The experiments described in Chapter 4 and in Appendix B used successive approximations to find the inertial amplitude at which participants crossed over between inertial and visual dominance (i.e., between having their perception of self-motion determined by inertial and visual cues). The inertial amplitude adjustments after each trial were made following the Parameter Estimation by Sequential Testing (PEST) procedure , which is a simple convergence algorithm developed for psychophysics experiments.
The PEST procedure obeys the following four rules:
The PEST procedure ends when the step size drops to a pre-determined amount. The estimate is the level called for by the last step.
In practice, the fact that each trial in the visual-inertial nulling experiments required a few minutes forced a fairly rapid convergence, which in turn required a final step size sufficient to allow for a rapid convergence (this was taken to be an amplitude of 5/sec in the experiment reported in Chapter 4, or 3/sec if the two conditions run in parallel would otherwise be tied). Hence, the subtleties of rules 3 and 4, above, rarely came into play.