Line Bisection Bias

In the Line Bisection Task, you are asked to click the subjective midpoint of horizontal lines of varying lengths. This task assesses spatial attention bias (often called 'pseudoneglect'), where healthy individuals typically show a slight leftward bias. This online demonstration is for educational and self-reflection purposes only — it is not a screening or diagnostic tool for hemispatial neglect.

For each trial, click where you think the exact center of the line is. Line lengths will vary across trials. Summary metrics will be shown after completing all trials, and data can be exported.

Frequently Asked Questions

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What does this task measure?

It evaluates your left/right spatial bias across different line lengths by asking you to click the 'subjective midpoint'.

How to proceed?

In each trial, click the location you perceive as the center of the line. View summary results after completing all trials.

How are results calculated?

Your average bias (in pixels) and standard deviation are calculated for each line length, reflecting the magnitude and stability of your bias.

Can I export data?

Yes. You can save a JSON file or download a CSV containing metrics and all trial records.

Show Details

Implementation

This experiment presents horizontal lines of three lengths (300, 360, and 420 px), 10 trials each. On every trial you click where you perceive the line's center, and the deviation between your click and the true midpoint is recorded in pixels. All computation happens entirely on the client side.

Experiment Introduction

The Line Bisection experiment demonstrates how spatial attention can be biased: when asked to judge a line's midpoint, most healthy people place it slightly to the left of the true center — a phenomenon known as 'pseudoneglect'. Comparing your average bias across line lengths lets you observe this subtle perceptual asymmetry in yourself.

Metrics

For each line length, the experiment reports the mean signed deviation of your clicks from the true midpoint (in pixels; negative = left of center) and its standard deviation, plus per-trial records. All data can be exported to JSON or CSV.

References

Schenkenberg, T., Bradford, D. C., & Ajax, E. T. (1980). Line bisection and unilateral visual neglect in patients with neurologic impairment. Neurology, 30(5), 509-517. 10.1212/WNL.30.5.509
Jewell, G., & McCourt, M. E. (2000). Pseudoneglect: A review and meta-analysis of performance factors in line bisection. Neuropsychologia, 38(1), 93-110.
Bowers, D., & Heilman, K. M. (1980). Pseudoneglect: Effects of hemispace on a tactile line bisection task. Neuropsychologia, 18(4-5), 491-498. 10.1016/0028-3932(80)90151-7

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About This Experiment

This experiment is an educational adaptation for demonstration purposes. It is not a clinical diagnostic tool. Results reflect your performance in this specific session and should not be interpreted as an assessment of your cognitive abilities.

Data Privacy

Your experiment data is processed and stored locally in your browser. No data is uploaded to any server unless you explicitly export it.