers at each gap, keyed by its ms.
- Rises with the gap; it crosses 0.5 at the transition gap
- Group Answers%
- Share of "all three moved together" answers over all flash displays.
- Informational
- Check Display Accuracy%
- Share of the check displays, in which the dots really moved, answered right, when at least 4 were answered.
- Below 0.5 is invalid and below 0.75 is flagged for review
- Median Answer Timems
- Median time from the end of the display to the answer.
- Informational; the answer has no time limit
- Anticipationscount
- Answers under 100 ms from the end of the display, which are not scored.
- Lower is better
- Early Key Pressescount
- F or J pressed before the display ended, which are not taken as answers.
- Informational
- Frame Intervalms
- Median time between screen frames during the displays.
- About 16.7 on a 60 Hz screen
- Dropped Frames%
- Share of the frames the browser skipped while the dots were shown.
- Above 0.05 is flagged for review
- Gaps Shown as Planned%
- Share of the flash displays whose measured gap lay within half a frame of the planned gap.
- Below 0.9 is flagged for review
- Frame Durationms
- Median measured time each frame of dots was on screen.
- About 33.3 on a 60 Hz screen
- Completed Trialstrials
- Displays answered in the scored run.
- Fewer than planned is flagged for review
- Planned Trialstrials
- Displays the run set out to show.
- Informational
Use and evidence
211 papers from 2021 to 2025 name this task in their title or abstract, down 23% compared with 2016 to 2020. That ranks it 136 of 495 test families in our census. See the counts for every test.
Show the numbers
| Year | Papers |
|---|---|
| 2025 | 50 |
| 2024 | 27 |
| 2023 | 38 |
| 2022 | 55 |
| 2021 | 41 |
| 2020 | 34 |
| 2019 | 57 |
| 2018 | 63 |
| 2017 | 62 |
| 2016 | 59 |
| 2015 | 68 |
| 2014 | 82 |
| 2013 | 72 |
| 2012 | 75 |
| 2011 | 94 |
| 2010 | 164 |
| 2009 | 54 |
| 2008 | 68 |
| 2007 | 56 |
| 2006 | 60 |
| 2005 | 56 |
| 2004 | 57 |
| 2003 | 52 |
| 2002 | 54 |
| 2001 | 53 |
| 2000 | 40 |
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
- 1
- Papers on reliability or validity
- 46
- Registered clinical studies using it as an outcome
- 0
Note on the counts: includes touch and theory papers.
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
- On a dark panel: a cross for 500 ms at the middle of the row, an empty panel for 300 to 500 ms, then three white dots of 36 px in a row, 72 px apart, for 33 ms (two frames of a 60 Hz screen), and again one place along after the gap, moving right on half the trials.
- Gaps
- 17, 50, 83, 117, 150, 183, 217 or 250 ms between the two frames, each 12 times (standard; 8 to 20).
- Answer
- Press F if one dot jumped from one end of the row to the other or J if all three moved together, with no time limit. Keys pressed before the display ends are counted and not taken as answers.
- Check displays
- 8 displays in which the dots really move for 250 ms between the same two frames: the end dot hops over the other two, or all three slide one place. These have a right answer; the flash displays have none.
- Trials
- 12 at each of the 8 gaps (standard; 8 to 20) and 8 check displays: 104 trials in a seeded order, with a rest halfway.
- Practice
- 6 check displays with feedback for 1,000 ms, then 4 flash displays at 17 and 250 ms with no feedback.
- Fixed displays
- Every gap and display time is set before the session, and no answer changes a later trial: there is no staircase and no training mode.
- Score
- The gap at which "all three moved together" is answered as often as "one dot jumped", from a cumulative Gaussian fitted to the answers, in ms. Answers under 100 ms leave the score.
The display is the Ternus display with three dots, drawn in screen pixels with no calibration: the dots' size and spacing in degrees of visual angle depend on the screen and the viewing distance, which can change the transition gap, so compare groups on similar equipment. Answers to the flash displays are never scored as errors.
Quality checks
Each session is marked valid, needs review or invalid, with the reason, before you see its scores.
Scored rows: apparent_motion_test from the scored run, F when one dot jumped from one end of the row to the other or J when all three moved together, with no time limit. The flash displays have no right answer: either answer at any gap is the measure, so accuracy is not judged on them and no answer to one is ever an error. Only the check displays, in which the dots really move, have a right answer: with at least 4 answered, under half right invalidates and under three quarters is flagged. Answer times run from the end of the display; responses under 100 ms follow the timed-test rule. No transition gap, a run short of its planned displays, more than 5% of display frames dropped, or under 90% of flash displays with their gap shown as planned is flagged for review.
