Contextual contrast
Identical gray values can appear different when nearby luminance and texture change.
Truuts experiment
Perceptual CAPTCHA Experiment
A visual challenge based on contextual contrast and the way human vision locates the perceived center of an organic form.
About the experiment
The experiment asks a deliberately simple question: which shape appears darkest? Each organic form uses the same base gray, while its surrounding context changes how the visual system interprets it.
Validation focuses on the perceived heart of the chosen form rather than its geometric center. Reaction time and click position make the interaction observable without claiming to prove that a visitor is human.
This is a research prototype, not a production security system. A real verification flow would also require independent security evaluation and an accessible alternative for people with visual impairments.
Interactive demo
Choose the shape that appears darkest, then reveal the perceptual centers and compare visual judgment with geometric structure.
All three shapes use the same base gray.
Technical concepts
Perceptual center
The visually weighted center of an asymmetric form may not match its geometric midpoint.
Organic geometry
Irregular silhouettes reduce the usefulness of simplistic bounding boxes and perfect centroids.
Reaction time
Response timing offers a behavioral signal, although it cannot establish identity on its own.
Explainable inspection
Insight mode reveals the target zones after interaction so the mechanism remains observable.
Security limits
Perceptual novelty is a hypothesis to test, not a substitute for rate limits, abuse controls and accessibility.