Mental representations of obligatory and prohibitory traffic signs

Every traffic sign conveys a single proposition about traffic conditions. Drivers must integrate this proposition with their goals and other known facts to decide on an appropriate action in what amounts to a deduction task. For example, imagine that you are driving a car and you want to turn right at an intersection but there is a 'no right turn' sign. You have to assess the options and make a decision (reach a conclusion). Theoretical accounts from research about reasoning can be applied to how we understand traffic signs and make inferences from them. This study includes two experiments that analysed how people decide whether a situation is allowed or not, taking into account the information provided by one sign--obligatory or prohibitory--or two signs--two obligatory or two prohibitory signs. The number of signs, that is, the complexity of the driving scene, was a key factor in this study. The two experiments differ in the presentation format of the two-sign experimental condition. In the first experiment, the signs were presented as two isolated signs. In the second experiment, the two signs were embedded in one. Equivalent results were found whether two isolated signs or two embedded signs were shown. When an obligatory sign was used at the junction, faster responses were obtained for allowed manoeuvres than for those not allowed. When a prohibitory sign was used, the results were the opposite. However, the advantage of prohibitory signs in the not-allowed situation was not replicated when people had to collect information from two prohibitory signs. Results showed that people integrate two obligatory sign messages--informing where one can go--more easily than two prohibitory sign messages--informing where not to go. Therefore, it could be said that each traffic sign elicits an internal mental model elaboration in which forbidden actions are explicitly labelled by means of attached "mental footnotes" indicating the epistemic status of "prohibitory information."