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Already at a very early age, infants preferentially attend to social stimuli. Although this is believed to be important for later social cognition and learning, little is known about the aetiology of infant social attention and associations to later abilities. In this thesis, I used eye tracking to study the influence of genes and environment on individual differences in different aspects of social attention, and developmental outcomes across different domains in toddlerhood in relation to both typical and atypical development. In Study I, the influence of genes and environment on the preference for looking at eyes versus mouth (eye-mouth-index) was assessed in 5-month-old twins. The eye-mouth-index was highly heritable, and a stronger tendency to look at the eyes was associated with later language comprehension. In Study II, sustained attention to faces was assessed in the same sample of infants, and found to be moderately heritable. Longer sustained attention was associated with more socio-communicative behaviours in toddlerhood. In Study III, videos of children interacting were shown to 18-month-olds with and without an elevated likelihood of autism. At specific time intervals in the videos, there was a significant difference in gaze allocation between the toddlers who did and did not receive an autism diagnosis later in childhood. The findings of this thesis suggest that both sustained attention to faces and eye versus mouth preference are heritable, meaning that young infants may select their environment based on their genotype, by looking at different aspects of a scene or a face. Being exposed to different types of input might influence later development, and these results indicate that social attention is associated with later social and communicative abilities, as well as later autism. In summary, this thesis contributes to the understanding of early social attention and how different aspects of this phenomenon are related to later development., Att selektivt titta mot ansikten är en grundläggande mänsklig egenskap, som anses vara en viktig del av den sociala utvecklingen hos barn. Genom att titta på andra människor får man information om deras känsloliv, intentioner och kommunikativa signaler. Trots den viktiga funktionen av social uppmärksamhet vet vi väldigt lite om etiologin bakom individuella skillnader i hur man tittar på andra människor, och huruvida sådana skillnader kan kopplas till senare social och kommunikativ utveckling. I den här avhandlingen har jag använt mig av ögonrörelsemätningar för att studera hur barn tittar på sociala stimuli. I Studie I och II bestod deltagarna av fem månader gamla enäggs- och tvåäggstvillingar, vilket gör att man kan undersöka hur ärftligt ett visst beteende är. I Studie I undersökte vi om tendensen att titta på ögon (jämfört med mun) är ärftlig, genom att visa barnen videor av en kvinna som sjunger, pratar och ler mot kameran. Resultaten visade att ärftligheten av att titta på ögon jämfört med mun var hög, och att en tendens att titta mer på ögonen vid fem månaders ålder var associerad med högre språkförståelse vid 14 månaders ålder. I Studie II undersökte vi om benägenheten att upprätthålla uppmärksamhet mot ett ansikte är ärftlig, genom att visa bilder på leende och neutrala ansikten. Tiden det tog, i medeltal, att titta på ett ansikte innan barnet tittade bort visade sig vara ärftligt och associerat med socio-kommunikativa förmågor vid 14 månaders ålder. I Studie III bestod deltagarna av barn som har en nära familjemedlem med autism, och som därför har en större sannolikhet att själva utveckla autism jämfört med den generella befolkningen. Vid 18 månaders ålder fick barnen se videor med två äldre barn, där en pojke ber en flicka om att få en leksak som hon håller i, men där flickan vägrar att ge leksaken. Det visade sig att barnen som senare diagnosticerades med autism tittade betydligt mindre på flickans ansikte efter att pojken bett om leksaken, jämfört med b

BackgroundFrom birth, infants orient preferentially to faces, and when looking at the face, they attend primarily to eyes and mouth. These areas convey different types of information, and earlier research suggests that genetic factors influence the preference for one or the other in young children. MethodsIn a sample of 535 5-month-old infant twins, we assessed eye (relative to mouth) preference in early infancy, i.e., before neural systems for social communication and language are fully developed. We investigated the contribution of genetic and environmental factors to the preference for looking at eyes, and the association with concurrent traits and follow-up measures. ResultsEye preference was independent from all other concurrent traits measured, and had a moderate-to-high contribution from genetic influences (A = 0.57; 95% CI: 0.45, 0.66). Preference for eyes at 5 months was associated with higher parent ratings of receptive vocabulary at 14 months. No statistically significant association with later autistic traits was found. Preference for eyes was strikingly stable across different stimulus types (e.g., dynamic vs. still), suggesting that infants' preference at this age does not reflect sensitivity to low-level visual cues. ConclusionsThese results suggest that individual differences in infants' preferential looking to eyes versus mouth to a substantial degree reflect genetic variation. The findings provide new leads on both the perceptual basis and the developmental consequences of these attentional biases.

When observing other people during naturally paced and dynamic interactions, it is essential to look at specific locations at the right time to extract a maximum of socially informative content. In this study, we aimed to investigate the looking behavior of typically developing toddlers and toddlers later diagnosed with autism when observing other children interact. The sample consisted of 98 toddlers; 22 in a low-likelihood of autism group, 60 in an elevated likelihood of autism group who did not receive a subsequent diagnosis, and 16 in an elevated likelihood group who did receive an autism diagnosis. Participants performed an eye tracking task at 18 months of age and were assessed for diagnostic outcome at 36 months. The video stimuli consisted of two children interacting, where a boy reaches out for a toy and a girl refuses to give it to him. The low likelihood group showed an expected increase in ratio of looking at the girl’s face after the boy requested the toy, as compared to before (t(21) = -3.337, p = .003). Toddlers with later autism showed a significantly lower ratio of looking at the girl’s face during this time window, as compared to the other groups (F(2,91) = 3.698, p = .029). These findings provide new leads on how social gaze may be different in children with autism in everyday life (e.g., kindergarten), and highlight the need of studying the dynamics of gaze on short time scales.

