A study of children exposed to recreational drugs in the womb has turned up the surprising result that marijuana can improve how they see moving things.
Children exposed to marijuana were 50 percent better at the global motion task - detecting movement of signal dots against the background "noise" of other dots - than children who weren't exposed, University of Auckland scientists say.
Their study, which looked at 145 four-and-a-half year olds who were exposed to different combinations of methamphetamine, alcohol, nicotine and marijuana before birth, was published in Nature: Scientific Reports this week.
Most studies have investigated how recreational drugs impair motor and cognitive development in children, but the impact on visual areas of the brain is less well understood, says doctoral researcher Arijit Chakraborty.
The 50 percent improvement in the global motion task for children exposed to marijuana in the womb was an unexpected result, he said.
It was found that when mothers drank alcohol alone their children's motion perception was impaired, but when they consumed both marijuana and alcohol there was no effect - "suggesting that the benefits from marijuana cancelled out the harm from alcohol".
"This perhaps has implications for preventing some of the effects of Foetal Alcohol Syndrome."
Prenatal exposure to methamphetamine had no influence on vision.
The majority of the study's children (81.3 percent) had been exposed to multiple drugs. Twenty-five children (15 percent) had no drug exposure and provided a non-drug exposed control group.
The mothers' prenatal drug exposure was verified by meconium analysis.
Other visual functions, such as measures of visual acuity were not affected by drug exposure.