What can young infants see, hear, and smell? Newborn infants’ sensory abilities are significant, but their senses are not yet fully developed. Many of a newborn’s innate preferences facilitate interaction with caregivers and other humans. Although vision is their least developed sense, newborns already show a preference for faces. Babies who are just a few days old also prefer human voices, they will listen to voices longer than sounds that do not involve speech (Vouloumanos & Werker, 2004), and they seem to prefer their mother’s voice over a stranger’s voice (Mills & Melhuish, 1974). In an interesting experiment, 3-week-old babies were given pacifiers that played a recording of the infant’s mother’s voice and of a stranger’s voice. When the infants heard their mother’s voice, they sucked more strongly at the pacifier (Mills & Melhuish, 1974). Newborns also have a strong sense of smell. For instance, newborn babies can distinguish the smell of their own mother from that of others. In a study by MacFarlane (1975), 1-week-old babies who were being breastfed were placed between two gauze pads. One gauze pad was from the bra of a nursing mother who was a stranger, and the other gauze pad was from the bra of the infant’s own mother. More than two-thirds of the week-old babies turned toward the gauze pad with their mother’s scent.
In order to detect external stimuli (things in the environment), sensory receptors and organs must be fully functional. In other words, in order to see you must have photoreceptors (rods and cones, the sensory receptors for light) and a fully developed eye. Sensation is merely receiving that information from the outside world. After sensation we have perception, making sense of that information - adding meaning to it. Perception refers to the interpretation of the sensory information received and happens in the brain. In other words, perception is more complicated. One of the most interesting things to examine in infants is the stimuli that are drawn to - what are babies programmed to notice and like? And how do we "ask" the nonverbal infant about what it prefers?
Sensory Development
Vision
The womb is a dark environment void of visual stimulation. Consequently, vision is the most poorly developed sense at birth. Newborns typically cannot see further than 8 to 16 inches away from their faces, have difficulty keeping a moving object within their gaze, and can detect contrast more than color differences. If you have ever seen a newborn struggle to see, you can appreciate the cognitive efforts being made to take in visual stimulation and build those neural pathways between the eye and the brain. When you glance at a person, where do you look? Chances are you look into their eyes. If so why? It is probably because there is more information there than in other parts of the face. Newborns do not scan objects this way; rather, they tend to look at the chin another less detailed part of the face. However, by 2 or 3 months, they will seek more detail when exploring an object visually and begin showing preferences for unusual images over familiar ones and for patterns over solids and faces over patterns and three-dimensional objects over flat images. Newborns have difficulty distinguishing between colors, but within a few months are able to discrimination between colors as well as do adults. Infants can also sense depth as binocular vision develops at about 2 months of age. By 6 months, the infant can perceive depth perception in pictures as well (Sen, Yonas, and Knill, 2001). When the infants begin to crawl has been found to be the best predictor of avoid depth (Richards and Rader, 1983), suggesting that experience plays a role in the development of depth perception.
Hearing
The infant’s sense of hearing is very keen at birth. The ability to hear is evident as soon as the 5th month of prenatal development. In fact, an infant can distinguish between very similar sounds as early as one month after birth and can distinguish between a familiar and non-familiar voice even earlier. Some of this ability will be lost by 7 or 8 months as a child becomes familiar with the sounds of a particular language and less sensitive to sounds that are part of an unfamiliar language.
Other senses
Newborns can distinguish between sour, bitter, sweet, and salty flavors and show a preference for sweet flavors! They are sensitive to touch and can distinguish between their primary caregiver's scent and that of others.
How do we know what the infant can see, hear, smell, or taste? While sensory receptors and organs may be formed and functional, how do know what distinctions a baby can make or what it prefers? Researchers have developed a number of techniques for exploring such things. Habituation, for example, is one such approach. When a stimulus is first presented, there is a response to it. Over time, habituation is seen - a decrease in the response to that stimulus. If the stimulus is then changed, we see a new response as dishabituation occurs. Habituation protects us from being overwhelmed and distracted by elements of the environment. When you first put on a tight shoe or an itchy shirt, it initially bothers you. But, over time, you habituate to that stimulus and no longer react to it. Observing changes in responsiveness to stimuli is one means of informing our understanding of infant abilities. The representative studies provided here demonstrate other approaches.
