Do NOT Drink and Drive: Why?

Everyone has heard the saying “don’t drink and drive” and have accepted this seemingly as a law of nature: YOU DON’T DRINK AND DRIVE unless you want the vehicle you’re driving to end up in a curb somewhere.
This puts up a question: other than feeling groggy, how exactly does drinking alcohol affect one’s driving?  What is it with a drunken person’s perception that puts them into trouble?

"Is my parking good enough?"

As Nawrot has put it, many studies have already established the effect of alcohol and fast and slow eye movement. Fast eye movement concerns saccadic eye movement, foveating (thus focusing) an object of interest. Slow eye movement on the other hand is concerned with the maintenance of fixation on an object when the perceiver and/or the object of interest is in motion. Both these systems’ performances are affected by alcohol intoxication, reducing their effectiveness. Specifically, fast eye movement initiation and velocity is slowed. On the other hand, slow eye movement gain (eye velocity / target velocity) becomes too slow to be effective. The latter would induce fast eye movement in order to compensate with the inability of slow eye movement to track an object of interest. This movement is called “gaze nystagmus” and is an important component in field sobriety tests.

"I am not the police officer you are looking for"

Nawrot’s study focused on the effect of the influence of alcohol on motion parallax which is affected by the lowered gain of slow eye movement. Slow eye movement is an essential component in motion parallax where fixation on the object of interest should be maintained in order to infer an accurate depth perception, the discrepancies in the apparent velocity of the object being a cue for depth. Using a repeated measures design, he tasked his participants to simply follow a dot moving in a sinusoidal pattern while moving, either actively (active motion parallax) or passively (passive motion parallax). He contrasted the results of those that were influenced by 100 proof vodka and orange juice from those who weren’t. The results of the study suggested that the alcohol-deterred slow eye movement significantly affected depth perception. This induced a weaker tracking ability and elicited gaze nystagmus which indicates that you wouldn’t be focusing on the object well when drunk! This either means that drunk people fail to see how far objects are because they aren’t able to track it’s apparent movement, or they just didn’t see it because they’re just too drunk (as to alcohol’s influence on fast eye movement).



Nawrot, M. Depth perception in driving: Alcohol intoxication, eye movement changes and the disruption of motion parallax. Department of Psychology, North Dakota State University, Dakota, USA.


~ by myfivesenseworth on September 20, 2011.

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