The human newborn’s umwelt: Unexplored pathways and perspectives

Abstract

Historically, newborns, and especially premature newborns, were thought to "feel nothing." However, over the past decades, a growing body of evidence has shown that newborns are aware of their environment, but the extent and the onset of some sensory capacities remain largely unknown. The goal of this review is to update our current knowledge concerning newborns' perceptual world and how ready they are to cope with an entirely different sensory environment following birth. We aim to establish not only how and when each sensory ability arises during the pre-/postbirth period but also discuss how senses are studied. We conclude that although many studies converge to show that newborns are clearly sentient beings, much is still unknown. Further, we identify a series of internal and external factors that could explain discrepancies between studies, and we propose perspectives for future studies. Finally, through examples from animal studies, we illustrate the importance of this detailed knowledge to pursue the enhancement of newborns' daily living conditions. Indeed, this is a prerequisite for assessing the effects of the physical environment and routine procedures on newborns' welfare.

Preparing for Life After Birth: Introducing the Concepts of Intrauterine and Extrauterine Sensory Entrainment in Mammalian Young

“…Contrary to earlier views that the embryo/fetus occupies a sensory void in utero (for references see [48]), it is now well established that there exists a wide range of stimuli that have demonstrable impacts on sensory systems as they develop (e.g., [5,30,38,39,40,41,42,43,44,46,48,49,66]).…”

“…Most sensory capabilities of newborn human infants are also advanced, but some are less mature than in ungulates. Tactile sensitivity in the lips and oral cavity supports sucking from a nipple; also, such receptors in the hands enable grasping and, distributed over the thorax, abdomen, and limbs, they underlie a capability to experience soothing touch [48,65,66,67]. Musculoskeletal control, proprioception, and vestibular function are immature at birth as movement is usually restricted to reflexive rooting, sucking, startle, grasp, and arm, leg, and neck movements [68,69].…”

“…Olfactory detection of areolar, breast, and milk odourants guides nipple location and supports the onset of sucking [70,71,72], and taste discrimination underlies preferences for breast milk as opposed to formula and sweet as opposed to sour or bitter tastes [41,67,73]. The nociceptive system is operational and generates experiences of pain in response to noxious stimulation [20,46,66], and hearing is sufficiently mature to be responsive to a wide range of sounds including parental and other voices, music sequences, and startling noises [30,74,75]. Finally, vision is somewhat immature at birth [34], indicated by uncoordinated eye movements, a limited ability to track objects, and a capability to focus only on objects at close range, specifically at 18 to 25 cm [66,67].…”

“…The nociceptive system is operational and generates experiences of pain in response to noxious stimulation [20,46,66], and hearing is sufficiently mature to be responsive to a wide range of sounds including parental and other voices, music sequences, and startling noises [30,74,75]. Finally, vision is somewhat immature at birth [34], indicated by uncoordinated eye movements, a limited ability to track objects, and a capability to focus only on objects at close range, specifically at 18 to 25 cm [66,67]. However, this short focal capability may be functionally appropriate because it would correspond to the distance between the mother’s face and the baby in her arms [67].…”

“…However, they do include gravitational, olfactory, gustatory, and thermal sensory inputs [89,90,91] and inputs from tactile sensory receptors in the muzzle and around the mouth [92,93]. This reflects the very early stages of the cephalocaudal developmental pattern of the somatosensory system, observed in most developing mammals, whereby responsiveness to touch first appears at the mouth, lips and face or snout, then extends caudally to the trunk, followed thereafter by the proximal and then the distal regions of the limbs [26,46,48,49,66]. Note that marsupial pouch young are dependent on maternal milk for all sustenance during the period of pouch occupancy, which lasts for about 190 days in the Tammar Wallaby [87].…”