Purpose: Variability in the timing of infant developmental milestones is poorly understood. We used a twin analysis to estimate genetic and environmental influences on motor development and activity levels in infancy. Method: Data were from the Gemini Study, a twin birth cohort of 2,402 families with twins born in the United Kingdom in 2007.…

This study reports on the development of new motor and behavioural indicators for recognizing symbolic acts among infants. Following five infants between the ages of 6 and 18 months and their ability to use an object in novel way yielded four levels of action, based on the number of objects and actions combined in each symbolic act. Employing…

The infant brain may be predisposed to identify perceptually salient cues that are common to both signed and spoken languages. Recent theory based on spoken languages has advanced sonority as one of these potential language acquisition cues. Using a preferential looking paradigm with an infrared eye tracker, we explored visual attention of hearing…

Fragmented sleep is common in infancy. Although night awakening is known to decrease with age, in some infants night awakening is more persistent and continues into older ages. However, the influence of fragmented sleep on development is poorly known. In the present study, the longitudinal relationship between fragmented sleep and psychomotor…

The current study examined the relations between individual differences in attention to emotion faces and temperamental negative affect across the first 2 years of life. Infant studies have noted a normative pattern of preferential attention to salient cues, particularly angry faces. A parallel literature suggests that elevated attention bias to…

Saccade latency is widely used across infant psychology to investigate infants' understanding of events. Interpreting particular latency values requires knowledge of standard saccadic RTs, but there is no consensus as to typical values. This study provides standard estimates of infants' (n = 194, ages 9 to 15 months) saccadic RTs under a range of…

The development of theory of mind (ToM) in infancy has been mainly documented through studies conducted on a single age group with a single task. Very few studies have examined ToM abilities other than false belief, and very few studies have used a within-subjects design. During 2 testing sessions, infants aged 14 and 18 months old were…

Infants' motor skill development triggers changes in parent-infant interactions, exploration, and play behaviors, particularly during periods of locomotor transitions. We investigated how these transitions reorganized infants' and mothers' explorations of spatial layouts. Thirteen infants and their mothers were followed biweekly from the age of 6…

This research examined the child, parent, and family conditions under which attachment disorganization was related to both level and change in externalizing behavior during preschool among a community sample. Using the ordinary least squares regression, we found that attachment disorganization at 12 months significantly predicted children's…