Passengers in self-driving cars will likely experience more episodes of motion sickness or car sickness since they'll do things that worsen this common problem.

Some six percent to 12 percent of American passengers in autonomous vehicles will probably suffer from moderate to severe motion sickness since they'll have more time for activities that aggravate motion sickness like texting or reading, said research from the University of Michigan Transportation Research Institute.

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The most common results of motion sickness or kinetosis are severe headaches, nausea and vomiting. Motion sickness is also called airsickness or seasickness.

"Motion sickness is expected to be more of an issue in self-driving vehicles than in conventional vehicles," said Michael Sivak, who along with Brandon Schoettle of U-M conducted the research.

"The reason is that the three main factors contributing to motion sickness -- conflict between vestibular (balance) and visual inputs, inability to anticipate the direction of motion and lack of control over the direction of motion -- are elevated in self-driving vehicles.

"However, the frequency and severity of motion sickness is influenced by the activity that one would be involved in instead of driving."

The U-M report found that over 60 percent of Americans will pass the time in a self-driving car by watching the road, talking on the phone or sleeping, which are activities that don't normally lead to motion sickness.

It's the remaining 40 percent that will read, text, watch movies or television, play games or work that will be more prone to car sickness, said the research.

In their research, Sivak and Schoettle asked some 3,200 adults in the U.S., India, China, Japan, Great Britain and Australia what kinds of activities they would do instead of driving in a fully self-driving vehicle. Many of these activities could cause motion sickness.

More than a third of Americans said they'd do things that increase the chances and severity of motion sickness. More than half of Indians, 40 percent of Chinese and 26 to 30 percent of adults in Japan, Great Britain and Australia say they would engage in these kinds of activities.

From six percent to 12 percent of American adults riding in fully self-driving vehicles can be expected to experience moderate or severe motion sickness. The percentages are about the same for residents in India, China, Japan, Great Britain and Australia.

Sivak and Schoettle suggest manufacturers can design self-driving vehicles to lessen the likelihood of motion sickness. These design changes can involve maximizing the visual field with large, transparent windows; mounting transparent video and work displays that require passengers to face forward; eliminating swivel seats; restricting head motion and installing fully reclining seats.

Car sickness results from the sensory conflict arising in the brain from differing sensory inputs. The eyes mostly see the interior of the car which is motionless while the vestibular system of the inner ear senses motion. The effect is worse when looking down but may be lessened by looking straight ahead outside of the vehicle.