On timing and modality choice with local danger warnings for drivers

We present an experimental study on the effectiveness of five modality variants (speech, text-only, icon-only, two combinations of text and icons) for presenting local danger warnings for drivers. Hereby, we focus on sudden appearing road obstacles within a maximum up-to-date scenario as it is envisaged in Car2Car communication research. The effectiveness is measured by the minimum time necessary for fully interpreting the content. Results show that text-only requires the most time while icon only is perceived the fastest. The two combined versions lie in between. The minimum length for speech is determined by the duration of the utterance, which is longer than perception time of text-only in this case. However, speech could be decoded reliably by nearly all subjects. Results indicate further that a blinking visual cue provided through the periphery visual channel is able to enhance the saliency of visual modalities. Subjective judgements by the subjects furthermore suggest a combined use of visual and auditory modalities