Bottom-up processing is analysis that begins with the sensory receptors and works up to the brain's integration of sensory information. ... From the top down, we use preexisting knowledge or expectations to guide our perception and send our senses looking for stimuli that support those expectations.
Sensation is the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment. ... Bottom-up processing is sensory analysis that begins at the entry level, with information flowing from the sensory receptors to the brain.
I would say that the answer is A sensation..