Early signs of visual awareness emerge in human babies five months after being born, a study has shown.

A weak spark of conscious perception can be measured in five-month-old infants which strengthens with age.

The discovery may provide a new method of assessing patients in vegetative or minimally conscious states.

Demonstrating visual consciousness in infants is difficult because, like some patients with severe brain injuries, they cannot report what they have seen. Eye movements may indicate awareness but can be misleading. In adults, eye movements have been observed even when brain activity linked to conscious perception is absent.

The new research focused on an electrical signal produced in the brain when someone notices and is aware of a visual scene observed very briefly.

The same signal was seen in babies shown a series of faces for a fraction of a second.

The signal appeared in all infants aged five to 15 months, but was “weak and delayed” in the youngest.