Left alone in a room, a group of people were given a complicated seven-piece puzzle, known as a Soma cube, and told to assemble the pieces into specific designs. One group was offered a monetary reward for each correctly assembled puzzle; another group was offered nothing. They worked at the puzzles until being told they could stop. And then the experiment really began.

Edward Deci, the research psychologist behind the study, told the subjects to read a collection of magazines while he recorded his findings. Instead of tabulating the puzzle data, he observed the subsequent behavior of both groups. The group promised payment tended to quit assembling the puzzles, picking up the magazines instead. The group offered nothing was more likely to keep trying.

“When money was used as an external reward, intrinsic motivation tended to decrease,” Deci wrote of the experiment. (Click this link to read the full paper, “The Effects of Externally Mediated Rewards on Intrinsic Motivation,” as a PDF.)

Deci’s psychological experiment precedes the invention of Facebook by 24 years and Twitter by more than a quarter of a century. But it’s even more relevant today as the influx of rewards-based campaigns by brands — such as coupons, free giveaways, discounts — changes the nature of sharing on social media. Facebook just announced “Deals,” a feature that allows brands to offer a reward to consumers willing to share their location. Major brands have signed up for the service, including Starbucks and McDonald’s.

Social media “rewards our intrinsic desires for membership and sharing as well,” writes Clay Shirky in “Cognitive Surplus.” If a substantial body of research on human motivation says people aren’t really motivated by monetary reward, why are brands taking this approach?

Rewards-Based Sharing

In part, because it works. Consumers who “like” brands on Facebook have been inundated with monetary rewards and free food. Chipotle’s Halloween social media

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campaign included free Booritos and a chance at $7,500 in cash prizes to people willing to dress up like a “horrifying processed food product.”

Consumer products behemoth Procter & Gamble recently launched Future Friendly, a campaign that offers as much as $200 in annual rewards per household for recycling, green blogging and sharing with friends.

Granted, sharing content online in social media platforms is not exactly the same as putting together a complicated puzzle, but if the core of Deci’s theory of human motivation holds true in the fragmented and chaotic environment of the social web, it raises an important question: Can sharing for sharing’s sake survive in an ecosystem that increasingly turns every sharing exchange into monetary reward?

It’s telling that a recent report proves what common sense tells us: The motivation to “like” a brand on Facebook is most often driven by monetary gain, with 40 percent saying they become fans to receive discounts and promotions. Yet only a small percentage of consumers (17 percent) say they’re more likely to buy a brand after becoming a “fan” on Facebook, according to the same survey.

Of course, there’s a longstanding gulf between what consumers say they do in self-reported quantitative studies, like the one cited above, and what consumers actually do in the real world. And, in most cases, it remains impractical to link transactional sales data to a person’s “fan” status on Facebook.

This gulf isn’t really new. Mass advertising can’t make a clean connection with sales, either. But it’s far easier to see results in the social media space — fan growth, wall posts, sharing and tweets. Even if fan numbers don’t prove deep loyalty to a brand, it’s a metric nonetheless. Although with “Deals,” this long coveted link might be easier to make.

Social Media Spend On The Rise

A consumer deciding to “like” a brand on Facebook isn’t much different from the old-school way of signaling brand affinity by, say, wearing a Coca-Cola T-shirt.

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It’s just now there’s something given in return for effectively wearing a logo T-shirt online, be it a coupon for a box of onion rings from White Castle or a $1 off coupon from Tide. And that’s one reason the deluge of rewards-based social media campaigns isn’t going to stop.

Consider that in 2010, a mere 5.9 percent of marketing budgets was spent on social media. By 2015, this should explode to 17.7 percent, according to a recent survey of CMOs by Duke University’s Fuqua School of Business.

Facebook has survived the rash of branded pages and reward-driven ad campaigns. It continues to add users at an astonishing clip. But is there a line when the commercialization of the human impulse to share becomes just too crass?

In announcing the launch of “Deals,” on its blog, Facebook noted that “today’s mobile phones allow people to connect on the go and to share interesting moments as they happen all around them.” Could Facebook users’ walls end up full of brags about freebies? Indeed, how many of us haven’t shared the details of a bargain with friends, colleagues and family. This too is a very real human impulse. The question is whether this flood of ads and rewards changes irrevocably the essential nature and ecosystem of social media today.

Meanwhile there’s a fledgling movement to take back the social web and create new environments brands can’t co-opt. Diaspora, an alternative platform that touts itself as the privacy-aware, personally controlled, do-it-all open-source social network, is the antithesis of Facebook.

As Diaspora’s founders try to build an alternative social network, Twitter is quickly adding advertisers and expects to have more than 100 by the end of the year. The micro-blogging site, which has just started publishing ads in users’ streams to execute a moneymaking corporate strategy, will now be commercialized just like Facebook.

Twitter has arguably thrived by tapping into the intrinsic human motivation to share ideas, musings and interesting links. Could the flood of ads — and, undoubtedly, rewards and coupons will be part of this — unwittingly suppress the human desire that’s driven its success?

Mya Frazier is director of trends and insights at Engauge, one of the nation’s largest independent advertising agencies. As the advertising correspondent for MediaShift, she chronicles the impact of digital, mobile and social marketing trends on content, culture and commerce. A former business journalist, she has been a staff writer at Advertising Age, the Cleveland Plain Dealer and American City Business Journals. Her work has also appeared in the Economist, New York Times and Next American City. You can follow her on Twitter @myafrazier or at myafrazier.tumblr.com.