This document lists the sources used to justify Agentcha's challenge shapes. These sources guide defaults; they are not a proof that every human will fail or every automated solver will pass.
| Challenge | Research basis | How Agentcha applies it |
|---|---|---|
| Rapid enumeration | Subitizing has a small-item range, while larger sets require slower counting. | Ask for counts above the instant range and verify the numeric answer server-side. |
| RSVP stream | Attentional blink reduces second-target detection in rapid sequences. | Show a no-replay timed stream and ask for a typed observed token. |
| Visual search | Crowding and clutter reduce recognition and make search scale with field complexity. | Render dense visual fields as pixels rather than semantic DOM nodes. |
| Micro-world | Procedural semantic reasoning is easier to verify than to solve with a fixed shortcut. | Generate names, relationships, and a free-text answer from a larger answer space. |
| Change blindness | Flicker-style blank intervals make repeated scene changes hard to identify. | Generate two related scenes and ask for the changed position. |
| Sub-acuity text | Human acuity is bounded by minute-of-arc detail resolution. | Render small pixel-level codes and verify the typed string. |
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Trick, L. M., and Pylyshyn, Z. W. (1994). "Why are small and large numbers enumerated differently? A limited-capacity preattentive stage in vision." Psychological Review, 101(1), 80-102. DOI: 10.1037/0033-295X.101.1.80
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Raymond, J. E., Shapiro, K. L., and Arnell, K. M. (1992). "Temporary suppression of visual processing in an RSVP task: An attentional blink?" Journal of Experimental Psychology: Human Perception and Performance, 18(3), 849-860. DOI: 10.1037//0096-1523.18.3.849
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Whitney, D., and Levi, D. M. (2011). "Visual crowding: a fundamental limit on conscious perception and object recognition." Trends in Cognitive Sciences, 15(4), 160-168. DOI: 10.1016/j.tics.2011.02.005
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Rensink, R. A., O'Regan, J. K., and Clark, J. J. (1997). "To See or not to See: The Need for Attention to Perceive Changes in Scenes." Psychological Science, 8(5), 368-373. DOI: 10.1111/j.1467-9280.1997.tb00427.x
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Evans, J. M. (2006). "Standards for Visual Acuity." Prepared for the National Institute of Standards and Technology. URL: NIST PDF
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IETF Web Bot Authentication Working Group. The charter describes cryptographic authentication for automated clients, including search crawlers, web archivers, AI training crawlers, and AI agents. URL: IETF Datatracker
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Google reCAPTCHA v3 documentation. The server must verify the token and expected action on the backend, then use the returned score in site-specific risk handling. URL: Google Developers
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hCaptcha documentation. The browser returns a response token that the application verifies server-side with its secret. URL: hCaptcha Developer Guide
- Use typed answer spaces rather than four-option prompts where possible.
- Require a two-challenge chain before issuing a token.
- Keep the expected answer server-side.
- Consume challenges on answer submission.
- Keep protected content out of initial HTML.
- Use signed tokens with site key, action, expiry, and token ID.
- Treat browser telemetry as a signal, not a source of truth.
- Treat all browser-side obfuscation as friction only.
Agentcha is not a formal proof of personhood or agenthood. It is a source-available verification layer for agent-aware experiences. A determined operator with custom tooling can always move work outside the browser. The security boundary is the server-side token verification and content fetch pattern, not the modal UI alone.