Noise-resilient collective order through temporal memory in self-propelled particles
Temporal memory can stabilise collective motion by filtering noisy local observations, but persistent information can also impede adaptation when the collective state changes. We investigate this competition in Vicsek-type systems using two distinct alignment rules: a finite buffer of past observations and a recursive update of an internal directional state. In both models, increasing effective memory shifts the loss of polar order to stronger noise and can restore ordered motion under conditions for which the corresponding memoryless Vicsek model is disordered. The stationary responses of the two models show an approximate correspondence when parameterised by a kernel-based effective memory, consistent with temporal averaging playing a common role in their ordering behaviour rather than from the details of the memory implementation. Their transient dynamics, however, are not determined by effective memory alone. Following a collective perturbation, recovery is fastest at an intermediate memory depth and becomes slower when outdated observations are retained too strongly. Temporal integration therefore produces a trade-off: deeper memory improves noise resilience, whereas excessive persistence reduces responsiveness. These results identify memory depth as a control parameter that separates the optimisation of stationary order from that of dynamical recovery in noisy active systems.