# Through the Tunnel: can you catch the exit?

Track the speed along the launch runway. Inside the tunnel, the mark vanishes completely. Press the key or tap the track at the exact instant you predict it reaches the exit line. The experiment tests five attempts across varying speeds, reveals each signed offset, and calculates mean absolute error, best attempt, and directional bias.

[Open the interactive experiment](https://mariuscomper.uk/prin-tunel/en/)

## How it works

1. The mark moves along an open launch window to allow your visual system to lock onto its velocity.
2. At 28% of the runway, the mark enters an opaque chamber and disappears.
3. Press Space, Enter, or tap the screen when you predict the mark reaches the 90% gate.
4. The shutter opens instantly, freezing the physical position of the mark and displaying the millisecond delta.
5. After five rounds of varied speed, receive the full kinematic profile of your internal simulation.

## How the tunnel measures internal velocity

When a moving object slides behind an occluder, vision cuts out, but the nervous system continues running an internal kinematic simulation. In perceptual science, this ability is studied as time-to-contact estimation.

Decades of psychophysical findings show that observers do not rely on passive counting. Instead, the brain projects the trajectory forward with simulated momentum. Under high visual speeds or elevated focus, people tend to jump the gun (anticipatory bias); under prolonged occlusion, internal simulations often lag, producing representational deceleration.

This instrument records the signed difference between your trigger press and the physical arrival of the mark at the 90% gate line. Results reflect personal perceptual calibration as well as the display and input latency of your current hardware.

Design and implementation: Marius Comper, 3 September 2026.