The one that does not talk

Marie-Catherine Mousseau writes about the latest advances in our understanding of the perceptual abilities of young infants

Have you ever wondered what the world looks like for very young babies? According to the 19th-century philosopher and psychologist William James, the visual world of infants is a ‘booming, buzzing confusion’. No wonder. With a visual acuity six times less than that of adults, a difficulty focusing beyond 22cm and no experience of the outside world whatsoever, the newly born infant’s interpretation of its surroundings is likely to be random and chaotic.
Many early experts in the area shared James’ view. The empiricist John Locke and the constructivist Jean Piaget believed that the infant at birth is a blank slate – a tabula rasa – and has to construct all its knowledge of the world progressively through experience. There is a contrasting view, though.
This is the view held by the philosophers Kant and Descartes, and all the nativists, who held that at birth or very soon afterwards, the infant is capable of some kind of meaningful perception of the world.
According to the nativists, babies can make sense of unified objects surrounding them, thanks to some innate, in-built representation of their environment and its laws.
How do we go about determining who is right, the empiricist or the nativist? The word ‘infant’ comes from the Latin infantem, from in (‘not’) and fari (‘talk’): the one that does not talk. How have we learned about an infant’s perception of the world, about how they make sense of what they see, hear, and touch, when they cannot tell us? Psychologists had to find intelligent ways to address this question.
The sensory system
A first step has been to look at the maturity of their sensory system. Neurological and anatomical studies were pioneered in the 1960s on the neonatal primary cortex of cats and monkeys. While these showed that it takes six to eight months for the visual system to mature, in recent years, however, it has become increasingly clear that visual processing at birth is far more developed than previously thought. As to the auditory system, evidence suggests that even in newborns, it is very sophisticated.
But the level of maturity of their sensory systems does not indicate how the infants make sense of all this sensory input. Are they, as James suggested, swarming in a booming, buzzing confusion, or can they very early on make some sense of reality, as believed by the nativists?
Behavioural experiments
Cleverly designed behavioural experiments provided critical elements of answer. These were pioneered in the visual area by the work of Robert Fantz in the ‘50s in an approach called preferential looking. Its principle is simple: a baby looks longer at a visual stimulus that interests it more. And if the baby consistently looks longer at one stimulus over another, it means that it can tell the two stimuli apart.
For stimuli that are equally preferred, the researchers came up with a variation of this method, taking advantage of a process called habituation. They repeatedly show one stimulus until the baby gets bored and stops looking at it. If the second stimulus appears different to the baby, then it will show interest again (novelty effect). The overall technique has been extended to evaluate hearing preferences (e.g. by looking at the direction the baby turns its head).
Using this type of approach, psychologists have made a number of discoveries. In the auditory arena, infants have been shown to prefer their mother’s voice. They also prefer listening to what is called ‘motherese’ (high-pitch, infant-directed speech). In the visual arena, infants prefer looking at curved features, moving targets and 3D objects.
Interestingly, many of the discoveries that have been made support the nativist theory. Evidence has indicated that babies can see patterns very early, and contrasted colours as early as two weeks of age. Face processing, in particular, has been the focus of many studies.
We now know that babies just 12 hours old prefer looking at their mother’s face over the face of a stranger. And very early on, babies show a strong preference for looking at faces in general, and among faces, looking at average faces – a preference that appears at less than three days from birth.
This has led some researchers to conclude that babies have an innate representation of a ‘prototype’ face. This would mean that face recognition is innate and hardwired, supporting the nativist theory. An inbuilt ‘prototype face’ would also explain the capacity babies have to imitate facial expressions of adults — and this, only minutes after birth.
But behavioural experiments have also showed that not all mechanisms underlying our visual representation of the world are innate, far from it. It takes babies two months to get a unified view of objects with hidden parts, and five-six months to realise that two touching objects are not just one; at six-eight months, they learn about gravity and support, and between six-nine months, they learn about depth perception. Thus, the empiricist theory still holds plenty of water. Babies undoubtedly need to experience the laws of physics to make complete sense of what is happening around them and to them, and to react appropriately.
Interestingly, alongside perceptions that are innate, and others that get more sophisticated with experience, there are perceiving abilities that are decreasing. In the auditory arena, the ability to discriminate phonemes has been shown to be higher in young infants (who can discriminate phonemes outside their native language) than in adults (who only distinguish phonemes used in their own language).
