Final answer:
The alar plate is responsible for sensory processing, as it gives rise to neurons that receive sensory input from the periphery.
Step-by-step explanation:
The function of the alar plate in the embryonic brain stem and spinal cord is related to sensory processing. During the development of the spinal cord, the neural tube splits into two distinct parts: the basal plate and the alar plate. The basal plate, located ventrally, is responsible for giving rise to motor neurons and thus associated with motor control. In contrast, the alar plate is situated dorsally and differentiates into neurons responsible for receiving sensory input from the periphery. Therefore, the posterior regions of the embryonic central nervous system, represented by the alar plate, are specifically tasked with processing sensory information.