methods would be available (a discussion with the pediatrician or see, for example, the article on sleep training). = normal sleep = Sleep hygiene should be improved = it is recommended to seek help (pediatrician, sleep counselling). Maternal sensitivity Maternal sensitivity plays a particular role in the relationship with the infant and for favorable emotional development. This means being attentive to the infant's behavioral expressions, not misinterpreting the infant's expressions because of one's own moods, reacting immediately to the situation and finding a response that is appropriate to the context and the expressed needs. A secure attachment is promoted through empathetic and adequate as well as prompt responses. In accordance with their basic needs, infants show an inborn behavior of seeking closeness to the mother – or to another primary caregiver – and thus in turn foster an attachment. When separated from the mother, infants protest by crying and by body movements. Other Wearing has a calming effect on infants. A 2013 study showed that infants placed in a cradle cried and kicked more often and had an increased heart rate (so the infants were stressed), while those picked up and carried by the mother while walking around calmed down significantly. The effect of being held motionless in the arm was intermediate between that of being carried around and that of being put down. That carrying (e.g., in a baby sling) makes infants more content and makes them cry less had already been shown in a randomized study in 1986. For infant feeding, breastfeeding is recommended by all major infant health organizations. Many airlines refuse boarding for all babies aged under 7 days (for domestic flights) or 14 days for international flights. Asiana Airlines allows babies to board international flights at 7 days of age. Garuda Indonesia disallows all babies under the age of 14 days to board any flights. Delta Air Lines allows infants to travel when they are less than 7 days old when they present a physician travel approval letter. Skywest will not allow an infant less than 8 days old on board. Behaviour Emotional development Attachment theory is primarily an evolutionary and ethological theory whereby the infant or child seeks proximity to a specified attachment figure in situations of alarm or distress for the purpose of survival. The forming of attachments is considered to be the foundation of the infant/child's capacity to form and conduct relationships