Attention
Contrast Surround Task
Also called: contrast-contrast effect, contrast contrast task, CCE, center-surround contrast suppression, visual surround suppression
Measure how surrounding stripes change the contrast people see in a central patch, using judgments with and without the surround.
4-6 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
- 6
- Evidence grade
- D
- Registered clinical studies
- 0
What it measures
Judge which of two striped patches has stronger contrast. The first patch appears alone or inside a high-contrast ring. Scores how the ring shifts the contrast that looks equal, relative to the no-surround baseline.
Constructs
- Contextual contrast perception
- Visual gain control
- Surround suppression
Research uses
- Group research on contextual visual processing
- Research on differences in contrast perception
How the paradigm works
A high-contrast surround can make the contrast of a central patch look weaker. This task compares the central patch with a second patch and estimates the contrast that looks equal, with and without the surround. The difference measures the contextual shift in apparent contrast.
More about the paradigm
Our generated vertical gratings use a 40% reference and a 95% surround. The reference appears for 500 ms, followed by a 100 ms blank and a 500 ms comparison at one of seven fixed contrasts from 10% to 70%. Participants then choose first or second, with no time limit. The standard session has 92 test comparisons, including 8 clear checks without a surround, after 6 practice comparisons.
A cumulative Gaussian is fitted separately to each condition. The primary score is the no-surround match minus the surround match in nominal contrast percentage points; positive values indicate suppression. Unbounded estimates remain missing. Screens differ in luminance response, size and timing; no calibration is required. This research task provides no clinical classification.
Scores
- Surround Shift%
- Baseline equal-contrast match minus surround match, in nominal contrast percentage points.
- Positive means the ring reduced apparent center contrast; no better direction
- Match Without Surround%
- Comparison contrast judged equal to the 40% reference without a surround.
- Informational
- Match With Surround%
- Comparison contrast judged equal to the reference with a 95% surround.
- Informational
- Spread Without Surround%
- Half the fitted 25% to 75% response span without a surround. Null for a step narrower than the levels can resolve.
- Smaller means finer contrast judgments
- Spread With Surround%
- Half the fitted 25% to 75% response span with a surround.
- Informational
- Check Accuracy%
- Share correct on at least 4 usable no-surround checks at 10% or 70%.
- Below 0.5 invalidates; below 0.75 is flagged
- Median Answer Timems
- Median time from the second patch disappearing to the answer.
- Informational
- Anticipationscount
- Answers under 100 ms, excluded from the estimates.
- Lower is better
- Early Key Pressescount
- Arrow keys pressed before both patches disappeared, ignored.
- Informational
- Frame Intervalms
- Median measured screen-frame interval.
- About 16.7 ms at 60 Hz
- Dropped Frames%
- Share of expected display frames skipped.
- Above 0.05 is flagged
- Sequence Durationms
- Median measured duration of both patches and the intervening gap.
- About 1100 ms
- Completed Trialstrials
- Answered test comparisons in the selected run.
- Fewer than planned is flagged
- Planned Trialstrials
- Number of planned test comparisons.
- Informational
Use and evidence
6 papers from 2021 to 2025 name this task in their title or abstract. That ranks it 468 of 495 test families in our census. See the counts for every test.
Show the numbers
| Year | Papers |
|---|---|
| 2025 | 0 |
| 2024 | 0 |
| 2023 | 4 |
| 2022 | 0 |
| 2021 | 2 |
| 2020 | 1 |
| 2019 | 2 |
| 2018 | 1 |
| 2017 | 3 |
| 2016 | 2 |
| 2015 | 2 |
| 2014 | 2 |
| 2013 | 2 |
| 2012 | 4 |
| 2011 | 6 |
| 2010 | 1 |
| 2009 | 0 |
| 2008 | 1 |
| 2007 | 0 |
| 2006 | 0 |
| 2005 | 0 |
| 2004 | 0 |
| 2003 | 0 |
| 2002 | 0 |
| 2001 | 1 |
| 2000 | 0 |
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
- 2
- Registered clinical studies using it as an outcome
- 0
Note on the counts: Generated gratings and fixed comparison levels; nominal sRGB contrast, no calibration or clinical classification..
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.
- Patches
- Original vertical gratings: 30 px center radius, 3 px gap and 100 px outer surround radius, with a 10 px stripe cycle. Reference contrast 40%; surround 95%, or absent. Nominal sRGB luminance, background code 187.
