If you think one or two small drinks won't affect your driving skills, read on. New NASA-led research has warned that hand-eye coordination in driving and other activities is compromised after consuming the equivalent of less than a half of beer, for a person around 75 kg in weight.
The findings provide new information on the potential impact of even minimal alcohol consumption on high-risk human activities that rely on keen visual and visuomotor control, like driving, piloting, or working heavy machinery.
In previous studies, eye movements and vision were only affected at blood alcohol concentrations (BACs) approaching the legal limit for driving.
The study from the research team based at NASA's Ames Research Center in California found for the first time that hand-eye coordination is dramatically more sensitive to alcohol with some measures of coordination impaired by more than 20 per cent at BAC levels as low as 0.015 per cent.
"Our findings provide a cautionary tale that the subjective experience of drunkenness is often not aligned with objective impairment of sensorimotor coordination. In other words, most people feel they are unimpaired after one drink, yet they are to a significant degree," said Terence Tyson, first author on the study in a paper published in The Journal of Physiology.
Driving may be affected by drinking just a small amount of alcohol, even though the driver may feel fine and be well within the legal limit, Tyson added.
To reach this conclusion, the researchers measured volunteers' eye movements, pupil responses, and BAC, multiple times during a day while they performed a specially designed task, before and after they drank alcohol.
At random, the volunteers were assigned a mixed drink containing a certain quantity of alcohol achieving either the higher (0.06 per cent) or lower (0.02 per cent) peak BAC levels so that they were not aware of exactly how much they drank on a given day.
The researchers then computed 21 different ocular measures that have been shown to assess neural processing in specific brain areas that contribute to different components of the eye-movement and pupillary responses.
The study participants were men and women, mostly in their 20s, who drink on average 1-2 drinks per week.
The researchers made sure that participants had a full night's sleep the night before, and asked that they abstain from both alcohol and caffeine consumption for several nights in a row prior to testing.
Apart from this finding specific to alcohol-induced impairment, this study further demonstrated how an especially designed collection of non-invasive eye measurements can be used to measure mild deficits of processing in the brain.
In future studies, the researchers plan to look at how their eye measurements are affected by other types of neurological conditions, such as those caused by degenerative diseases or toxic exposures.
NASA is interested in developing sensitive yet non-invasive methods for detecting mild impairments.