A human-machine-interaction (HMI) model is developed for the human operator (HO) performing five simultaneous tasks and characterized by a strategy function. Five levels of total machine-initiated baud rate (B(IN)) are generated by the multi-attribute task battery (MATB) and five HO baud rates (B(O)) are then recorded. Total baud ratio (B ) is defined as the ratio of B(O) to B(IN). Results indicate that with increasing B(IN) levels: (1) there is an overall increase in B(O), and (2) there is an overall decrease in B . These results are due to a decreasing HMI performance and divergence of the strategy function from a unity model paradigm.