CTRL-STEER: Closed-Loop Neuron Activation Control in Vision-Language-Action Models

Abhijith Babu, Ramneet Kaur, Nathaniel D. Bastian, Olivera Kotevska, Susmit Jha, Yanzhao Wu, Sumit Kumar Jha, Anirban Roy

Keywords: VLA, Steering, Control Theory

TL;DR: CTRL-STEER introduces a control-theoretic formulation of activation steering, treating neuron modulation as a feedback-regulated process that dynamically adapts to task execution

Abstract: Vision-Language-Action (VLA) models enable test-time behavioral steering via neuron-level interventions, but existing methods use fixed strengths and operate in open loop. This static modulation fails under evolving task dynamics, leading to overcorrection, oscillations, and reduced task success—especially for temporal attributes like speed. We propose CTRL-STEER, a control-theoretic framework that casts activation steering as closed-loop feedback with adaptive, time-varying interventions. Instead of assuming neurons encode temporal concepts, we steer along motion-aligned residual directions and regulate intervention magnitude via feedback. We instantiate this with both PID and reinforcement learning controllers that jointly optimize concept adherence and task success. Experiments on fine-tuned OpenVLA policies across four LIBERO suites show improved stability and a better steering–success trade-off over fixed-coefficient baselines, without retraining the base model.

Submission Number: 7