# Where Does the Beam Emerge?

A straight laser beam enters an opaque barrier at an acute angle. Place your target where you think the beam will exit on the opposite side, then fire to measure the trajectory distortion created by your visual cortex.

[Open the interactive game](https://mariuscomper.uk/unde-iese-raza/en/)

## How it works

1. Each round presents a laser beam striking an opaque wall at a defined angle.
2. Tap or drag the right rail cursor to align your target where you expect the line to emerge.
3. Tap "Fire beam" (or press Spacebar). The barrier turns translucent as the physical beam cuts through on the true Euclidean path.
4. After five rounds, you receive your mean absolute error in millimeters, angular bias, and a Poggendorff diagnosis.

## Neural mechanism

Primary visual cortex (area V1) computes orientations using dedicated neuronal columns. When an oblique transversal meets a vertical boundary, active neurons inhibit each other horizontally. This lateral inhibition expands the perceived acute angle by 2 to 5 degrees, pulling the perceived exit downward.

Design and implementation: Marius Comper, September 2026.