Rethinking Kalman Filters for Motor Brain-Machine Interface: The Fundamental Limitations and A Perspective Shift

The Kalman filter has been introduced to the motor brain-machine interface (BMI) field for over 20 years and remains one of the most widely used models due to its simple and intuitive nature. However, this paper demonstrates that the application of Kalman filters in the BMI field violates the models own assumptions and numerous neuroscience principles, resulting in six critical limitations: (1) the observation matrix mapping from kinematics to neural activity causes individual neurons to be modeled independently, ignoring neural population activity; aligned kinematic and neural activity sequences fail to capture preparatory information; (3) the presence of behaviorally irrelevant neural activity causes observation weights to be excessively underestimated; (4) noise in the observation matrix renders posterior covariance estimates biased; (5) Kalman gain computation in observation space leads to repeated noise accumulation and (6) computational inefficiency. All these problems can be resolved through a simple perspective shift: separating the decoder from the Kalman filter and treating its predicted kinematics as the Kalman filters observation rather than neural activity. Experiments conducted on CRCNS-recorded monkey dorsal premotor area and primary motor signals performing computer cursor control tasks validate the existence of the six limitations and their violations of neuroscience principles, while demonstrating the superiority of the improved Kalman filter across all evaluated metrics.