A new study using electroencephalographic (EEG) recordings of brain responses of five-month-old infants showed that they can individuate faces of their mothers i.e., generate specific neural responses associated with recognition of faces, when briefly shown pictures of their mother’s face, but only under certain conditions.
The findings indicate that young infants can identify their mother’s face at a glance, under different angles and with different facial expressions, but only if it is not mixed with too many other faces. The study was published in the Cortex.
Recognizing people based on their faces is extremely important for social interactions. This is also a very complex task. Yet, in spite of its complexity, adult humans are typically able to recognize the identity of thousands of faces. They can also do it extremely quickly, at a glance, in less than a second.
Previous studies have shown that it is much easier for people to recognize familiar faces under different view angles and with different facial expressions than to select matching pictures showing unfamiliar faces. This is called “the familiarity effect” of face identity recognition. The familiarity effect has been studied extensively in previous years, but age at which it develops and neuropsychological mechanisms it uses are still an unknown.
“We as human adults are experts at face recognition,” explained study author Stefanie Peykarjou of Heidelberg University. “We easily recognize large numbers of familiar faces and even unfamiliar ones in the blink of an eye. I am intrigued by the question how this ability develops! Every mother knows that her baby recognizes her in real life – based on her smell, voice, and looks. But can they do it based just on an image? What if they see their mom in a photo album, will they recognize her?”
To explore whether the familiarity effect of face identity recognition exists in infants, Peykarjou and her colleagues recorded brain responses to exposure to faces of 39 five-month-old infants using electroencephalography (EEG). Authors chose infants of this age because previous studies have shown that five-month-olds can already recognize faces. However, those studies showed faces to infants for longer times, so it remained unknown whether infants of this age can recognize faces at a glance and in different conditions, the way adults do.
The authors applied the fast periodic visual stimulation (FVPS) stimulus exposure design in which pictures of faces are presented to participants quickly but repeatedly. One of the faces in the group is called a target and that is the face the study participant is expected to recognize. In this case, it was either infant’s mother or the face of a stranger the infant had a chance to familiarize with.
The whole procedure would start by exposing the target face to the infant for 30 seconds, so that the infant could familiarize him/herself with it. After that, a procession of images of faces, each shown to the child for a very brief moment, would continue. Each infant underwent up to 12 such trials.
Infants were divided into two groups. The first group (17 infants) was shown a series of pictures in which the target face was present often i.e., 80% of the pictures contained the target face and the number of different faces shown was low. Infants in the other group (22 infants) were shown a series of pictures in which the target face was rare (20%) and there were much more different faces on the pictures. Faces on the pictures had different facial expressions and head orientations.
The researchers expected that brains of infants participating in the study would show an activation scheme called individuation that is linked to face recognition and that the degree of familiarity with the face will influence the magnitude of the individuation response. They also established a set of other hypotheses about expected individuation reactions in different face exposure conditions.
Analysis of the EEG recordings showed clear individuation responses when mother’s face is presented and in the group where it was presented often. In other exposure situations, brain individuation responses were much lower or nonexistent. The results showed that infants are able to identify their mother’s face even when they see it at a glance and with different angles and facial expressions, similarly to how older humans do.
“Even within 170 ms (that is 1/6 second, or one eyeblink), 5-month-olds can recognize their mother!” Peykarjou told PsyPost. “Their brain shows a strong response to her face if it is embedded in a stream of unfamiliar women. But even more: They can even differentiate an unfamiliar female from others, just based on briefly presented pictures. (The response was weaker than for moms, though.) This means to me that the infant brain is prepared to recognize people, most likely to facilitate attachment and social relationships.”
Infants, however, require mother’s face to be presented often. When mother’s face was presented as a rare picture, among faces of many different strangers, no individuation response was obtained.
The researchers say that this is the first study “reporting a proficient human face identity recognition in the first year of life across head orientations and facial expressions at a high speed of presentation.” It should be noted though, that the study employed pictures of faces that included outer facial features, such as hair, and the results might differ if the infants were presented faces without the outer features.
“We are currently finishing the next study where I or my colleague play with the participant before the EEG test phase, and we appear as target faces in the presentation,” Peykarjou said. “I am really curious to see if this kind of interaction familiarization is sufficient to boost recognition, so that infants recognize our faces better than the ones just familiarized with a picture. (This is like meeting a friend with her baby – will the baby recognize you after 10 minutes of interaction?)”
The study, “Superior neural individuation of mother’s than stranger’s faces by five months of age”, was authored by Stefanie Peykarjou, Miriam Langeloh, Elisa Baccolo, Bruno Rossion, and Sabina Pauen.
