What is Perplexity and Burstiness?
TL;DR
Two signals AI detectors use to tell AI from human text: how predictable words are (perplexity) and how varied sentences are (burstiness).
Perplexity and Burstiness: Definition & Explanation
Perplexity and burstiness are the representative signals AI detectors use to estimate whether text was AI-generated or human-written. Perplexity measures how predictable the next word is; lower values mean safe, predictable words are lined up. AI tends to pick high-probability words, so it runs low, while humans use surprising words and run high. Burstiness measures variation in sentence length and complexity; humans mix long and short sentences and run high, whereas AI tends to be uniform and run low. Detectors combine the two, but judgments are not certain: people who write in formulaic styles can be falsely flagged as AI, and tuned AI text can slip through. AI humanizers restructure text to move these signals toward the human side.