An adaptive filter algorithm used to remove noise such as ocular artefacts from electroencephalograph (EEG) signals, is controlled during high noise spikes which may cause the adaptive filter algorithm to become unstable. A signal from at least one sensor (e.g. an ocular sensor) is received 202, and from this signal it is determined whether the adaptive filter algorithm is subject to becoming unstable. The operation of the filter algorithm is suspended 210 while the filter algorithm is subject to becoming unstable. The stability of the filter algorithm is determined by calculating z-scores 206 - if the z-score of the ocular signal exceeds given threshold 208 the adaptive filter algorithm is considered to be subject to instability, and the algorithm is suspended 210.
Statistical control of adaptive ocular filter stability