arXiv Machine Learning

Why Ghost Outputs Teach: A Kernel-Based Understanding of Subliminal Learning

The paper investigates subliminal learning (SL), where a student model learns downstream tasks by matching auxiliary outputs from a teacher without seeing task labels or original data. By deriving a chained cross‑task kernel, the authors link ghost‑output supervision to changes in task predictions via shared backbone representations. Their framework explains three empirical puzzles: a PSD transfer operator under shared initialization, a rank bottleneck set by ghost‑output dimensionality, and the superiority of high‑entropy synthetic inputs as broadband probes for maximizing kernel overlap.

arXiv AI
Sep 16

Verbalizing Subliminal Learning Effects Using Text Optimization

The paper introduces SALVE, a method that uses text optimization to uncover and verbalize subliminal learning effects in language models. By optimizing a soft prompt and converting it into a legible text prompt, SALVE can reliably recover the teacher model’s hidden traits that are transmitted through a distillation dataset. The authors demonstrate SALVE’s effectiveness across various scenarios, including mixed datasets, biased teacher activation, and preference‑selected data, thereby providing a tool for detecting hidden influences in model training.

By Nathan Hu, Sanmi Koyejo, Christopher Potts
arXiv Machine Learning
Oct 3

Localizing Transfer Between Memorization Tasks

The paper investigates how pre‑training on random input‑output mappings (memorization tasks) can transfer to downstream tasks. It discovers two unexpected patterns: equivalent transfer, where each pre‑training epoch saves roughly one fine‑tuning epoch, and non‑equivalent transfer, where pre‑training on a mismatched task can be more efficient than training directly on the downstream task. Ablation studies reveal that transfer consists of a trivial magnitude‑driven effect in the last layer and a non‑trivial structure‑driven effect linked to covariance in other layers.

By Yimiao Yu, Florentin Guth
arXiv Machine Learning
Sep 2

Subliminal Learning as Trait-Direction Drift: A Mechanism and Targeted Control under SFT Distillation

The paper investigates subliminal learning, where hidden traits from a teacher model are transferred to a student during distillation. It introduces trait‑direction drift as the underlying mechanism, showing that biased generation creates measurable preference gaps that accumulate into behavioral transfer during fine‑tuning. The authors propose probe‑space corridor regularization, a targeted defense that constrains drift along a calibrated trait direction, significantly reducing hidden‑trait transfer while maintaining task performance.

By Zhixuan Liu, Zhichen Dong, Yuyu Fan, Xiangtian Li, Chao Yang