Psychology2016

324 CHAPTER 8

Although most infant sensory abilities are fairly well developed at birth, some

require a bit more time to reach “full power.” By using techniques such as the habituation

method discussed earlier, researchers have found that the sense of touch is the most well

developed, which makes perfect sense when one realizes how much skin-to-womb con-

tact the baby has had in the last months of pregnancy. The sense of smell is also highly

developed. Breast-fed babies can actually tell the difference between their own mother ’s

milk scent and another woman’s milk scent within a few days after birth.

Taste is also nearly fully developed. At birth, infants show a preference for sweets

(and human breast milk is very sweet) and by 4 months have developed a preference

for salty tastes (which may come from exposure to the salty taste of their mother’s skin).

Sour and bitter, two other taste sensations, produce spitting up and the making of horri-

ble faces (Ganchrow et al., 1983).

Hearing is functional before birth but may take a little while to reach its full poten-

tial after the baby is born. The fluids of the womb first must clear out of the auditory

canals completely. From birth, newborns seem most responsive to high pitches, as in a

woman’s voice, and low pitches, as in a man’s voice.

The least functional sense at birth is vision. The eye is quite a complex organ.

to Learning Objective 3.4. The rods, which see in black and white and have

little visual acuity, are fairly well developed at birth, but the cones, which see color and

provide sharpness of vision, will take about another 6 months to fully develop. So the

newborn has relatively poor color perception when compared to sharply contrasting

lights and darks until about 2 months of age (Adams, 1987) and has fairly “fuzzy” vision,

much as a nearsighted person would have. The lens of the newborn stays fixed until the

Figure 8.5 Six Motor Milestones
Shown here are (a) raising head and chest—2 to 4 months, (b) rolling over—2 to 5 months, (c) sitting up with support—4 to 6 months, (d) sitting up without
support—6 to 7 months, (e) crawling—7 to 8 months, and (f) walking—8 to 18 months. The motor milestones develop as the infant gains greater voluntary con-
trol over the muscles in its body, typically from the top of the body downward. This pattern is seen in the early control of the neck muscles and the much later
development of control of the legs and feet.

a.

d.

b.

e. f.

c.

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