  Measuring brain activity with electroencephalography (EEG) is mature enough
to assess mental states. Combined with existing methods, such tool can be used
to strengthen the understanding of user experience. We contribute a set of
methods to estimate continuously the user's mental workload, attention and
recognition of interaction errors during different interaction tasks. We
validate these measures on a controlled virtual environment and show how they
can be used to compare different interaction techniques or devices, by
comparing here a keyboard and a touch-based interface. Thanks to such a
framework, EEG becomes a promising method to improve the overall usability of
complex computer systems.
