It is extremely dangerous to talk over one's mobile phone while driving a vehicle. The cost of switching activities may be in terms of accuracy and response time, as efficiently switching over to a new task can be prevented by structural cognitive limitations, according to Oregon State University's Assistant Professor of Psychology Mei-Ching Lien.
This includes simple tasks also. The studies that Mei-Ching Lien conducted in association with her NASA Ames Research Center colleagues reveal that humans have a fundamental inability when it comes to switching over from one task to another. The Journal of Experimental Psychology has published the results of the study.
The responses of several volunteers were studied while responding to visual and auditory cues. The responses were invariably delayed when a second element was introduced. Practice can perhaps reduce the delay, but it cannot be eliminated altogether. Talking over cell phones while driving is particularly dangerous as it results in slow reaction and even inattention. It cannot be compared to, listening to a radio program wherein a person is not obliged to respond to questions.
It may take about 300 milliseconds while responding to a single stimulus, which will rise to 800 milliseconds when an additional task is added. None of the volunteers were immune to the delays in multi-tasking. The ones who play video games frequently were decidedly at an advantage. The result of the study is that greater efficiency can be attained by simplifying one's tasks.