- Timing
- 500 ms fixation, 500 ms reference, 100 ms blank, 500 ms comparison. Respond after the second patch disappears. The measured duration of each part is saved.
- Comparison levels
- 10, 20, 30, 40, 50, 60 and 70% contrast, each 6 times in each surround condition. The 4 to 12 repeats setting gives 64 to 176 tests including checks; standard 92.
- Checks and practice
- 8 clear checks without a surround, 4 at 10% and 4 at 70%. Before testing, 6 no-surround comparisons with feedback for 1000 ms. Short breaks every 32 tests.
- Response
- Left arrow or First for the first patch; right arrow or Second for the second. No response deadline. Compare the central patch, not its surrounding ring.
- Scores
- No-surround minus surround equal-contrast match, from cumulative Gaussian fits, in nominal contrast percentage points. Separate matches and spreads, check accuracy and timing are also reported. Answers under 100 ms leave the estimates.
Our gratings replace the source’s filtered noise, and fixed comparison levels replace its staircase. Screens differ; contrast values assume the sRGB luminance curve. Compare sessions on similar screens. No calibration or clinical classification.
Quality checks
Each session is marked valid, needs review or invalid, with the reason, before you see its scores.
Scored rows: contrast_surround_test from the scored run, one first-or-second answer after both patches disappear. Only the clear no-surround checks are graded for validity: with at least 4 usable checks, below half correct invalidates and below three quarters is flagged. Unbounded matches, incomplete runs and poor display timing are flagged. Responses under 100 ms follow the timed-test rule.
Why these rules
A high-contrast surround changes apparent central contrast, so treating every physical contrast mismatch as an error would discard the effect being measured. Clear checks without a surround test the response rule. Missing or unbounded matches remain missing rather than being assigned zero suppression.
No percentile. Scores and quality flags only.
Running this test
Settings you can change
| Setting | Standard | Allowed |
|---|---|---|
| Trials at each comparison contrast | 6 | 4 to 12 |
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 Contrast Surround Task in a web browser (ConductCognition task version 1.0.0, scoring version 1.0.0; Dakin, Carlin and Hemsley, 2005; Barch and colleagues, 2012), with the standard settings (trials at each comparison contrast: 6). The main score was surround shift (baseline equal-contrast match minus surround match, in nominal contrast percentage points).
ConductCognition versions: task version 1.0.0, scoring version 1.0.0. Every export records the versions each session used, for a methods section.
- Barch, D. M., Carter, C. S., Dakin, S. C., Gold, J., Luck, S. J., MacDonald, A., Ragland, J. D., Silverstein, S., & Strauss, M. E. (2012). The clinical translation of a measure of gain control: The contrast-contrast effect task. Schizophrenia Bulletin, 38(1), 135-143. https://doi.org/10.1093/schbul/sbr154Sequential contrast comparisons, a no-surround baseline, catch trials and cumulative Gaussian fits. Published online in 2011; volume 38 is the 2012 issue.
- Dakin, S., Carlin, P., & Hemsley, D. (2005). Weak suppression of visual context in chronic schizophrenia. Current Biology, 15(20), R822-R824. https://doi.org/10.1016/j.cub.2005.10.015Contrast matching with and without a surround measures the influence of visual context.
Source papers
- Barch, D. M., Carter, C. S., Dakin, S. C., Gold, J., Luck, S. J., MacDonald, A., Ragland, J. D., Silverstein, S., & Strauss, M. E. (2012). The clinical translation of a measure of gain control: The contrast-contrast effect task. Schizophrenia Bulletin, 38(1), 135-143.Paradigm source, Adults
Questions
How long does the Contrast Surround Task take?
About 4 to 6 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?
Surround Shift, Match Without Surround, Match With Surround, Spread Without Surround, Spread With Surround, Check Accuracy, Median Answer Time, Anticipations, Early Key Presses, Frame Interval, Dropped Frames, Sequence Duration, Completed Trials and Planned Trials. Each session is also marked valid, needs review or invalid, with the reason.
How widely is the Contrast Surround Task used in research?
6 papers from 2021 to 2025 name it in their title or abstract. That ranks it 468 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 Contrast Surround 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?
Trials at each comparison contrast (4 to 12). 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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