Social Cognition
Chimeric Faces Task
Also called: chimeric faces test, chimeric face task, free-viewing chimeric faces, emotional chimeric faces, left hemiface bias task
Measure the perceptual bias toward the left side of faces: participants pick the happier of a half-smiling face and its mirror image, scored by how often the face smiling on the left is chosen.
5-7 minUntimed
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
- 23
- Evidence grade
- C
- Registered clinical studies
- 0
What it measures
Measures the perceptual bias toward the left side of faces. Each pair shows a face that smiles on one half above its mirror image, and participants pick the face that looks happier. The main score is the laterality score: how much more often the face smiling on the viewer's left is chosen.
Constructs
- Perceptual asymmetry for faces
- Hemispheric lateralization of emotion perception
- Left visual field bias
Research uses
- Lateralization of face and emotion processing in research on handedness, development and aging
- Group differences in perceptual asymmetry, at the group level
- Behavioral laterality batteries with other free-viewing tasks
How the paradigm works
The chimeric faces task measures a bias in how people see emotion in faces. Each chimeric face joins half of a smiling photograph to half of a neutral photograph of the same person, split down the middle of the face. The task shows a chimeric face above its mirror image and asks which face looks happier, by click, tap or the arrow keys, with no time limit. The two faces hold the same two halves, so neither is happier than the other; yet most right-handed adults choose the face with the smile on their left more often (Levy, Heller, Banich and Burton, 1983). The bias is usually read as right-hemisphere dominance for faces and emotion, since the left side of a face is seen first by the right hemisphere, and it varies reliably between people: Levy and colleagues found a split-half reliability of .93 (through Parker and colleagues, 2021).
More about the paradigm
The photographs come from the Face Research Lab London Set (DeBruine and Jones, 2017): 16 people, 8 women and 8 men chosen for clear smiles, each shown in grayscale in an oval that hides hair, ears and clothing. Each person has two chimeric faces, the smile on the left half of the photographs and on the right half, and each is shown with its mirror image twice, once with the face smiling on the left on top and once at the bottom: 64 pairs (32 in the short setting, each pair once). Four catch pairs show a smiling and a neutral photograph of one person, which has a right answer. A cross between the two faces comes before each pair. Four practice pairs come first.
The main score is the laterality score, (L - R) / (L + R), where L counts choices of the face smiling on the viewer's left and R choices of the face smiling on the right, from -1 to +1. Positive values mean a leftward bias. Levy and colleagues reported the reverse sign, (R - L) / (L + R), where a leftward bias is negative, as some later papers do. The task also reports the percent of left choices, the percent of upper-face choices (a position bias), how often the same face of a pair was chosen in both positions, the difference in choice time between the two kinds of choices (Bourne, 2008), accuracy on the catch pairs and the median choice time. Presses within 100 ms of the faces are counted as anticipations and not taken as answers. Scores support research and do not diagnose.
Scores
- Laterality Scorescore
- (L - R) / (L + R) over the answered chimera pairs, L and R the choices of the face smiling on the viewer's left and right, from -1 to +1. Positive means a leftward bias.
- Informational
- Left Smile Chosen%
- Percent of chimera pairs where the face smiling on the viewer's left was chosen.
- Informational
- Upper Face Chosen%
- Percent of chimera pairs where the upper face was chosen. The face smiling on the left is on top in half the pairs.
- Quality check
- Pair Consistency%
- Of the chimeras shown in both positions, the percent where the same face was chosen both times. Choosing by position alone gives 0.
- Quality check
- Choice Time Biasms
- Median time choosing the face smiling on the right minus median time choosing the face smiling on the left. Positive means faster choices of the left (Bourne, 2008).
- Informational
- Catch Pair Accuracy%
- Percent of the 4 catch pairs (a smiling and a neutral photograph) where the smiling face was chosen.
- Quality check
- Median Choice Timems
- Median time from the faces appearing to the choice on chimera pairs, over choices at or after 100 ms.
- Informational; the answer has no time limit
- Chimera Pairs Answeredtrials
- Chimera pairs answered in the scored run.
- Fewer than planned is flagged for review
- Planned Chimera Pairstrials
- Chimera pairs the session planned: 64, or 32 in the short setting, plus 4 catch pairs.
