Every presidential election year, CNN or another news network pulls together a group of voters, usually undecideds, and asks them to watch a debate with devices known as "perception analyzers."

You probably know what they are, even if you don't know what they're called. Perception analyzers are the dial-equipped devices that voters or likely voters can hold and use to register their response to what each candidate says during the course of a live or televised event. The end result is a minute by minute graph of how the group collectively thought about what each candidate said. If the concept eludes you, here's all you have to know: Because the test subjects are measuring approval and disapproval with a dial, moving the dial to 50 is considered a neutral response. The further away from 50, the more intensely the focus group participant feels. The highest approval score is 100, and the max disapproval measure is zero.

This year, one of the many questions hanging over the presidential election is what millennial voters actually care about? What the issues are that will galvanize this group and bring them to the polls? After Monday night's debate, two professors — who ran a live experiment with a small group of 18- to 25-year-old Hofstra University students equipped with perception analyzers — think they may have some revealing clues.

Based on a perception analyzer-assisted focus group, many young people seem to care about race, racial tensions in the country and questions about race, equity and criminal justice. This segment of the debate registered the highest levels of voter interest overall. But while almost all the students seemed to pay close attention to the race portion of the debate, black students registered stronger reactions than white students did on their dials. And when the debate conversation turned to foreign affairs, the entire group's interest fell off a cliff. Technically, most did not or hardly moved their dials to register any disapproval or approval at all.

"What we saw very clearly," said Charlton McIlwain, an associate professor of media, culture and communication at NYU and a co-investigator on the debate experiment with Philip Dalton, an associate professor of rhetoric at Hofstra University, "was that both black and white participants tended to like what Hillary Clinton was saying when she was talking about race and they tended to not like or to like less what [Donald] Trump was saying when he was talking about race. But in both instances, the African Americans were much stronger, they registered greater magnitude of like and dislike of what they heard the candidates say."

There's more. "When Clinton talked about the scourge of racial profiling, white participants liked what she was saying but black participants really liked what she was saying," McIlwain said in an interview late Monday night. "And when Trump was talking about bringing back stop and frisk, white participants didn't like that but black participants really, really did not like that (see the video up top). This reflects a larger tendency for people of color to care more deeply about these issues."

That's true of older and middle-age Americans. But millennials are the most racially and ethnically diverse generation of Americans in U.S. history. A lot has been written overstating the degree to which this diversity has rendered racism a relic of the past. The debate focus group would seem to indicate that a little more moderation and humility may be in order when it comes to describing the racial ideas and attitudes that millennials harbor, too.

That said, black and white students who participated were united in a lack of interest in foreign affairs.

Other big moments: There was a sharp turn downward in approval ratings when Trump talked about Clinton, the "presidential look" and stamina. A lot of the students were interested in the segment during which the candidates discussed taxes, and registered elevated approval for Clinton's call for the rich to pay their fair share. Trump also did well when he made mention of the nation's infrastructure and education needs.

"But in next breath when he started talking about cutting taxes, there was a sharp decline across the board," McIlwain said.

On tax policy, there was also a small racial divide. Trump's approval ratings with white students dropped to just below 50 when he talked about the importance of cutting taxes and how this generates jobs, but black students registered slightly stronger disapproval for this idea, giving him scores that ranged from 40 to 35.  That, of course, put both groups of students on the negative or disapproval side of the dial.

Students across racial groups responded positively to Clinton's mention of Trump stiffing workers and companies.

Those are the focus group's basic findings. Young people care about race relations, the way that race can shape policing and criminal justice. They care a little bit less but are interested in tax policy, the distribution of the tax burden, strongly disprove of overt sexism and racial profiling, and were not interested in foreign affairs. From that, McIlwain cautions that the campaigns may be able to gather some general insights about what kind of messaging could help to draw young people out to vote. But the focus group was too small to go further than that.

How small? The test group consisted of 54 Hofstra University students under age 25. About 60 percent were white, 40 percent were black, 51 percent were male and 49 percent female. Because the experiment focused on young people, Democrats were overrepresented.

To secure a victory in November, Democratic nominee Hillary Clinton needs this diverse and growing group. (Depending how you define the term millennial, this is a group that now makes up nearly a third of the electorate. This is true if you include everyone between ages 18 and 35.) And Trump would not be hurt by young voter support, either. Trump's mostly white voter coalition skews older. So, the racial differences in the way that students responded and the fact that most were deeply engaged during the discussion on race (depicted in the images above), is intriguing.