What separates Walmart America from Amazon America? Apparently, a household income of $75,000.

Walmart may still be shopped by more Americans than any other retailer, but it's lost the top spot among households with incomes of $75,000 or more to Amazon and even has slipped behind Target among that group, according to a new survey by Shullman Research Center.

Even if Amazon is visited more by upper-income adults than Walmart, Walmart still outsells it by a huge margin, with U.S. sales of $264 billion last year compared with Amazon's global sales of just under $50 billion.

The online survey, fielded between Oct. 30 and Nov. 9, found 62% of U.S. adults say they shopped at Walmart at least once in the prior 12 months, compared with 53% who shopped online with Amazon and 46% who shopped at Target .

Among households with incomes of $75,000 or more, however, Amazon led all retailers, with 60% of respondents having shopped there the past 12 months vs. 54% at Target and 53% at Walmart. The survey combines both online and offline shoppers for multichannel retail brands.

While Amazon's share dips slightly among the super-rich with incomes of $250,000 and up, its lead over Walmart also widens there. Walmart, in fact, also slips behind Best Buy in shopping frequency among those high-income groups, as only a third of Americans with household incomes above $250,000 reported shopping there.

The survey fielded responses from a nationally representative sample of 501 adults in all income ranges and more than 1,000 additional consumers in households with incomes of $75,000 or more.

The research firm is headed by Bob Shullman, former CEO of Ipsos-Mendelsohn, who has started his own firm after leaving Ipsos last year. His survey work differs from the Mendelsohn surveys of affluent Americans, he said, in part by incorporating data from non-affluent households for context and focusing more on monthly than annual reporting.

Some of the divergence between haves and have-nots likely owes to Walmart's increased focus the past two years under U.S. CEO Bill Simon on its core customers -- households in the $30,000 to $60,000 range. Surveys by other firms, such as Consumer Edge Research, show those moves have reduced shopping by higher-income consumers at Walmart.

Even so, Walmart returned to increases in same-store-sales growth earlier this year after two years of declines, and Mr. Simon has said in recent quarterly reports that the retailer is gaining market share again broadly in the U.S. retail market.

"As always, we are focused on helping our core customer save money so they can live better," said Walmart spokesman David Tovar in an email. "Last week, we had our best ever Black Friday events."

But it's clear Amazon represents Walmart's biggest threat, Mr. Shullman said.

"If you actually listen to consumers, many of them don't differentiate between brick-and-mortar and digital today," he said. "Three or four years ago, they did. ... Amazon has made it extremely easy to buy. And higher-income people clearly understand the value proposition Amazon has."

At least one factor winning high-income households is Amazon Prime, a subscription service that includes free two-day shipping on all orders and free streaming video, either as part of a Kindle Fire purchase or for a $79 annual fee. A substantial 22 % of adults with household incomes over $250,000 reported they're Amazon Prime members, Mr. Shullman said.

The first Shullman Monthly Luxury and Affluence Pulse released today also had some interesting if puzzling findings indicating the upper middle class likes ads more than anyone else does. People in households making more than $75,000 tend to have more recall and interest in ads than households overall or than households with incomes over $250,000.

For example, 80% of people in the 75,000-plus group recalled seeing TV ads in the past 30 days, compared with 72% of people overall and 71% of people with incomes of $250,000 or more. Similar patterns occurred in all other media types and when people were asked if they were interested in ads they've seen.

Mr. Shullman can't explain the data yet, but said follow-up surveys would delve into the issue. One possibility -- upper-middle-class adults find advertising more relevant than poorer folks because they have money to spend and more relevant than higher-income because they're targeted more by mass advertisers.