Final answer:
Vision is the least functional sense at birth. Newborn infants have a developed sense of smell and can prefer their mother's voice but have comparatively underdeveloped vision, preferring high-contrast patterns.
Step-by-step explanation:
The sense that is the least functional at birth is vision. While touch, taste, and smell are quite developed at birth, newborns' vision is considerably less developed. Newborn infants show a preference for faces and can differentiate between their mother's voice and a stranger's. A newborn's sense of smell is also strong, allowing them to distinguish their mother's scent from others. However, their ability to see is not as advanced, and they have a preference for high-contrast patterns primarily because their visual acuity and color perception are not fully developed yet.
The five senses are hearing, sight, taste, touch, and smell. Each of these senses provides critical information about the surrounding environment to the brain, with different parts of the nervous system dedicated to processing each type of sensory input. The senses of taste and smell are closely interconnected, relying on direct interactions with chemical substances in the environment. Meanwhile, the sense of vision develops as the newborn adapts to the light and visual stimuli in their environment after birth.