The myths of supermarket selling: Are the big food retailers reading us all wrong?

Cheap tricks: as shoppers, we are less influenced by price than we think we are. Habit is a more powerful influence (Alamy)

You think you know how you shop. You think you're conscious of the decisions you make in the 28 minutes and 30 seconds you spend, on average, navigating the aisles of your local supermarket. You're not. Because when you grab that trolley, you turn into a hungry hamster in a laboratory maze filled with rewards and obstacles – and only the men in the white coats know what you're really thinking.

Simeon Scamell-Katz could be described as a professor of supermarkets. A schoolleaver who started his career on the shop floor aged 16, he is now one of the world's leading consumer analysts. He has spent decades watching us, filming us and tracking our eyeballs. To the supermarkets, where we spend £160m on food every day, this kind of information is gold, yet, surprisingly, Scamell-Katz says, the "big four" and their friends are really bad at selling the products a vast industry spends millions developing.

"It's a slow-moving industry and these companies make huge profits, so why do anything differently?" Scamell-Katz says from his home in rural Norfolk, which is, ironically, relatively free of supermarkets. "They're very bad at learning."

But money is no longer falling into the laps of supermarkets. This week, Tesco revealed declining sales and profits at its UK stores, threatening 20 years of supremacy. It also announced £1bn of investment in revamped stores. Its executives might do well to read our minds if they are to reverse the chain's fortunes. Regardless, for those of us who care less about bottom lines, Scamell-Katz's research, published in his new book, The Art of Shopping, offers fascinating insights into the way we think. It also reveals aisle-wide gaps in what we – and retailers – think we know.

Price is everything

Do you know the cost of a pint of milk? Probably not. Supermarkets are built on pound signs but how much do we care, or even notice? Like most shoppers Scamell-Katz talks to, a woman he interviewed for a recent television documentary claimed to keep an eye on prices. Technicians equipped the shopper with a device that tracks the movement of the eyeball to determine what the subject is looking at. They then sent her on a normal, 30-minute shop. "She was stunned to discover that she only looked at the price label twice," Scamell-Katz says.

One of the reasons for Tesco's latest trouble is the failure of its Big Price Drop campaign, which cost £500m but has failed to attract enough shoppers to make up for the cuts. What Tesco and its price-war competitors often forget is the extent to which we are guided through aisles not by our wallets but by habit or subconscious thought.

"Generally we make broad assumptions about price using other visual clues," Scamell-Katz explains. "If you're buying baked beans you might look for a tin with an aquamarine colour and a black tombstone-shaped label because that [Heinz] is the brand you usually buy. You simply don't notice anything else."

Eye level is buy level

Supermarkets make big money from the fees they charge brands to place a product. Location is key and fees vary accordingly. It had been assumed shoppers are more likely to notice a product at eye level, at about 1.6 metres from the floor. Traditionally, supermarkets charged more for shelves at this level.

Using eye-tracking technology, Scamell-Katz found this to be a myth. "We naturally look lower than eye level," he says. "Somewhere between waist and chest level." Crucially, waist level is also hand level. When Scamell-Katz handed this evidence to his then client, Procter & Gamble, the company began negotiating for lower shelves, initially causing bemusement among the supermarket suits. It worked, and sales increased.

Another myth is that products are more visible towards the ends of aisles, or on the terminal block of shelves known as the "gondola end", where discounted or new products are often placed. But a study for Unilever showed shoppers activate their eyes towards the middle of an aisle, once they've located themselves in, say, the cereal category. Here, we identify, without realising it, what are known as "signpost brands". These are the best-known products, such as Coca-Cola, which signal the presence of a category, such as soft drinks.

One of Scamell-Katz's clients was Guinness, a signpost brand for stout, which, research showed, customers were often skipping to get to lagers or bitters. When Guinness paid for 4ft cardboard pint glasses to be positioned at either end of the stout shelves, sales of all drinks in the category increased by 23 per cent and by 4 per cent for all beer.

Put the bread at the back

Anyone who finds the mustard has hotfooted it across two aisles will know about the importance of supermarket geography – and the frustration that comes with change. "Supermarkets used to think moving categories around forced customers to pay attention and consider purchases more carefully," Scamell-Katz says. "But the evidence shows that if you disrupt people, they buy less." Shoppers build maps of stores, allowing us to ignore aisle markers and even shopping lists. We use memory and signpost brands to navigate as if on auto-pilot. We are armed only with a "mission", be it to stock up for the family for a week, or grab a few bits for a solo dinner. Increasingly, we do the latter, yet stores want us to cover ground in the hope we will be distracted from our mission and buy more. That's why essentials such as bread or milk are often placed deep into a supermarket.

It doesn't work. A study at a petrol station store showed that placing lunchtime staples such as sandwiches at the end of an aisle bursting with potential impulse buys failed because shoppers would not be diverted, but would be annoyed, and more likely to go elsewhere. "If you put products at the back people go straight there and ignore stuff on the way," Scamell-Katz says. "If you make it easy for the shopper on a mission to buy bread, they'll come back, and are more likely to do their main shop there as well."

Choice is good

The average supermarket stocks around 80,000 lines of 25,000 available products. The average British household uses 300 products in a year, about 150 of them regularly. Do supermarkets really need to invest so much to offer us such choice? No. Yet they do it because in consumer surveys we say we want choice (and because they make money from listing fees from each product). But, again, we don't know our own minds. In Italy, Danone commissioned research into sales of its dozens of yoghurts. It then told the retailer to do the unthinkable and cut the range by 40 per cent. It did, and monitored the results. Only 15 per cent of shoppers surveyed noticed anything different. Of the rest, most thought there were more options. Meanwhile sales increased by 20 per cent. "By offering too much choice, the range becomes invisible through complexity," Scamell-Katz explains. "By reducing the range, options have the chance to become visible."

Shoppers are loyal

If we are loyal to, say, Sainsbury's or Hob Nobs, it's usually in the same way a rabbit is loyal to a nine-year-old girl. We don't care that much. "We're brand-habituated, not brand-loyal," Scamell-Katz says. "There are some brands we genuinely love but usually we find something that's good enough, to avoid the hassle of making new choices. That looks like loyalty and brands will work on strategies and advertising to retain and reward that loyalty, when they should just be making it as easy as possible to buy."

This is another illustration of the power of habit. Part of the reason we form habits is the pleasure it gives us. A study at UCL in 2006, cited by Scamell-Katz, found that trying new things employed upper regions of the brain. Falling back on the familiar, meanwhile, fires up the brain's pleasure centres. Scientists suggest we have evolved to be cautious, or unadventurous. That, too, looks like loyalty. As for store loyalty cards? "That's just about data-gathering," Scamell-Katz says. Which is a whole other story.

The Art of Shopping - How We Shop and Why We Buy by Simon Scammell-Katz (LID, £18.99)