  Deep neural networks are used in many state-of-the-art systems for machine
perception. Once a network is trained to do a specific task, e.g., bird
classification, it cannot easily be trained to do new tasks, e.g.,
incrementally learning to recognize additional bird species or learning an
entirely different task such as flower recognition. When new tasks are added,
typical deep neural networks are prone to catastrophically forgetting previous
tasks. Networks that are capable of assimilating new information incrementally,
much like how humans form new memories over time, will be more efficient than
re-training the model from scratch each time a new task needs to be learned.
There have been multiple attempts to develop schemes that mitigate catastrophic
forgetting, but these methods have not been directly compared, the tests used
to evaluate them vary considerably, and these methods have only been evaluated
on small-scale problems (e.g., MNIST). In this paper, we introduce new metrics
and benchmarks for directly comparing five different mechanisms designed to
mitigate catastrophic forgetting in neural networks: regularization,
ensembling, rehearsal, dual-memory, and sparse-coding. Our experiments on
real-world images and sounds show that the mechanism(s) that are critical for
optimal performance vary based on the incremental training paradigm and type of
data being used, but they all demonstrate that the catastrophic forgetting
problem has yet to be solved.
