Interaction of Movement Difficulty due to the Misalignment Effect and Response Latency

Abstract

In previous reports we measured and analyzed the Misalignment Effect Function, a function describing the decrement in human performance due to rotation between operators’ display and control axes. This prior work allowed us to determine difficulty-matched sets of rotations for a generalized 3D Fitts-like movement task. We consequently are now able to study the interaction of system latency and movement difficulty in a highly generalized way in a virtual telerobotic environment using wide variety of conditions and targets. Our targets are located on a spherical shell near our participants’ starting point in a high dynamic fidelity virtual environment. Analysis of participants’ ability to make movements to these targets has revealed a purely multiplicative interaction between control latency and task difficulty. Interestingly, we show that this the observed interaction supports work on Fitts’ Law by E.R. Hoffmann and that it depends upon accounting for an internal human processing latency of ~250 ms. Our data suggest that the interaction varies nonlinearly due to task difficulty in a manner consistent with Hoffmann’s results. We propose a descriptive equation to reflect the observed interaction that can be seen as a spatiotemporal generalization of Fitts’ Law. Our results provide a basis for generalizing latency requirements for reference tasks that may be varied in difficulty in a manner analogous to the Fitts’ Index of Difficulty.