This week, New York Times columnist Frank Bruni asked a very revealing question: Why is the American public so focused on Joe Biden’s age, when Donald Trump is almost as old and has a far less healthy lifestyle and physique? It’s a good point. For the moment, let’s set aside all of our thoughts about policies and values associated with the two men (to the extent that our imaginations can stretch that far). Which of them is more likely to be physically thriving in 2028, a trim 85-year-old man who eats well and at least up until now has been getting regular daily exercise, or an overweight 82-year-old man who has spent the last few decades sitting around eating junk?

So why do we care about Biden’s age but not Trump’s?

Bruni mentions geriatric specialist Rosanne Leipzig, who suggests that Biden’s language reads as “old.” He uses words and phrases like “malarkey” and “God love ya” and “c’mon man,” which feel dated. And that theory makes sense, for the small fraction of Americans who actually pay attention to Biden’s speech patterns. (I hadn’t realized “c’mon man” was elderly-talk. I must be getting up there too!) Meanwhile, she says that “Trump’s rebel pose reads young.” Maybe so. Also, as Bruni points out, Trump does his best to disguise his age with hair dye and cosmetics, whereas Biden looks his age.

But I think Bruni himself hits on a better theory, and I’m going to back it up with science.

Way back in the 1950s and 1960s, psychologist Daniel Berlyne dedicated his research career to the features of things that draw our attention: sharp contrasts, disorder, novelty, surprisingness, and so on. In art and music – and in things we see and hear more generally – these features can interest and excite us, and their opposites (order, familiarity, expectedness) can reassure us and calm us down. “Interest” and “excite” in this context can be positive (an opportunity that we want to be sure to notice) or negative (a threat that we’d better not miss), but in either case, our bodies respond.

I’ve spent the last year or so writing a book that shows how Berlyne’s work is also a factor in politics and social movements. The same features that matter to us when we see or hear things also matter when we think about things. Sharp contrasts like us/them, life/death, and before/after become part of our mental representations of the things described that way. The same goes for intensity, order/disorder, surprisingness, and the other attention-getting features Berlyne mentions. When we call that object to mind, those aspects are especially salient to us. They stick out.

Back to Bruni’s theory. Biden’s age is definitely relevant, and every time the media focuses on others’ aging issues – Dianne Feinstein, Mitch McConnell – it reminds us that a person can be too old for an important job. This fits with the intensity or magnitude family of what I’m calling “salience markers” – his age is outside the usual parameters of what we expect, and not in a good way.

Donald Trump, however, is a walking, talking, package of salience markers. He specializes in extremes, disorder, and unexpectedness. Every time he violates the conventions for how a politician is expected to talk, he sets off physiological responses in his thrilled supporters and his anxious detractors.

As Bruni puts it, “With Trump, it is always thus: The frequency of his outrages and volume of his vices guarantee that no single flaw stands out as it should. It’s just another ingredient in a gumbo of God-help-us.”

Now, as I mentioned above, reassuring features are also salient. Probably a good reason that Biden was elected in 2020 was the strong desire that many American had for “back to normal” after the Trump presidency. Biden can lean into these features if he campaigns for re-election. He does things conventionally, respecting the existing systems. He cares about order, unity, bridging divides. He’s familiar. And that’s all reassuring.

Or at least, it’ll be reassuring if we are reminded of them. The media may not care about that. News outlets need to draw attention too, so they focus on things that are more exciting or worrisome. With Biden, that’s his age. With Trump, that’s everything he ever does.