- Informational
- Anticipationscount
- Presses within 100 ms of the faces appearing, not taken as answers.
- Quality check
Use and evidence
23 papers from 2021 to 2025 name this task in their title or abstract, down 36% compared with 2016 to 2020. That ranks it 321 of 395 test families in our census. See the counts for every test.
Show the numbers
| Year | Papers |
|---|---|
| 2025 | 3 |
| 2024 | 7 |
| 2023 | 3 |
| 2022 | 3 |
| 2021 | 7 |
| 2020 | 7 |
| 2019 | 8 |
| 2018 | 7 |
| 2017 | 10 |
| 2016 | 4 |
| 2015 | 4 |
| 2014 | 11 |
| 2013 | 12 |
| 2012 | 6 |
| 2011 | 10 |
| 2010 | 20 |
| 2009 | 6 |
| 2008 | 8 |
| 2007 | 10 |
| 2006 | 6 |
| 2005 | 8 |
| 2004 | 7 |
| 2003 | 9 |
| 2002 | 6 |
| 2001 | 6 |
| 2000 | 5 |
Use grade E
Fewer than 30 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
- 3
- Papers on reliability or validity
- 13
- 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 0.14.0, counted 2 November 2026 from OpenAlex and ClinicalTrials.gov.
Task design
The trial sequence as the test runs in ConductCognition.
- Faces
- Grayscale photographs of 16 adults from the Face Research Lab London Set, 8 women and 8 men chosen for clear smiles, aligned on the eyes and cropped to an oval that hides hair, ears and clothing, up to 280 by 320 px each, one above the other on a black panel.
- Chimeras
- Each person's smiling and neutral photographs, split down the middle between the eyes and joined with a 10 px blend: one chimera with the smile on the left half of the photographs and one with it on the right half. Each is shown above or below its exact mirror image.
- Question
- Which face looks happier? Answered by click, tap, or the Up and Down arrow keys, with no time limit. A 500 ms cross between the two faces comes first, and a 500 ms blank follows each choice. Presses within 100 ms of the faces are counted and not taken as answers.
- Pairs
- 64 (standard; 32): each chimera with the face smiling on the left on top once and at the bottom once, or, in the short setting, once each with the positions balanced. The order is drawn for each session, with no person twice in a row and no more than 4 pairs in a row with the face smiling on the left in the same position.
- Catch pairs
- 4, a smiling and a neutral photograph of one person, the smiling face twice on top and twice at the bottom, one in each quarter of the pairs.
- Practice
- 4 pairs of two people the test does not use: a smiling and a neutral photograph with feedback, then a chimera with a note that it has no right answer, each for 1,500 ms.
The procedure follows the free-viewing test of Levy, Heller, Banich and Burton (1983) with photographs of our own: each person's two chimeras and their mirror images, positions counterbalanced, as Gupta and Pandey (2010) built theirs. The score is (L - R) / (L + R), positive for a leftward bias; Levy and colleagues reported the reverse sign. No screen names or labels a face. Its people include 12 of the Face Matching Task's 40, 9 of the Face Memory Test's 24 distractor faces and 8 of the Face-name Memory Task's 24 foils, so in a study with any of them, run this task after them or in a separate session.
Quality checks
Each session is marked valid, needs review or invalid, with the reason, before you see its scores.
Scored rows: chimeric_faces_test from the scored run, one choice of the happier face per pair with no time limit. The chimera pairs have no right answer, so accuracy is not judged against chance. The same position on at least 90% of choices invalidates. Catch pairs under 75% right (2 or more of 4 wrong) invalidate, and 1 wrong is flagged. Choices under 200 ms on at least half the pairs invalidate. A run short of its planned pairs is flagged for review.
Why these rules
There is no correct option to compare with chance, so accuracy is not judged against chance. The face smiling on the left is on top in half the pairs, so choosing one position nearly every time means the faces were not compared. A catch pair shows a smiling and a neutral photograph, so a wrong answer means the question was not followed; Speranza and colleagues (2025) excluded participants who failed 2 or more such checks. An answer under 200 ms is faster than a simple visual reaction, so it cannot reflect the item. Following response-time effort screening for untimed tests (Wise and Kong 2005), the session is invalid only when at least half the answers are that fast.
No percentile. Scores and quality flags only.
