Slip errors can have severe consequences but are notoriously difficult to reduce. Training, visual
cues and increasing motivation are generally not effective in eliminating these slips. Instead, the
approach this work takes is to identify which steps in a routine task are most error prone, so
that these can be designed out of device interactions. In particular, device- and task-oriented
steps are investigated. Device-oriented steps are "extra" steps imposed by the device that do
not directly contribute towards the task goal. Conversely, task-oriented steps directly bring the
user closer to their goal. The main hypothesis addressed in this work is that device-oriented
steps are more problematic than task-oriented ones.
The concepts of device- and task-oriented steps are investigated more closely, by analysing
the literature on routine action and mental representations of different steps. The core diff erence
between the steps is found to be how relevant a step is to the goal. This is further supported
by two qualitative studies.
A series of experimental studies investigates the cognitive mechanisms underlying device and
task-oriented steps. This is addressed through six experiments that address error rates, step
times, proportion of omissions and sensitivity to working memory load. Participants learned
one of three routine tasks, with several carefully controlled device- and task-oriented steps. The
results show that on device-oriented steps, error rates are higher, step times are longer, the
proportion of omissions is greater, and working memory load has an increased effect. These
findings support the hypothesis that activation levels are lower on device-oriented steps.
The thesis concludes that a step's relevance to the task goal plays an important role in
the occurrence of errors. This work has implications for both our understanding of routine
procedural action as well as the design of devices
