Adaptation Asymmetry in Manual Tracking

A theory of manual adaptive control requires an understanding of the mechanisms by which human op erators alter their control strategies in response to changes in control conditions Here we show that signi cant asym metries in adaptation occur in a manual tracking task when well trained subjects are exposed to situations in which track preview lag of the controlled system or track bandwidth gradually change We analyzed the experimental data using our recently developed recursive system identi cation algo rithm which not only estimates non stationary linear model coe cients but also time varying delay time We show that daptation strongly depends on whether the task becomes eas ier or more di cult as a result of changing conditions Sub jects were not always inclined to improve their strategy when tracking di culty gradually decreases as a result of changing conditions When the task gradually became more di cult subjects seemed predisposed to maintain their current strat egy rather than switching to a more e ective strategy par ticlularly when switching required an increased work load or attentional demand The observed adaptation asymme tries indicate that tracking performance can not be predicted based on momentary task conditions alone To establish a model of adaptation mechanisms and its driving forces the recent history of changes in tracking conditions needs to be considered We attribute the observed asymmetries to a per formance judgment process which triggers adaptation when perceived performance falls outside a subjective range that depends strongly on the recent history of tracking conditions