Presentation Level and the Attentional Workload of Comprehending Verbal Messages: Implications for Design of Verbal Warnings

Verbal warnings are designed to alert as well as provide information to an operator who is likely to be performing several simultaneous tasks. Yet, research generally ignores the potential of presentation intensity to alter the attentional demands placed on the operator by verbal warnings in multi-task environments. Results of the current investigation demonstrate that as the presentation intensity of speech stimuli decreased from 70 to 50 dB, participants made more auditory processing errors, but only when required to perform a simultaneous simulated driving task. Auditory task performance did not differ significantly between conditions in single task trials. However, as signal presentation level decreased, participants made significantly more incorrect responses in both an auditory mental arithmetic task and a sentence processing task while driving performance remained unchanged. Results are discussed in terms of their implications for the design of verbal displays and warnings for use in transportation settings particularly with older, hearing impaired listeners.