Watch where you step... We have trouble while dual tasking with visual, attentional deficits. In other words, you don't see stuff. That's probably one of the reasons they are trying to ban texting while crossing the street in Honolulu.
"The results revealed that the size of visual field and visual acuity demand were varied across the visual task conditions. Approximately half of the visual cues provided during texting while walking were not perceived as compared to the visual task only condition. The field of regard loss also increased with increased dual-task cost of mobile phone use. Dynamic walking stability, however, showed no significant differences between the conditions. Taken together, the results demonstrate that the loss of situational awareness is unavoidable and occurs simultaneously with decrements in concurrent task performance. The study indicates the importance of considering the nature of attentional resources for the studies in dual-task paradigm and may provide practical information to improve the safe use of mobile phones while walking."
Lim J, Chang SH, Lee J, Kim K. Effects of smartphone texting on the visual perception and dynamic walking stability. Exerc Rehabil. 2017 Feb 28;13(1):48-54. doi: 10.12965/jer.1732920.460. eCollection 2017 Feb. link to full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5331999/