How practice produces suboptimal heuristics that render backup instruments ineffective

The operation of machines typically requires attention to instruments that signal the state of the machine. One safeguard against primary instrument malfunction is to provide backup instruments, but this works only if the operators react to malfunction by switching attention to the backups. Little is known about the effect of negative outcomes or feedback on allocation of attention to backup instruments. Four experiments demonstrated that prior practice causes operators of a simulated machine to adapt to instrument malfunction by changing to a suboptimal decision rule rather than by reallocating attention to a different set of instruments. This fallacy appears linked to the operators' failures to notice feedback that they should switch during the simulations and operators' failures to correctly interpret outcome feedback following the simulations. The results raise theoretical questions and warn interface designers not to overrate backup instruments.