SURE: Support-Conditioned Unreliability-Aware Residual Exteroception for Graceful Degradation in Humanoid Locomotion

Visual terrain perception helps humanoids traverse complex terrain, but erroneous or stale elevation maps can misdirect foot placement and whole-body motion. Controllers therefore need to determine when to stop relying on map guidance while maintaining basic locomotion after a mismatch. We propose SURE (Support-Conditioned Unreliability-Aware Residual Exteroception), a visual-residual control method based on physical consistency between vision and proprioception. SURE adds a visual residual to a blind base policy driven by proprioception, providing terrain-dependent action corrections. To decide when to use these corrections, it infers foot support and collision states from proprioception and checks them against local map geometry. Vertical checks compare supporting-foot height with mapped terrain height, while horizontal checks compare foot-front obstruction with mapped obstacle geometry. Physical contradictions prompt residual withdrawal, leaving the blind base policy in control. Subsequent foot placements must pass support verification before visual corrections resume. Simulations show that SURE preserves complex-terrain locomotion under nominal vision. Under local geometric mismatch and map delay, SURE improves walking success relative to the same policy with the visual residual always enabled. Restoration ablations show that map-based support verification improves completion beyond proprioceptive recontact under delay and height drift. Real-robot experiments further demonstrate terrain traversal with omitted obstacles or delayed maps. These results show that physically grounded residual control reconciles terrain adaptation under nominal vision with basic locomotion after perceptual mismatch, providing interpretable graceful degradation.