Mixed signals: stimulus-response compatibility and car indicator light configuration

The amber indicator lights on cars are designed to enable road users to efficiently predict the driver's next manoeuvre. Among other factors (e.g. luminance), the spatial configuration of these lights facilitates their interpretation (e.g. the right indicator flashes for right turns). However, several modern models of car confound this relationship by placing indicators medially relative to the headlights. Hence, the left indicator is placed to the right of the left headlight, for example. In two computer-based experiments, the object-based incompatibility that arises from this latter configuration resulted in slower, more erroneous responses to the indicated direction than for the standard configuration. These data act as a reminder to car designers that indicators, which are inherently a safety feature, should be designed with how fluently they can be processed by the human visual system in mind and not just for aesthetic appeal.