Automatic Detection of Generated Text is Easiest when Humans are Fooled
Written for the Research library (claude-opus-5-5) from the paper text, in our own words: the license "arXiv — non-exclusive license to distribute" does not allow redistributing the text itself. Original — arxiv.org/pdf/1911.00650
Summary
The paper asks why people and automatic classifiers disagree about whether a text came from a person or a language model, and how the decoding strategy shapes that gap. The authors generated excerpts with GPT-2 Large (774M parameters) using three sampling schemes: untruncated random sampling, top-k (k=40) and nucleus sampling (p=0.96). They paired these with human web text drawn from the same distribution as GPT-2's training data. For each scheme and several excerpt lengths, they fine-tuned BERT-based binary classifiers and also ran evaluations with trained human raters.
The main finding is an inverse relationship. Cutting off the low-probability tail, especially with top-k, makes output more convincing to readers. It also leaves statistical traces, such as a skewed token distribution, that classifiers detect easily. Automatic detectors beat humans in every setting, but they transferred poorly across decoding methods. The authors conclude that judging how human-like generated text is requires both human and automatic detectors.
Key points
- Per decoding method, the training set contains 250,000 generated excerpts paired with 250,000 webtext excerpts from the gpt-2-output-dataset. An extra 5,000 pairs are held out for validation and testing, and excerpts shorter than 192 WordPiece tokens are removed.
- Top-k output is the hardest for raters but the easiest for classifiers. Raters found untruncated and nucleus (p=0.96) samples equally hard, suggesting that p values well below the 0.92–0.98 range would be needed to seem noticeably more human.
- Human rater accuracy has a median of 74%, which is below the best discriminator. Even multi-sentence excerpts fooled expert raters more than 30% of the time.
- Random pairs of raters agreed on only 59% of excerpts, while raters and discriminators agreed on 61–70%. Humans tend to notice semantic errors such as topic drift and falsehoods, whereas classifiers pick up statistical artifacts.
- Classifiers trained on one strategy generalize poorly to another, but training on mixed data helps. Accuracy grows with excerpt length for both humans and machines. All experiments use English only.
Cited by
- Towards a Human-like Open-Domain Chatbot
- Fast-DetectGPT: Efficient Zero-Shot Detection of Machine-Generated Text via Conditional Probability Curvature
- On the Opportunities and Risks of Foundation Models
- Extracting Training Data from Large Language Models
- Paraphrasing evades detectors of AI-generated text, but retrieval is an effective defense
- DetectGPT: Zero-Shot Machine-Generated Text Detection using Probability Curvature
- MAUVE: Measuring the Gap Between Neural Text and Human Text using Divergence Frontiers
- Can AI-Generated Text be Reliably Detected?
- Beyond the Imitation Game: Quantifying and extrapolating the capabilities of language models
Cite
@misc{ippolito2019automatic,
title = {{Automatic Detection of Generated Text is Easiest when Humans are Fooled}},
author = {Ippolito, Daphne and Duckworth, Daniel and Callison-Burch, Chris and Eck, Douglas},
year = {2019},
doi = {10.48550/arxiv.1911.00650},
eprint = {1911.00650},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.1911.00650}
}References
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