Parents have been warned of the negative effects of too much screen time for their babies. A new study found that infants exposed to computer, TV and phone screens for hours could suffer lower cognitive skills later in life.

In a study titled “Associations Between Infant Screen Use, Electroencephalography, Markers and Cognitive Outcomes,” published Monday in JAMA Pediatrics, researchers examined the association between infant screen use and cognitive impairments with the help of electroencephalography markers.

The birth cohort study involving 437 children found evidence that electrocortical activity in the frontocentral and parietal brain regions was affected by long-term screen exposure. This led to executive function impairments later on.

Toddlers who spent time watching device screens for an average of two hours per day were found to perform worse or have poor executive functions later on, at age 9.

The study’s researchers defined executive functions as “a collection of higher-order cognitive skills essential for self-regulation, learning, and academic achievement, as well as mental health.”

To measure how screen time affected the cognitive skills of the children, the research team asked their parents to report the average amount of screen time consumed by the babies at age 12 months on weekdays and weekends each week.

They then proceeded to collect power spectral density from electroencephalography at age 18 months. A follow-up was performed when the kids were aged 9. Their attention and executive functions were measured using teacher-reported questionnaires and objective laboratory-based tasks.

The study did not provide evidence that excessive screen exposure directly leads to lower cognitive functioning. Other factors were also found to affect the cognitive functioning scores of children, as pointed out by ABC News.

The team acknowledged that further efforts are needed to distinguish the direct association of infant screen exposure with executive function impairments.

The American Academy of Pediatrics recommends no screen time for children until 18 to 24 months, except for video chatting. Kids between 2 and 5 are recommended to only have an hour or less of screen time per day. The World Health Organization also recommends no screen time for kids below the age of 2, according to the American Psychological Association.

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A boy plays a soccer game on his Ipad inside a mass rapid transit train in Singapore on June 8, 2012. Roslan Rahman/AFP/Getty Images