baby reproduction
Babies respond more to faces than any other stimuli. Istock

Babies respond more to faces than to any other stimuli, and now scientists have shown that this is also the case for foetuses in the third trimester of pregnancy. Human preferences for faces thus appear to develop in the womb.

The study, published in the journal Cell, is the first to successfully explore visual perception in babies before they are born.

Scientists have known since the 1960s that babies look at face-like shapes more than any other shapes but it wasn't until the 1990's that the mechanism behind this preference became clearer.

Researchers indeed showed that babies preferred to look at images where most of the information was contained in the upper part of the picture – such as faces which have the two eyes and nose in the top part.

In the present research, the scientists projected light through the uterine wall of pregnant mothers to present foetuses at 34 weeks gestation with patterns of light. These were shapes made up of spots of light, and some appeared 'face-like' - with two spots of light at the top and one at the bottom (see image below).

"At birth the visual acuity of babies is quite bad, for them faces appear as quite blurry and similar in many ways to the face-like shapes we exposed them to in the study," lead author Vincent Reid of Lancaster University in the United Kingdom, told IBTimes UK.

With his team, he tested the responses of 39 fetuses to face-like patterns of light presented to them in both upright (face-like) and inverted orientations.

A conceptual illustration of the stimuli used in the current study. A and B represent face-like shapes, with most of the information at the top of the image.

The scientists discovered that the fetuses were more likely to their heads to look at face-like images over other shapes - a sign that they were more engaged with them.

"There was the possibility that the foetus would find any shape interesting due to the novelty of the stimulus," 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."

Clinical applications

Technical issues have long prevented this kind of research. One of the most important aspects of this study is that it describes an innovative technique to investigate foetal vision and cognition in the womb, which involves shining light through mother's tissue into the uterus.

Here, the scientists showed that much more light than previously thought can penetrate through maternal tissue and can be seen by the fetus. Thus, it is possible to expose fetuses to visual light stimuli and to study their reactions. The development of high quality 4D ultrasound has broken down the last technical barriers, allowing observations of these reactions in unprecedented details.

The study can help scientists improve their knowledge of foetal development and about when and how visual perceptions and preferences for faces arise.

"We show that foetuses actively respond to their environment. They are not passive in what they are learning about the world. In our study they actively engaged with the stimuli and moved their heads to track the face objects. As such, this study helps us move forward with our understanding of foetal development", Reid said.

"Different theories have been developed to explain our preference for faces, one of which is that it is linked to the experience at birth, with faces being one of the first things that babies see. But other options are that this preference is innate and encoded in our genes or that it arises in response to something in the prenatal environment. Considering our findings this last hypothesis is likely," he added.

He also says that the findings could have clinical applications in the future. For example, when today some foetuses go through heart surgery in the womb, there is always a concern that they were inadvertently deprived of oxygen during the intervention.

To check whether this is the case, doctors typically check whether infants after birth have normal visual responses - with this new technique, this could be done much earlier, before they are even born.