In this Papers Podcast, Charlotte Viktorsson, a PhD student at the Development and Neurodiversity Lab, Department of Psychology, Uppsala University, Sweden, discusses her JCPP paper ‘Preferential looking to eyes versus mouth in early infancy: heritability and link to concurrent and later development’ (doi.org/10.1111/jcpp.13724).
Charlotte is the first author of the paper.
There is an overview of the paper, methodology, key findings, and implications for practice.
Discussion points include;
- Why it is important to establish the relative role of genetic and environmental influences on eye preference relative to mouth preference in early infancy.
- What are the implications of what infants look at being largely based on their individual genotype, before they can select their environment by means of crawling or walking.
- Preference for eyes at 5 months was positively correlated with parent’s assessment of vocabulary at 14 months.
- No significant association was found between mouth or eye preference and later socio-communication difficulties, nor later autistic traits.
- How might these findings inform future practice or influence the way we think about infant development.
- How does an infant paying more attention to the eyes, compared to those that pay more attention to the mouth, appear to translate into later communication skills and learning?
In this series, we speak to authors of papers published in one of ACAMH’s three journals. These are The Journal of Child Psychology and Psychiatry (JCPP); The Child and Adolescent Mental Health (CAMH) journal; and JCPP Advances.
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Charlotte is a licensed psychologist from Finland who moved to Sweden in early 2020 to join the Development and Neurodiversity Lab and pursuing a PhD at Uppsala University. Her main research interests are early socio-communicative development and the etiology of early cognitive and social abilities. She has studied the heritability of several early behaviors in infancy, using eye tracking as the main measurement. She is interested in both typical and atypical development, with a specific focus on socio-communicative difficulties and autism.
- Video abstract ‘Preferential looking to eyes versus mouth in early infancy’ with Charlotte Viktorsson
- Feature paper ‘Preferential looking to eyes versus mouth in early infancy: heritability and link to concurrent and later development’, (2022). Charlotte Viktorsson, Ana Maria Portugal, Danyang Li, Maja Rudling, Monica Siqueiros Sanchez, Kristiina Tammimies, Mark J. Taylor, Angelica Ronald, Terje Falck-Ytter
[00:00:01.430] Jo Carlowe: Hello, welcome to the Papers Podcast series for the Association for Child and Adolescent Mental Health, or ACAMH for short. I’m Jo Carlowe, a Freelance Journalist with a specialism in psychology. In this series we speak to authors of papers published in one of ACAMH’s three journals. These are the Journal of Child Psychology and Psychiatry, commonly known as JCPP, the Child and Adolescent Mental Health, known as CAMH, and JCPP Advances.
Today I’m interviewing Charlotte Viktorsson, a PhD student at the Development and Neurodiversity Lab, the Department of Psychology, Uppsala University, Uppsala, Sweden. Charlotte is the first author of the paper, “Preferential Looking to Eyes Versus Mouth in Early Infancy: Heritability and Linked to Concurrent and Later Development,” recently published in the Journal of Child Psychology and Psychiatry. This paper will be the focus of today’s conversation.
If you’re a fan of our Papers Podcast series, please subscribe on your preferred streaming platform, let us know how we did, with a rating or review and do share with friends and colleagues. Charlotte, thanks for joining me, welcome. Can you start with an introduction about who you are and what you do?
[00:01:22.070] Charlotte Viktorsson: Yeah, thank you for having me, first of all.
[00:01:24.300] Jo Carlowe: You’re welcome.
[00:01:25.300] Charlotte Viktorsson: My name is Charlotte Viktorsson and I’m a licensed Psychologist from Finland and I’m currently doing my PhD candidate at Uppsala University in Sweden, and I study mainly early social development in infants using eye tracking.
[00:01:38.750] Jo Carlowe: Okay, well, let’s turn to the paper, “Preferential Looking to Eyes Versus Mouth in Early Infancy: Heritability and Link to Concurrent and Later Development,” recently published in the JCPP. Charlotte, can you give us a brief overview of the paper to set the scene?