Running this test
Settings you can change
| Setting | Standard | Allowed |
|---|---|---|
| Number of pairs | 64 (standard) | 64 (standard), 32 |
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, laptops and tablets. 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 Chimeric Faces Task in a web browser (ConductCognition task version 1.0.0, scoring version 1.0.0; Levy, Heller, Banich & Burton, 1983), with the standard settings (number of pairs: 64). The main score was laterality score ((L - R) / (L + R) over the answered chimera pairs, L and R the choices of the face smiling on the viewer's left and right, from -1 to +1).
ConductCognition versions: task version 1.0.0, scoring version 1.0.0. Every export records the versions each session used, for a methods section.
- Levy, J., Heller, W., Banich, M. T., & Burton, L. A. (1983). Asymmetry of perception in free viewing of chimeric faces. Brain and Cognition, 2(4), 404-419. https://doi.org/10.1016/0278-2626(83)90021-0
- Gupta, G., & Pandey, R. (2010). Assessment of hemispheric asymmetry: Development and psychometric evaluation of a chimeric face test. Industrial Psychiatry Journal, 19(1), 30-36. https://doi.org/10.4103/0972-6748.77632Both chimeras of each person, each beside its mirror image, with positions counterbalanced.
- Coronel, J. C., & Federmeier, K. D. (2014). Task demands modulate decision and eye movement responses in the chimeric face test: Examining the right hemisphere processing account. Frontiers in Psychology, 5, 229. https://doi.org/10.3389/fpsyg.2014.00229A leftward bias when judging emotion, and none when the same faces are judged otherwise.
- Bourne, V. J. (2008). Chimeric faces, visual field bias, and reaction time bias: Have we been missing a trick? Laterality, 13(1), 92-103. https://doi.org/10.1080/13576500701754315Faster choices of the face smiling on the left.
- Parker, A. J., Woodhead, Z. V. J., Thompson, P. A., & Bishop, D. V. M. (2021). Assessing the reliability of an online behavioural laterality battery: A pre-registered study. Laterality, 26(4), 359-397. https://doi.org/10.1080/1357650X.2020.1859526Test-retest reliability of an online chimeric faces task with single faces showing two emotions (Spearman r = .88), and Levy and colleagues' split-half reliability of .93.
- Speranza, B. E., Do, M., Hill, A. T., Donaldson, P. H., Enticott, P. G., & Kirkovski, M. (2025). Facial emotion processing hemispheric bias is weakly associated with handedness, autistic traits and biological sex, but not age. BMC Psychology, 13, 271. https://doi.org/10.1186/s40359-024-02218-2An online version: positions counterbalanced, attention checks with a smiling and a neutral face.
- DeBruine, L., & Jones, B. (2017). Face Research Lab London Set [Data set]. figshare. https://doi.org/10.6084/m9.figshare.5047666.v5
Source papers
- Levy J, Heller W, Banich MT, Burton LA (1983). Asymmetry of perception in free viewing of chimeric faces. Brain and Cognition, 2(4):404-419.Paradigm source, Adults
- DeBruine L, Jones B (2017). Face Research Lab London Set. figshare. Dataset. doi:10.6084/m9.figshare.5047666.v5Paradigm source, Adults
Questions
How long does the Chimeric Faces Task take?
About 5 to 7 minutes, as listed in the test library.
What device does a participant need?
Untimed test: runs on desktops, laptops and tablets. The browser must be Chrome, Edge, Firefox or Safari.
What scores does it produce?
Laterality Score, Left Smile Chosen, Upper Face Chosen, Pair Consistency, Choice Time Bias, Catch Pair Accuracy, Median Choice Time, Chimera Pairs Answered, Planned Chimera Pairs and Anticipations. Each session is also marked valid, needs review or invalid, with the reason.
How widely is the Chimeric Faces Task used in research?
23 papers from 2021 to 2025 name it in their title or abstract, down 36% compared with 2016 to 2020. That ranks it 321 of 395 test families in the ConductCognition test census (use grade E). Source: ConductCognition test census 0.14.0, counted 2 November 2026 from OpenAlex and ClinicalTrials.gov.
How much reliability evidence does the Chimeric Faces Task have?
In the published research, 3 papers report 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?
Number of pairs (64 (standard), 32). 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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