SAT Text Structure and Purpose Question

Curious about how people visually perceive objects in their dreams, Stephen LaBerge and team recruited lucid dreamers — people aware that they’re dreaming as it’s happening — for a research study. These participants were reliably able to signal when they had entered a dream state; the team then observed participants’ eye movements as they slept. The smoothness with which participants’ eyes tracked objects in their dreams closely matched how sighted people who are awake visually track objects around them, suggesting to the team that the brain perceives dream objects as the product of something other than pure imagination. Which choice best states the function of the underlined portion in the text as a whole?