A Black Friday study in which 50 shoppers hit the sales wearing sweat-sensing bracelets has offered a glimpse into the thought processes that determine when we drop our dough.

The bracelets, developed by the Massachusetts Institute of Technology Media Lab, measure movement, body temperature and electrodermal activity — barely noticeable changes in skin sweat levels that signal stress and excitement. They’re the newest market research tool for stores battling over limited consumer bucks.

“Shoppers have more retail choices than ever before,” said John Ross, chief executive officer of Shopper Sciences. “It’s good for consumers, but it’s a tremendous challenge for marketers.”

Market research, a field once dominated by surveys, is increasingly turning to technology to get more reliable reactions from consumers. Because despite all the brainy logic that goes into planning purchases, shoppers often follow their instincts — a response analysts are tracking in sweat, facial expressions and even brain activity.

“It’s a proxy for how our brains work,” Ross said of using biometrics in addition to pre- and post-shop surveys. “It’s a more holistic way of doing shopper-based research, because we’re measuring the full cognitive system that humans use when they make decisions.”

Ross said Black Friday — a day famous for long lines, scary stampedes and now pepper spray — can generate a range of emotions in shoppers.

“But the prevailing one in our study was excitement,” he said.

Most of the bracelet-clad shoppers had a positive experience, with 80 percent spending more than they had planned and more than half buying presents for themselves.

Shopper stress was linked more to line length than concerns about missing out on deals.

“The data shows the highest stress level occurred while shoppers were waiting for the store to open,” Ross said. “Once the store was open, shoppers were really happy — until they had to wait in the checkout line.”

Surprisingly, shoppers showed similar stress patterns whether they were shopping in stores or online.

“You would think sitting in an armchair wearing a robe waiting for a site to go live would be far less stressful,” Ross said. “Even though you don’t have the pushing and shoving, shopping purely online tends to be pretty stressful, too.”

People who shopped in stores and online were the least stressed and ended up spending more – a perk of being prepared, said Ross.