What's more, the effect could become even more pronounced as mobile wallets are adopted by a broader base of consumers, and evolve to incorporate loyalty points and targeted promotions.
Read More5 things shoppers hate about loyalty programs
"People spend significantly more when they're using a credit card," said Ross Steinman, chairman and associate professor in the psychology department at Widener University. "If we take that idea and extend it to mobile payments, I would expect that to be at least in [the 12 to 18 percent] realm, perhaps a little bit more."
Cash has long been regarded as the best way for shoppers to budget, as there is a physical action associated with it. In other words, as shoppers take the money out of their wallet and count out the bills, there are multiple reminders that they're making a payment.
"If you're actually handing over physical cash, you can reflect on what it took to get that cash," Steinman said.
On the flip side, he said it's easier for shoppers to disassociate from the money they're spending when they swipe a piece of plastic. When using digital payments, shoppers are yet another step removed.
Read MoreWant to tap $3.4 trillion? Don't miss this shopper
Then, there is the "newness" of the process. As mobile wallets are first adopted, some consumers will make purchases just because of the novelty effect, Steinman added. And as the technologies evolve to incorporate more than just touch and pay capabilities—by tying in loyalty programs and targeted deals, for instance—consumers will be tempted even more by the desire to reap the rewards they are offered.
According to a recent report by Forrester, 57 percent of adult online smartphone users in the U.S. are interested in accessing loyalty program points and rewards through their mobile wallet.