Well, the sobriety tests themselves are divided attention tests. They don't mimic what you do driving, but they divide your attention between what your mental process is and the physical tests that are being done. As with driving, you're multi-tasking. These tests are simply to have you multi-task. If you can't multi-task, then you probably shouldn't be driving.
The indicators that we look for are different from test to test. We can't categorize drugs based on the sobriety test. All we can do is say the person is either impaired or not impaired, or believed to be impaired. In order to say whether it's drugs, alcohol, fatigue, a medical issue, we have to go through the entire evaluation. There are four drug categories that affect the eyes in one way, three that don't—how people react to light, their pulse rate is different for different categories, their blood pressure is different, body temperature, and the person's muscle tone.