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Max Brake Force as a Measure of Perceived Urgency in a Driving Context

Participants drove a simulated vehicle while completing an n-back task of high or low cognitive demand. Concurrently, they responded via brake press to signals presented in either a single modality (auditory, visual or tactile) or a bimodal combination. Participants were asked to indicate the perceived urgency of each signal by adjusting the force applied in their brake response. Signals were designed to be of “high” or “low” urgency based on previous research for both unimodal and bimodal combinations. Participants were capable of subjectively judging perceived urgency independent of response time and responded to bimodal (relative to unimodal) and high (relative to low) urgency stimuli with significantly greater brake force. However, both factors interacted with cognitive demand indicating that the magnitude of these differential responses was reduced under high demand. Implications for warning evaluation in an in-vehicle driving context are discussed.