None of the above, says Lexus. The most advanced computer in the modern car is you, the driver.
You're the computer Lexus knows least about, but also the one that can process more information than any other and with more ultimate safety outcome than any of the other in-car systems.
That's why Lexus has built a hugely expensive and, well, just huge driving simulator, to monitor the behavior of drivers behind the wheel. The simulator itself is 20 feet across, 15 feet tall, tilts up to 25 degrees to simulate cornering forces and can simulate speeds of up to 186 miles per hour. Six hydraulic rams provide movement and the whole capsule sits inside an enormous room, moving in any direction necessary to simulate the movement of the car inside.
A Lexus GS sits inside the capsule and is surrounded by 360 degrees of screens to immerse the drivers in whichever scenario the Lexus engineers choose. The car and interior are surrounded by cameras too, to monitor the driver's reactions. Lexus is testing drivers' reactions to situations and monitoring how they react when tired, to emergency situations, and how operating in-car features affects their driving.
By studying drivers Lexus hopes to understand how they can tailor in-car systems to best work with the occasionally flawed organisms that control them...