Final answer:
Vision is the special sense not fully functional at birth; newborns have limited color and depth perception, which develop as they grow. Hearing and smell are more developed in infants, with preferences for their mother's voice and scent.
Step-by-step explanation:
The only special sense that is not fully functional at birth is vision. Although newborns exhibit a preference for human faces and can distinguish some colors like red, they have limited color perception, lack depth perception, and will only develop these visual abilities as they grow. In newborns, other senses such as hearing and smell are relatively more developed. For example, infants prefer hearing their mother's voice over a stranger's, and they exhibit a strong sense of smell, recognizing their mother's scent shortly after birth. All the special senses, along with general senses like touch, convert stimuli into electrical signals in the nervous system through a process known as sensory transduction.