Racial attitudes have not improved in the four years since the United States elected its first black president, an Associated Press poll finds, as a slight majority of Americans now express prejudice toward blacks whether they recognize those feelings or not.

Those views could cost President Obama votes, the survey found, though the effects are mitigated by some people's more favorable views of blacks.

Racial prejudice has increased slightly since 2008 whether those feelings were measured using questions that explicitly asked respondents about racist attitudes, or through an experimental test that measured implicit views toward race without asking questions about that topic directly.

In all, 51 percent of Americans now express explicit anti-black attitudes, compared with 48 percent in a similar 2008 survey. When measured by an implicit racial attitudes test, the number of Americans with anti-black sentiments jumped to 56 percent, up from 49 percent during the last presidential election. In both tests, the share of Americans expressing pro-black attitudes fell.

"As much as we'd hope the impact of race would decline over time ... it appears the impact of anti-black sentiment on voting is about the same as it was four years ago," said Jon Krosnick, a Stanford University professor who worked with AP to develop the survey.

'We've also seen backlash'

Most Americans expressed anti-Hispanic sentiments, too. In an AP survey done in 2011, 52 percent of non-Hispanic whites expressed anti-Hispanic attitudes. That figure rose to 57 percent in the implicit test. The survey on Hispanics had no past data for comparison.

The AP surveys were conducted with researchers from Stanford University, the University of Michigan and NORC at the University of Chicago.

Experts said they were not surprised. "We have this false idea that there is uniformity in progress and that things change in one big step. That is not the way history has worked," said Jelani Cobb, professor of history and director of the Institute for African-American Studies at the University of Connecticut. "When we've seen progress, we've also seen backlash."

Obama has tread cautiously on the subject of race, but many blacks have talked openly about perceived antagonism toward them since Obama took office. As evidence, they point to events involving police brutality or cite bumper stickers, cartoons and protest posters that mock the president as a lion or a monkey, or lynch him in effigy.

'It will take more generations'

"Part of it is growing polarization within American society," said Fredrick Harris, director of the Institute for Research in African-American Studies at Columbia University. "The last Democrat in the White House said we had to have a national discussion about race. There's been total silence around issues of race with this president. But, as you see, whether there is silence, or an elevation of the discussion of race, you still have polarization. It will take more generations, I suspect, before we eliminate these deep feelings."

Overall, the survey found that by virtue of racial prejudice, Obama could lose 5 percentage points off his share of the popular vote in his Nov. 6 contest against GOP challenger Mitt Romney. But Obama also stands to benefit from a 3 percentage-point gain due to pro-black sentiment, researchers said. Overall, that means an estimated net loss of 2 percentage points due to anti-black attitudes.

The poll finds that racial prejudice is not limited to one group of partisans. Although Republicans were more likely than Democrats to express racial prejudice in the questions measuring explicit racism (79 percent among Republicans compared with 32 percent among Democrats), the implicit test found little difference between the two parties. That test showed a majority of both Democrats and Republicans held anti-black feelings (55 percent of Democrats and 64 percent of Republicans), as did about half of political independents (49 percent).

Obama faced a similar situation in 2008, the survey then found.

The AP developed the surveys to measure sensitive racial views in several ways and repeated those studies several times between 2008 and 2012.