By eye.
Without a ruler, set square or compass, how accurately can you find the middle of a line, the center of a circle or an exact right angle?
Original study
- Jewell, G., & McCourt, M. E. (2000). Pseudoneglect: A review and meta-analysis of performance factors in line bisection tasks. Neuropsychologia, 38(1), 93–110. Source
- Bowers, D., & Heilman, K. M. (1980). Pseudoneglect: Effects of hemispace on a tactile line bisection task. Neuropsychologia, 18(4–5), 491–498. Source
- Learmonth, G., Gallagher, A., Gibson, J., Thut, G., & Harvey, M. (2015). Intra- and inter-task reliability of spatial attention measures in pseudoneglect. PLoS ONE, 10(9), e0138379. Source
- Friedrich, T. E., Hunter, P. V., & Elias, L. J. (2018). The trajectory of pseudoneglect in adults: A systematic review. Neuropsychology Review, 28(4), 436–452. Source
- Gray, R., & Regan, D. (1996). Accuracy of reproducing angles: Is a right angle special? Perception, 25(5), 531–542. Source
- Whitaker, D., McGraw, P. V., Pacey, I., & Barrett, B. T. (1996). Centroid analysis predicts visual localization of first- and second-order stimuli. Vision Research, 36(18), 2957–2970. Source
- Appelle, S. (1972). Perception and discrimination as a function of stimulus orientation: The "oblique effect" in man and animals. Psychological Bulletin, 78(4), 266–278. Source
Our adaptation
An eye-judgment game of line bisection (Jewell and McCourt, 2000) and five geometry tasks. All tasks are drawn on a paper-colored square field. In round 1 the middle of four horizontal lines is found (the starting point is on the left twice and on the right twice); later rounds each hold one task: center of a circle, right angle, fourth corner of a square, parallel line and centroid of a triangle. Lines given in the right-angle and parallel tasks are oblique.
Differences from the original study
- Four bisections are too few to establish a personal left-right bias.
- Mouse and touchscreen require different movements.
Measured variables
The columns of the open data file. List fields are expanded into numbered columns (for example rt_60, est_3); JSON columns contain only numbers and fixed stimulus names.
| Column | Type | Description |
|---|---|---|
d | JSON | Answers: [[task, geometry g1…g6, answer x, answer y, start x, start y, time in ms] × 9] (unit square field, y down). |
pts_1 | number | Round score (0–10; mean of four answers in the bisection round). (item 1) |
pts_2 | number | Round score (0–10; mean of four answers in the bisection round). (item 2) |
pts_3 | number | Round score (0–10; mean of four answers in the bisection round). (item 3) |
pts_4 | number | Round score (0–10; mean of four answers in the bisection round). (item 4) |
pts_5 | number | Round score (0–10; mean of four answers in the bisection round). (item 5) |
pts_6 | number | Round score (0–10; mean of four answers in the bisection round). (item 6) |
points | number | Total score (0–60). |
bisect_bias | number | Bisection bias (% of line length; negative = left). |
task_err_1 | number | Mean error per task: task_err_1 bisection (%), _2 right angle (°), _3 square (% of side), _4 center (% of radius), _5 parallel (°), _6 centroid (%). (item 1) |
task_err_2 | number | Mean error per task: task_err_1 bisection (%), _2 right angle (°), _3 square (% of side), _4 center (% of radius), _5 parallel (°), _6 centroid (%). (item 2) |
task_err_3 | number | Mean error per task: task_err_1 bisection (%), _2 right angle (°), _3 square (% of side), _4 center (% of radius), _5 parallel (°), _6 centroid (%). (item 3) |
task_err_4 | number | Mean error per task: task_err_1 bisection (%), _2 right angle (°), _3 square (% of side), _4 center (% of radius), _5 parallel (°), _6 centroid (%). (item 4) |
task_err_5 | number | Mean error per task: task_err_1 bisection (%), _2 right angle (°), _3 square (% of side), _4 center (% of radius), _5 parallel (°), _6 centroid (%). (item 5) |
task_err_6 | number | Mean error per task: task_err_1 bisection (%), _2 right angle (°), _3 square (% of side), _4 center (% of radius), _5 parallel (°), _6 centroid (%). (item 6) |
Columns present in every file (14)
row_id | string | Row code. Regenerated at random in every release; it does not identify a person and cannot be matched across releases or experiments. |
experiment | string | Short name of the experiment (URL slug). |
experiment_version | integer | Version of the answer format. For experiments whose format changed, only the current format is published. |
date | YYYY-MM-DD | YYYY-Www | YYYY-MM | Day the answer was given (Istanbul time). If fewer than 5 answers share the same day, language and device, it is coarsened to the ISO week, and to the month if that is still too few. |
date_precision | day | week | month | Precision of the date column. |
lang | tr | en | (boş) | Interface language. Language recording started in the first week of October 2026; for earlier answers it is known only in experiments whose stimuli depend on the language, and empty otherwise. |
device | desktop | mobile | tablet | (boş) | Device class reported by the browser (class only; browser details are neither stored here nor published). |
source | site | embed | Where the answer came from: the balabs site or the experiment embedded on another site. The embedding site is not published. |
mode | free | daily | challenge | race | session | (boş) | Play mode in scored experiments: free play, daily round, challenge, race room, experiment session. Empty for unscored experiments and for older answers that did not store it. |
color_vision | normal | rg | by | contrast | (boş) | In color-based experiments, the color vision mode the participant chose: normal, red-green, blue-yellow or high contrast. Stimuli are generated along different axes per mode, so compare within a mode. Empty for other experiments. |
first_play | 1 | Every row is a participant’s first play of this experiment (always 1). Replays are stored only as leaderboard scores and are not part of the open data. |
seen_before | yes | no | unsure | (boş) | Participant’s own report of whether they had seen this experiment or its known answer before (in experiments that ask). |
duration_s | number | Time from the start of the experiment to submitting the answer, in seconds (measured in the browser, 0.1 s). |
play_score | number | Leaderboard score of the first play (scored experiments; defined on the method card). Empty for unscored experiments. |
Exclusion criteria
The server checks that the task order follows the plan and that the geometry is valid, and computes errors itself.
- Only each participant's first answer to this experiment; replays are not included.
- Simulated rows, bots, banned and sample accounts are not included.
- Answers before 3 October 2026 are not included (the first day the open data notice was live).
Scoring
Leaderboard score: total score (0–60); higher is better.
Leaderboard measure: eyeballing (higher is better). The play_score column in the open data is this score for the first play.
Version notes
- October 2026
The interface language (lang) started being stored with each answer; for earlier answers it is known only in experiments whose stimuli depend on the language, and empty otherwise.