[00:01:54.100] Charlotte Viktorsson: Yeah, of course. In this study we used eye tracking to explore where five-month-old infants look when they see videos of a woman either singing, talking or smiling, and specifically when we showed a relative, looking time at eyes and mouth, because these are the main areas that infants look at when they see a face. And the infants in this study were twins, meaning that we could also calculate the influence of genes and environment on the tendency to look at either the eyes or the mouth.
[00:02:19.920] Jo Carlowe: The primary aim of the study was to establish the relative role of genetic and environmental influences on eye preference relative to mouth preference in early infancy. Can you explain why this knowledge is important?
[00:02:32.070] Charlotte Viktorsson: I think it is important because we tend to measure a lot of different behaviours and abilities in children, trying to predict later outcomes. However, we still don’t know very much about why infants differ in these early behaviours and abilities. And we’re doing a twin analysis, like we did here. We actually get information about the aetiology behind these differences, and by doing that, we might understand what we can do to influence these behaviours, which might be valuable information when it comes to interventions, for example. So, I think this knowledge is important to further build on what we know about early infancy and how infants, through these early differences, diverge into individual pathways throughout development.
[00:03:14.340] Jo Carlowe: Great. What can you tell us about the methodology that you used for the study?
[00:03:19.319] Charlotte Viktorsson: The sample is part of the Babytwins Study Sweden, or BATSS, which includes 622 infant twins from the Stockholm area in Sweden, and the twin analysis utilises monozygotic or identical twins and dizygotic, or non-identical twins. And the monozygotic twins share 100% of their segregating DNA and dizygotic twins share, on average, 50% of their segregating DNA. And basically, we want to know whether twin one and twin two, in the monozygotic pairs, are more similar to each other than twin one and twin two in the dizygotic pairs are, and if they are, that suggests that their behaviour is influenced by genetic factors.
And to do a formal twin analysis, we used the OpenMx package, in R where we can do a more advanced calculation, giving us their relative influence of both genetic and environmental factors. And for the looking behaviour, we used a set of standard eye trackers, which, basically, is official formal camera that captures the gaze angle of the infants.
[00:04:18.290] Jo Carlowe: Great, and what were the key findings?
[00:04:21.020] Charlotte Viktorsson: First of all, we found that most infants had a tendency to look at the eyes, but there were some variation, where some infants tended to look more at the mouth almost all the time. This tendency to look at either the eyes or the mouth was stable across different conditions, so regardless of whether the woman was singing, talking, or just standing still and smiling, and this suggests that it is not related to low-level visual cue sort of stimuli, such as a moving mouth. And secondly, we found that the tendency to look at the eyes versus the mouth was quite highly heritable. Genetic differences between individuals explained around 50-60% of the variation in this measure.
[00:04:58.389] Jo Carlowe: I want to focus on that finding, that before infants can select their environment by means of crawling or walking, what they look at is largely based on their individual genotype. Can you elaborate on this? What are its implications?
[00:05:13.720] Charlotte Viktorsson: Yeah, I think this is the most fascinating aspect of this study, actually, because at this age, infants cannot move around on their own, but they can choose what to look at in their environment. So, they might focus on a parent’s face or a bright lamp, or a toy hanging above them, for example, and what you focus on will influence what you process. So, this, in turn, might shape your learning and development and might explain the different developmental trajectories that makes us all unique. And here, we show that differences in early visual preferences are, to a large part, due to genetics, which we did not know before. So, your genotype influence what you look at, at five-months-of-age, which is pretty interesting.
[00:05:56.370] Jo Carlowe: Yeah, surprising, actually. And in your paper, you note that a preference for eyes at five months was positively correlated with parents’ assessment of vocabulary at 14 months. What do make of this, because previous research shows an association between large vocabulary and a preference for looking at the mouth, rather than the eyes? So, that seems surprising.
[00:06:18.949] Charlotte Viktorsson: But this finding, it wasn’t actually very surprising, because earlier studies have found that the infants, at this age, mainly look at the eyes of other people.