Visual Preference Method
According to the APA (American Psychological Association) Dictionary of Psychology, the "preferential looking technique" is ..."an experimental method for assessing the perceptual capabilities of nonverbal individuals (e.g., human infants, nonhuman animals). Infants will preferentially fixate a 'more interesting' stimulus when it is presented at the same time with a 'less interesting' stimulus, but only if the stimuli can be distinguished from one another. To minimize bias, on each trial the investigator is positioned so that he or she can observe the infant and make a judgment about which stimulus the infant fixates, but the stimuli themselves are visible only to the infant." In other words, researchers can use the time spent looking at a stimulus as a means of quantifying their attention and as a means of telling what differences they are capable of detecting. This method has been used to demonstrate that newborns are more interested in faces and face-like stimuli. This same method has been used to demonstrate that infants seem to prefer prosocial behaviors (subjects doing nice or helpful things for others) and that events that are nonsensical are more interesting.
Robert L. Fantz (1925-1981) was a developmental psychologist who launched several studies on infant perception including the preferential looking paradigm. Fantz introduced this paradigm in 1961 while working at the Case Western Reserve University. The preferential looking paradigm is used in studies of infants regarding cognitive development and categorization. Fantz's study showed that infants looked at patterned images longer than uniform images. He later built upon his study in 1964 to include habituation situations. These situations exhibited an infants preference for new or unusual stimuli.
Orienting and Tracking Responses
One of the simplest ways of testing an infant's ability to see or hear something is by presenting the infant with a stimulus and observing whether or not the infant turns its head towards this stimulus. This orienting response is a simple way to test the infant's ability to sense a stimulus. Assessing whether or not an infant can visually track a stimulus, follow that stimulus with its eyes, is another way to test what the infant can see.
High Amplitude Sucking
High amplitude sucking is a means of detecting habituation - or dishabituation. A mechanical nipple is used to measure the infant's "suck rate". When a novel stimulus is presented, suck rate increases and, eventually, they habituate to that stimulus and the rate declines. When a new stimulus is presented (and detected) the rate increases. This technique has been used to explore the ability of an infant to tell voices apart and to differentiate between similar sounds. In experiments that measure an infant's "suck rate", a mechnical nipple is used to detect the infant's response.
Visual Cliff
The visual cliff is a technique designed to determine whether or not an infant can perceive depth. The infant is tested to see whether or not it will crawl across a piece of clear plexiglass. This technique has been used to detected the ability to perceive depth in a variety of species.
Gibson, E. J., & Walk, R. D. (1960). The "visual cliff." Scientific American, 202(4), 64–71. doi.org/10.1038/scientificamerican0460-64
Macfarlane A. Olfaction in the development of social preferences in the human neonate. Ciba Found Symp. 1975;(33):103-17. doi: 10.1002/9780470720158.ch7. PMID: 1045976.
Mills, M., & Melhuish, E. (1974). Recognition of mother's voice in early infancy. Nature, 252(5479), 123–124. doi.org/10.1038/252123a0
Richards J.E. & Rader N. (1983) Affective, behavioral, and avoidance responses on the visual cliff: effects of crawling onset age, crawling experience, and testing age. Psychophysiology. Nov;20(6):633-41. doi: 10.1111/j.1469-8986.1983.tb00930.x. PMID: 6657851.
Sen, M. G., Yonas, A., & Knill, D. C. (2001). Development of infants' sensitivity to surface contour information for spatial layout. Perception, 30(2), 167–176. doi.org/10.1068/p2789
Vouloumanos, A., & Werker, J. F. (2004). Tuned to the signal: The privileged status of speech for young infants. Developmental Science, 7(3), 270–276. doi.org/10.1111/j.1467-7687.2004.00345.x
