Table 1 Summary of previous COACH systems.

Version 1

Pattern wristband worn by the user

Neural networks interacting with a hard-coded taxonomy

Audio prompts, with one prompt for each step

Version 2

Using background subtraction to isolate the user's hands. Tracking of hands and task objects (i.e. soap and towel) using a preset colour model.

Fully observable Markov decision process (MDP). This technique assumes the world is fully observable; it does not take into account hidden variables, such as user responsiveness.

Audio prompts with three levels of assistance (minimal, moderate, and maximal) for each step.

Version 3 (system presented in this paper)

Colour based flocking.

[Belief monitoring system & policy] Partially observable Markov decision process (POMDP). This model takes into account hidden variables and is able to make decisions in conditions of uncertainty.

Audio and audio-video prompts with three levels of assistance (minimal, maximal, and maximal + video demonstration) for each step. Encouragement and a reminder regarding the activity the user is attempting added. Professional actor recorded prompts.