So, earlier studies showing the association with their mouth looked at infants in the second part of the first year, but here, we look at five-month-old infants. So, here we did find that most infants had a tendency to look at the eyes and this might be related to their emerging ability of joint attention, for example. So, at around this age infants learn to follow other people’s gaze, which is known to facilitate word learning, and by following gaze, infants will attend to the same thing as their caregivers and, therefore, more quickly understand what they refer to when they talk about objects and events. So, our findings indicate that at this early age, attending to cues relevant for joint attention might be more important for later language than attending to speech cues linked to the mouth.
[00:07:14.900] Jo Carlowe: In your study in relation to mouth or eye preference, you found no significant association with later sociocommunication difficulties, nor later autistic traits. Can you say a little more about this?
[00:07:28.470] Charlotte Viktorsson: Yes, this is interesting, since the stimuli used in this study is videos of a person, so it’s, therefore, a quite social stimuli. However, this is a sample of typically developing infants, not infants with an elevated likelihood of autism or social difficulties. So, it is possible that an association would be find in such a sample, but that is only speculative and needs to be investigated further, of course. It is also possible that this measure simply is not important for later sociocommunicative abilities and maybe it doesn’t matter whether you look at the eyes or the mouth. Maybe the important thing is that you look at faces in general.
[00:08:03.610] Jo Carlowe: What else would you like to highlight from your paper?
[00:08:06.410] Charlotte Viktorsson: I think you’ve covered all of the important and interesting parts, but I do like to highlight the amazing amount of work put into collecting data from 622 infants, and all of the people involved in the BATSS study have done an incredible job.
[00:08:19.629] Jo Carlowe: How might your findings, Charlotte, inform future practice or influence the way we think about infant development?
[00:08:26.449] Charlotte Viktorsson: As I said, this is one of the largest infant twin studies ever conducted and, therefore, I think that our conclusions are extremely valuable for the field of infant research. As I mentioned before, we know a lot about infant behaviour on a group level, but we know almost nothing about why we see individual differences in these behaviours. Now, we know that the tendency to look at the eyes versus the mouth at five months is highly heritable and I think that future studies should focus on exploring the aetiology of more infant behaviours and abilities and how they relate to later development.
[00:08:56.930] Jo Carlowe: Just want to be clear on something. So, if the infant pays more attention to the eyes compared to those that pay more attention to the mouth, how does that seem to translate into later communication skills and learning? What…?
[00:09:11.350] Charlotte Viktorsson: So, I this case, we did find the association with later language comprehension at 14 months. So, if – the more you looked at the eyes at five months, the higher language comprehension you had at 14 months. However, that was the only link we did find in this case with later abilities. So, it does seem to be a quite independent trait, this eye-mouth index that we used.
[00:09:32.570] Jo Carlowe: And are there any implications for CAMH professionals in terms of how this translates into practice?
[00:09:39.519] Charlotte Viktorsson: At the moment, I wouldn’t say that there are. This is very new research and we don’t really know if it’s maybe related to even later development or maybe other traits that we haven’t measured. So, for now, this is new and important information for infant development, but there’s no practical implications today of these findings, I think.
[00:10:04.329] Jo Carlowe: So, where do you go next? Are you planning some follow-up research, or is there anything else in the pipeline that you can share with us?
[00:10:12.339] Charlotte Viktorsson: I do have one study in review at the moment, where I look at the heritability of sustained attention to faces in the same sample of twins. And in that study, we, kind of, zoom out from looking at specific parts of the face, to analysing gaze behaviour to faces in general. So, you can keep an eye out for that one.
[00:10:30.650] Jo Carlowe: Okay, fantastic. Charlotte, finally, what is your take home message for our listeners?
[00:10:36.149] Charlotte Viktorsson: I think my take home message is the importance of studying these early differences in behaviours and abilities, because it might seem insignificant, but very early deviations that are very small might turn into huge differences later on in life, throughout the development. So, I think it’s very important that we do study and understand these early individual differences and, of course, their relation to later outcomes.
[00:11:00.720] Jo Carlowe: Fantastic. Thank you ever so much. For more details on Charlotte Viktorsson, please visit the ACAMH website, www.acamh.org and Twitter @acamh. ACAMH is spelt A-C-A-M-H and don’t forget to follow us on your preferred streaming platform. Let us know if you enjoy the podcast, with a rating or review, and do share with friends and colleagues.