Yes, their personalities swap.

Batman, had strapped himself into the machine, feeling the energy’s surging throughout himself. The longer he sat there the more painful it all became, it felt like each one of his nerves were being poked and prodded, zapped and beaten, burned and drowned… it wasn’t pleasant, that was for sure. He closed his masked eyes in pain, trying not to scream, until it all went away. The pain subsided quickly, and he opened his eyes again, still in the Mad Hatter’s laboratory. Tetch was still tied up ****, and judging from a clock on the wall, only a few minutes had passed.

Batman felt… funny. Not exactly like fuzzy funny, a little bit weird funny, but like, more “ha ha” funny, you know? He, like, startled to giggle and chuckle a little, as he picked himself up and out of the funky chair device. He began to feel very amused until he heard some serious grunting coming from the other room. “What, you masta-bait in’ in there?” He said out loud, not really caring what anyone thought. He heard a plea for help and decided to saunter over to the next room, not afraid to strut his stuff.

Batman spotted the totally hawt Harley Quinn struggling in her funny chair, and strutted over, feeling sexy in his suit. “Need some help, hun?” He asked sarcastically, sitting himself on one of the armrests. He lifted up Harley’s helmet.

Dr. Quinzel looked curious at Batsy as he playfully removed her straps. “Batman,” she pondered, “what’s gotten into you? You’re suddenly acting all silly and, frankly, dumb.” She sternly looked him up and down as she got up, her stance strong and intimidating, in a way.

“Whatsit to ya?” Batman asked incredulously, before deciding to think on it. “Anyways, umm, imma guess that, like, Mad Hatty’s machine went fritzo when I popped in, and because it worked by altering and attuning brainwaves, I think I dunno I didn’t work on it, it must’ve warped our minds so that, like, our personality traits were swapped!” Tired of talking so much, Batman began doing cartwheels, going “wheee” the whole time.

Harley’s face immediately begat horror, realizing what this meant. “While I became a serious person, focused on what’s important, you took on my former traits of acting like a, well, silly bimbo! Oh god, this could be bad!”