Background Measures based on pupillometry, such as the pupillary light reflex (PLR) and baseline pupil size, reflect physiological responses linked to specific neural circuits that have been implicated as atypical in some psychiatric and neurodevelopmental conditions. Methods We investigated the contribution of genetic and environmental factors to the baseline pupil size and the PLR in 510 infant twins assessed at 5?months of age (281 monozygotic and 229 dizygotic pairs), and its associations with common genetic variants associated with neurodevelopmental (autism spectrum disorder and attention deficit hyperactivity disorder) and mental health (bipolar disorder, major depressive disorder and schizophrenia) conditions using genome-wide polygenic scores (GPSs). Results Univariate twin modelling showed high heritability at 5?months for both pupil size (h2?=?.64) and constriction in response to light (h2?=?.62), and bivariate twin modeling indicated substantial independence between the genetic factors influencing each (rG?=?.38). A statistically significant positive association between infant tonic pupil size and the GPS for schizophrenia was found (??=?.15, p?=?.024), while there was no significant association with the GPS for autism or any other GPSs. Conclusions This study shows that some pupil measures are highly heritable in early infancy, although substantially independent in their genetic etiologies, and associated with common genetic variants linked to schizophrenia. It illustrates how genetically informed studies of infants may help us understand early physiological responses associated with psychiatric disorders which emerge much later in life.

Twin studies can help us understand the relative contributions of genes and environment to phenotypic trait variation, including attentional and brain activation measures. In terms of applying methodologies such as electroencephalography (EEG) and eye tracking, which are key methods in developmental neuroscience, infant twin studies are almost nonexistent. Here, we describe the Babytwins Study Sweden (BATSS), a multi-method longitudinal twin study of 177 MZ and 134 DZ twin pairs (i.e., 622 individual infants) covering the 5−36 month time period. The study includes EEG, eye tracking and genetics, together with more traditional measures based on in-person testing, direct observation and questionnaires. The results show that interest in participation in research among twin parents is high, despite the comprehensive protocol. DNA analysis from saliva samples was possible in virtually all participants, allowing for both zygosity confirmation and polygenic score analyses. Combining a longitudinal twin design with advanced technologies in developmental cognitive neuroscience and genomics, BATSS represents a new approach in infancy research, which we hope to have impact across multiple disciplines in the coming years.

Twin studies can help us understand the relative contributions of genes and environment to phenotypic trait variation, including attentional and brain activation measures. In terms of applying methodologies such as electroencephalography (EEG) and eye tracking, which are key methods in developmental neuroscience, infant twin studies are almost nonexistent. Here, we describe the Babytwins Study Sweden (BATSS), a multi-method longitudinal twin study of 177 MZ and 134 DZ twin pairs (i.e., 622 individual infants) covering the 5−36 month time period., Article The Babytwins Study Sweden (BATSS): A Multi-Method Infant Twin Study of Genetic and Environmental Factors Influencing Infant Brain and Behavioral Development Terje Falck-Ytter1,2,3, Linnea Hamrefors1,2, Monica Siqueiros Sanches2,4, Ana Maria Portugal2, Mark Taylor5, Danyang Li2,6, Charlotte Viktorsson1, Irzam Hardiansyah2, Lynnea Myers2,7,8, Lars Westberg9, Sven Bölte2,10,11, Kristiina Tammimies2,6 and Angelica Ronald12 1Development and Neurodiversity Lab (DIVE), Department of Psychology, Uppsala University, Uppsala, Sweden, 2Center of Neurodevelopmental Disorders (KIND), Centre for Psychiatry Research; Department of Women’s and Children’s Health, Karolinska Institutet and Stockholm Health Care Services, Stockholm, Sweden, 3Swedish Collegium for Advanced Study (SCAS), Uppsala, Sweden, 4Center for Interdisciplinary Brain Sciences Research, Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA, USA, 5Department of Medical Epidemiology & Biostatistics, Karolinska Institutet, Stockholm, Sweden, 6Astrid Lindgren Children’s Hospital, Karolinska University Hospital, Stockholm, Sweden, 7Department of Nursing, Gustavus Adolphus College, St. Peter, Minnesota, USA, 8Clinical Pediatrics, Department of Women’s and Children’s Health, Karolinska Institutet, Stockholm, Sweden, 9Department of Pharmacology, Institute of Neuroscience and Physiology at the Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden, 10Child and Adolescent Psychiatry, Stockholm Health Care Services, Stockholm, Sweden, 11Curtin Autism Research Group, Curtin School of Allied Health, Curtin University, Perth, Western Australia, Australia and 12Department of Psychological Sciences, Birkbeck, University of London, London, UK Abstract Twin studies can help us understand the relative contributions of genes and environment to phenotypic trait variation, including attentional and brain activation measures. In terms of applying methodologies such as electroencephalograp