Target-directed head movements in a head-coupled virtual environment: Predicting the effects of lags using Fitts' law

Two experiments have investigated the effects of lag on discrete target-dir ected head movements in a virtual environment. Both the target and a head-s laved pointer (subjected to lag) were presented on a head-mounted display T arget-directed head movements in the presence of a constant time lag were s hown to obey Fitts' law (R-2 >.93). A previously reported interaction betwe en the effects of lag and the effects of index-of-difficulty on hand moveme nt time could not be found in head movement time when the target width was kept constant. Further experiments suggested that there is a significant in teraction between the effects of target width and lag but not between targe t distance and lag. A model predicting head movement strategy in the presen ce of lag is proposed to explain the experimental findings. This model pred icts, and experiments verified, that for a target width from 1 degrees to 8 degrees and a target distance range of 2.5 degrees to 30 degrees, the effe ct of lag (up to 267 ms) on target-directed head movement is independent of target distance but dependent on target width. Actual or potential applica tions of this research include the design of virtual control panel and its layout in a Virtual Reality simulator.