The same rule seems to apply in the visual arena. Pascalis (2002), using a habituation paradigm, was able to show that six-month-old babies can discriminate between two monkey faces as well as between two human faces, while nine-month-old babies and adults can only discriminate between human faces. So, surprisingly, there are things that babies can do better than us!
Remaining questions
Many of these findings, whichever theory they support, appear to be coherent in an evolutionary perspective. An evolutionary advantage for babies to very early recognise their mother’s face and voice would be to strengthen the bond with their carers, on whom their survival depends completely, and attract their attention.
More generally, faces are the markers of social interaction on which the baby relies for learning. The disorder called prosopagnosia, whereby a lesion in a specific area makes sufferers unable to recognise faces, supports the idea of specialised brain processing, specifically dedicated to human faces.
The superiority of young infants in discriminating phonemes and other species’ faces compared to adults also makes sense. Babies possess much more neuronal connections than adults. They start with broader neuronal processing possibilities before selecting the ones that are adapted to their environment and needs, thus saving brain resources and energy.
However, there is still a lot of room for discussion and questioning. The study showing an innate preference for average faces, leading some psychologists to hypothesise a ‘prototype face’ innately present in the brain, is difficult to explain in neurological terms.
It is also possible that the results were just illustrating the early preference for faces similar to the carer’s face – the carers involved in the study are likely to be young females with average faces!
Romulus and Remus
One may also wonder how the preference for faces would be like in babies raised by monkeys. After all, according to Pascalis’ experiments, younger infants are better able to discriminate monkey faces than older infants or adults, even though these are quite far from the average human face. And what would have happened to Romulus and Remus, the two infants raised by wolves; would they not have grown up showing a preference for wolf faces?
It might be argued that, from babies’ ability to discriminate and learn quickly about patterns, there follows their ability to learn about faces and quickly recognise the faces of their carers… no matter how odd these might be.
The capacity of newborn babies to imitate adult facial expressions does not necessarily prove the existence of an inbuilt representation of their own face, either.
It is now known that the brain possesses mirror neurons that get activated in exactly the same way in the brain of someone performing an action or someone just looking at the action being performed. These mirror neurons, if present at birth, might be associated with an infant’s ability to imitate.
Also, while babies’ early discrimination and preference for their mother’s voice makes sense, it is more difficult to explain the preference for a motherese voice.
Further research actually suggests that the results rather reflect the preference for a ‘happy talk’.
According to these newer findings, it is actually the positive emotion conveyed by the motherese voice that makes the baby turn its head. Would this also apply to negative emotions? Being able to quickly perceive emotions in general (happiness but also anger or fear) would have an obvious social and survival interest and it would make sense that this empathic ability is innate or appears very early.
Dynamic, multi-sensorial real world
Infants, and more so very young infants, are by their very nature unpredictable and unstable. Dynamic transformations and reorganisations are going on relentlessly in their bubbling brains that they cannot verbally express. The behavioural methods described above have proved to be consistent and reliable, and have given us a valuable insight on how babies perceive the world, which was not intuitive and even contradicted previous beliefs.
Both nativists and empiricists have valid points. The baby is not just the receptacle of buzzing disparate sensations. Their auditory system is very mature, and their visual system is much more mature than previously thought, with some innate organised representations of the world (e.g. possibly face processing), some predispositions to construct others quickly (e.g. physical laws) or on the contrary to cut down on abilities that are less critical (phoneme outside their native tongue or other species discrimination).
However, some results still require careful interpretation and support from further experiments.
Finally, the sensory picture of the real world is much more complex and dynamic than the isolated static stimuli tested in the lab. A baby’s brain develops and constructs neuronal networks where some synapses are strengthened and others pruned in response to a very rich environment overloaded with bustling sensory input.
No wonder that it is where it functions at its best. Controlled lab experiments are definitely necessary to identify general principles underlying the basis of infant perception.
However, ‘ecology valid’ experiments conducted in the real world are also critical if we are to get the full measure of what the world is like for babies. While deepening our knowledge of human development, this understanding might also help predict and prevent cognitive disorders which can develop later in life.
References on request.
l Marie-Catherine Mousseau holds a PhD in Neurosciences and is
Editor of MIMS Ireland.
l The views expressed above are those solely of the author(s) and in no way may be deemed to reflect the views or policy of either MSD Science Centre or MSD.