Updated

How many times have you gone shopping, knowing exactly what you need, only to leave the store with more than you had on your list?

Stores use all kinds of subliminal tactics proven to make you shop longer and buy more stuff — stuff that you don't necessarily want or need.

For example, that "buy-one-get-one-free" candy bar you casually dropped into your cart while waiting on the checkout line…or those shoes you splurged on because you saw them on display when you walked into the store and couldn't get out of your mind.

Environment has a powerful influence over our behavior and stores are no exception, says Art Markman, a professor of psychology at the University of Texas and author of "Smart Thinking."

While retailers aren't known to use advanced methods of subliminal messaging, Markman says they can manipulate the environment to make it easier for customers to think about particular products, and to increase the chances of an impulse purchase.

"When products are easily available, easy to reach, and in view, then people are more likely to buy them," he explains.

Some of those common tactics are:

  • Music: Many stores use music to influence our shopping experience."Grocery stores may play slower, less popular songs because they want us to focus on the task at hand — not get excited and start singing along," says Jordan Gaines, a science writer and Ph.D. candidate at Penn State College of Medicine. On the other hand, she says, "Fast-paced music, like at a clothing store, encourages us to flit about from rack to rack, looking at more clothes in a shorter amount of time." 
  • Store Primers: Gaines says things like flowers and fresh produce placed near the entrance of a store are designed to set the tone for the rest of the shopping experience.  While priming is not proven to be an effective tactic, Markman says, "products at the front of the store influence what people will think about during their trip." For example, it might get you thinking about a significant other, which might increase your chances of buying a present for them. 
  • Point of Purchase Items: Many of the items that are placed at the checkout lane are true impulse buys, says Markman. Things like candy, batteries, and magazines are designed to appeal to the goals of a large number of people. "Willpower is a limited resource, and so the longer you have to stand in front of the candy, the harder it is to resist." 
  • Smell:  Smell can be a great cue for memory. "Many stores have taken to cooking in open areas to allow the scent of cooked food to diffuse through the store," Markman says. "When you first encounter a smell, it serves as a reminder that you might want to make a particular purchase." Some clothing stores also use what's known as "scent branding." Gaines says stores like Abercrombie & Fitch will employ companies to develop a distinctive scent for their stores. "It works a bit like classical conditioning, where we'll pair the scent with the store, and if we have a good shopping experience, or enjoy the product, we're more likely to go back for more," she says. 
  • Imagery:  "One reason why clothing stores like American Apparel use sexual images in their stores is that it increases the arousal of shoppers, which also improves their evaluations of the clothing," says Markman. 
  • Online:  "Retailers want to be in your environment," says Markman. "The shorter the distance between a thought and an action, the more likely it is that someone will perform that action. Retailers who send you emails are trying to shorten that distance. The issue is not emotion so much as ease."

In general, Markman doesn't think subliminal advertising is very different from overt advertising. "Manufacturers and retailers are trying to manipulate your information environment and change the way you think in order to affect what you buy," he explains.

Likewise, Gaines says the best way to avoid falling victim to subliminal messages is to go into the store armed and ready to recognize it. "If you make a list and stick to it, you'll find it harder to fall prey to all the different ways stores try to trick us."