Efficacy of modified backpropagation and optimisation methods on a real-world medical problem

A wide range of modifications to the backpropagation (BP) algorithm, motivated by heuristic arguments and optimisation theory, has been examined on a real-world medical signal classification problem. The method of choice depends both upon the nature of the learning task and whether one wants to optimise learning for speed or generalisation. It was found that, comparatively, standard BP was sufficiently fast and provided good generalisation when the task was to learn the training set within a given error tolerance. However, if the task was to find the global minimum, then standard BP failed to do so within 100000 iterations, but first order methods which adapt the stepsize were as fast as, if not faster than, conjugate gradient and quasi-Newton methods. Second order methods required the same amount of fine tuning of line search and restart parameters as did the first order methods of their parameters in order to achieve optimum performance.