The real reason cars and cellphones do not mix

TALKING on a cellphone is more distracting for a driver than talking to a fellow passenger. And now we may know why.

While a car is moving, the strength of signal received by a driver's phone continually changes, and the phone often has to switch from one base station to another during a call. That causes a slight loss of sound quality, forcing the driver's brain to work harder to work out what the person at the other end is saying, say Takashi Hamada and colleagues at the National Institute of Advanced Industrial Science and Technology in Tokyo, Japan.

Hamada's team measured the sound quality of mobile phone calls in parked cars and in cars travelling at 65 kilometres per hour. A comparison of the two types of voice signal revealed silent periods of about 300 milliseconds interrupting the signal roughly six times a minute. They also discovered a time lag of about 300 milliseconds for a phone in a moving car, while for 5 per cent of the time, the frequency range becomes distorted.

The researchers then played 11 volunteers an audio recording of a story that included similar interruptions. As the volunteers struggled to hear the distorted parts of the recording, their right parietal cortex, the part of the brain that perceives sound, became more active (Transport Research Part F, DOI: 10.1016/j.trf.2005.04.016).

Previously, it was assumed that speaking to passengers was less distracting because they stop talking when the driver needs to concentrate.

[ needs more salt ]