Why these rules
There is no correct option to compare with chance, so accuracy is not judged against chance. The same two frames can look like one dot jumping or like the row moving, and which one a person sees depends on the gap and on the person (Petersik and Rice, 2006), so a report about a flash display is never right or wrong. On a check display our code draws real movement, a hop over the other dots or a slide of all three, so wrong answers there mean the keys did not follow the display. The displays are timed in screen frames, so a display that dropped frames changed what was shown, and a hidden tab withholds the percentile.
No percentile. Scores and quality flags only.
Running this test
Settings you can change
| Setting | Standard | Allowed |
|---|---|---|
| Displays at each gap | 12 | 8 to 20 |
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 Apparent Motion Task in a web browser (ConductCognition task version 1.0.0, scoring version 1.0.0; Ternus, 1926; Pantle and Picciano, 1976), with the standard settings (displays at each gap: 12). The main score was transition gap (the gap between the two frames at which "all three moved together" and "one dot jumped" are equally likely, from a cumulative Gaussian fitted to the answers).
ConductCognition versions: task version 1.0.0, scoring version 1.0.0. Every export records the versions each session used, for a methods section.
- Ternus, J. (1926). Experimentelle Untersuchungen über phänomenale Identität. Psychologische Forschung, 7(1), 81-136. https://doi.org/10.1007/BF02424350The display: elements in a row shown in two frames, the second shifted by one place, and the question of which elements look like the same ones.
- Pantle, A., & Picciano, L. (1976). A multistable movement display: Evidence for two separate motion systems in human vision. Science, 193(4252), 500-502. https://doi.org/10.1126/science.941023Element movement at short gaps and group movement at longer ones; showing the frames to different eyes, or reversing their contrast, nearly removed element movement.
- Petersik, J. T., & Rice, C. M. (2006). The evolution of explanations of a perceptual phenomenon: A case history using the Ternus effect. Perception, 35(6), 807-821. https://doi.org/10.1068/p5522The standard display, three elements in each of two frames, and the accounts of why short gaps give element movement and longer ones group movement.
- Wang, Q., Guo, L., Bao, M., & Chen, L. (2015). Perception of visual apparent motion is modulated by a gap within concurrent auditory glides, even when it is illusory. Frontiers in Psychology, 6, 564. https://doi.org/10.3389/fpsyg.2015.00564Two frames of 30 ms with gaps of 50 to 230 ms, and the gap where both answers are equally likely from a fitted curve, about 133 ms with no sound.
- Zhang, H., Chen, L., & Zhou, X. (2012). Adaptation to visual or auditory time intervals modulates the perception of visual apparent motion. Frontiers in Integrative Neuroscience, 6, 100. https://doi.org/10.3389/fnint.2012.00100Each person's transition gap from a logistic fit to six gaps of 50 to 200 ms with 30 ms frames, about 114 to 120 ms on average.
- Stepper, M. Y., Moore, C. M., Rolke, B., & Hein, E. (2020). Illusory size determines the perception of ambiguous apparent motion. Psychonomic Bulletin & Review, 27(6), 1230-1238. https://doi.org/10.3758/s13423-020-01786-9F for element motion and J for group motion; group answers rose from about 6% with no gap to about 96% at 240 ms.
Source papers
- Ternus J (1926). Experimentelle Untersuchungen über phänomenale Identität. Psychologische Forschung, 7(1):81-136.Paradigm source, Adults
- Pantle A, Picciano L (1976). A multistable movement display: Evidence for two separate motion systems in human vision. Science, 193(4252):500-502.Paradigm source, Adults
Questions
How long does the Apparent Motion 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?
Transition Gap, Spread of Answers, Lapse Rate, Fit, Group Answers by Gap, Group Answers, Check Display Accuracy, Median Answer Time, Anticipations, Early Key Presses, Frame Interval, Dropped Frames, Gaps Shown as Planned, Frame Duration, Completed Trials and Planned Trials. Each session is also marked valid, needs review or invalid, with the reason.
How widely is the Apparent Motion Task used in research?
211 papers from 2021 to 2025 name it in their title or abstract, down 23% compared with 2016 to 2020. That ranks it 136 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 Apparent Motion Task have?
In the published research, 1 paper reports its test-retest reliability and 0 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?
Displays at each gap (8 to 20). 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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