A new study, led by researchers at Lancaster University in the United Kingdom, reveals that babies show a preference for faces while still in the womb. This discovery opens up a new area of prenatal research, say researchers.
Prof. Vincent Reid, lead researcher of the study and psychologist at Lancaster University, worked with collaborators from Blackpool NHS Trust, the University of Cumbria, and Durham University, all in the U.K. Their findings were published in Current Biology.
Previous studies have indicated that infants at birth prefer to engage with faces rather than other forms of stimuli. Until now, however, it was unknown whether or not this preference was present in babies before birth.
The new study analyzed fetal head turns in response to visual stimuli projected through the uterine wall. In total, 39 fetuses at 34 weeks gestation were presented with upright and inverted face-like imagery. Their responses were monitored with high-quality 4-D ultrasound.
Upright and inverted "faces" - consisting of three dots in the shape of a triangle - were projected onto the mother's abdomen. Both image types were shown to one side of the baby's face and moved horizontally away from the baby to see whether their head would turn.
While the fetuses moved their heads to track the upright face-like patterns, no such movement was observed with the inverted projections. These results demonstrate that it was not the pattern itself that the fetus liked best, but the particular arrangement of dots likened to a face shape.
"There was the possibility that the fetus would find any shape interesting due to the novelty of the stimulus," explains Prof. Reid. "If this were the case, we would get 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."
These results show that after birth, babies do not necessarily need to experience several faces to indicate a preference for gazing at people. This preference already exists before they are born.
"This rules out the idea of filial imprinting, in the way that ducklings imprint on their mother, because we have shown that the preference for face-like shapes is already present before birth," Prof. Reid continues.
4-D advances open up 'whole new field' of fetal observation
Analysis of the human eye has previously shown that there is significant biological development of the eye from around 25 weeks gestation. Preterm birth studies have also shown that babies can visually fix and track from 32 weeks gestational age.
In the present study, Prof. Reid and colleagues have illustrated that fetal visual perception can be analyzed during the third trimester, mostly due to the technical advances in 4-D ultrasound that grant access to viewing accurate fetal behavior.
The researchers note that in the future, other aspects of infant perception could be examined in the third trimester, such as biological motion processing.
"I would also say that if you are pregnant, don't go shining bright lights into the face of your fetus. We were very careful and made sure that the light was bright enough to enter the womb but not too bright as to be unpleasant or aversive for the fetus," cautions Prof. Reid.
"We are improving the light source and plan to examine other aspects of fetal perception and cognition via visual systems. All sorts of aspects of human vision can now be explored."
Prof. Vincent Reid
"Newborns can discriminate numbers and quantities. Does the fetus in the third trimester also have these capacities? Exploring the transition from fetus to infant is also a very exciting possibility," Prof. Reid concludes.