A Dominant Self-Conditioning Direction Drives Repetition in Unconditional Continuous Diffusion Language Models

Abstract

Continuous diffusion language models offer an alternative to autoregressive generation, but their generations may suffer from repetition. We find that unconditional generations from ELF, a recent family of continuous diffusion language models, are more repetitive than human text, while Gen-PPL, a common likelihood-based metric, gives lower perplexity to repetitive generations and can conceal this problem while biasing quality evaluation. Our analysis links this behavior to a self-conditioning feedback loop in which clean-embedding predictions are repeatedly carried into subsequent denoising steps, driving representations toward an effectively one-dimensional contractive attractor associated with repetition. Based on this mechanism, we introduce Attractor-Contrast-Escape (ACE), a training-free inference-time intervention that estimates a repetition direction by contrasting denoising paths trapped in repetition with paths relatively free of repetition and subtracts it from the self-conditioning feedback during denoising. Using a direction estimated only once on ELF-B, ACE reduces mean 4-gram self-repetition rate from 7.28% to 4.48%, while retaining competitive results on several text-quality metrics beyond Gen-PPL. The direction remains effective across ELF sizes and inference configurations, and ACE also generalizes to other unconditional self-conditioned continuous diffusion language models. These results identify self-conditioning feedback as a source of repetition in continuous diffusion language models and show that ACE can directly mitigate this repetition during inference.