Agent-based models of human operators rarely include explicit representations of the timing and accuracy of perception and action, although their accuracy is sometimes implicitly modelled by including random noise for observations and actions. In many situations though, the timing and accuracy of the person’s perception and action significantly influence their overall performance on a task. Recently many cognitive architectures have been extended to include perceptual/motor capabilities, making them embodied, and they have since been successfully used to test and compare interface designs. This paper describes the implementation of a similar perceptual/motor system that uses and extends the JACK agent language. The resulting embodied architecture has been used to compare GUIs representing telephones, but has been designed to interact with any mouse-driven Java interface. The results clearly indicate the impact of poor design on performance, with the agent taking longer to perform the task on the more poorly designed telephone. Initial comparisons with human data show a close match, and more detailed comparisons are underway.