Fetuses in the late stages of pregnancy move their heads towards shapes that resemble faces, suggesting that the ability to recognise faces may be innate.
While hearing, touch, taste and balance have previously been looked at in fetuses, vision has not been studied because of technological challenges. But the availability of 4D ultrasound has changed this, giving researchers the ability to track fetuses' movements in the womb.
'In our study they [the fetuses] had to move their head to keep looking at the face-like stimulus when we moved it away from them,' said lead researcher Professor Vincent Reid at Lancaster University. 'So they are active participants in finding information from the environment.'
Babies prefer to look at faces over other visual stimuli, so the team wanted to see if face-like stimuli elicited responses in fetuses.
In the study, published in Current Biology, researchers created two patterns using dots of red light. They formed a triangle to create a non-face stimulus and an inverted triangle to mimic eyes and a mouth. These light patterns were shone through the uterine wall of 39 women at 34 weeks of pregnancy.
Fetuses preferentially turned their heads in response to the face-like pattern of lights, while the non-face pattern of lights elicited no response.
'There was the possibility that the fetus would find any shape interesting due to the novelty of the stimulus,' Professor Reid said. 'If this was the case, we would have seen no difference in how they responded to the upright and upside-down versions of the stimuli. But it turned out that they responded in a way that was very similar to infants.'
The research indicates that the preference for facial stimuli may begin in the womb. It also suggests that fetuses have enough light to be able to see, according to the researchers.
'This study suggest the fetus's visual world might, in fact, be more interesting and contain more structure and visibility than we'd previously thought,' said Professor Mark Johnson, at Birkbeck College, London, who was not involved in the work. He told NPR: 'This new technique allows us to get a window into their visual world.'
'[This research] would be quite important because it would tell us that the ability of the brain to integrate information across senses is present very early on, even prior to birth,' Professor Johnson added.
Nonetheless, Professor Reid warned that pregnant mothers should avoid shining bright lights through their abdomen in case they damage their unborn child's eyes.