Does racial prejudice play a role in questions about Barack Obama's citizenship, a topic much in the news given today's birth certificate news conference? Yes indeed, suggests one recent psychology study.

President Obama on Wednesday released the long-form version of his 1961 birth certificate from Hawaii, a bid to further refute citizenship questions raised most recently by Republican presidential aspirant Donald Trump. "The President believed the distraction over his birth certificate wasn't good for the country," said White House communications director Dan Pfeiffer, in a statement.

Trump said his questioning of Obama's citizenship "had nothing to do" with race, in an interview on The View.

So, what's behind the questions about Obama's birthplace? Racial prejudice does play a role, suggests a study led by Eric Hehman of the University of Delaware in the March Journal of Experimental Social Psychology, which contrasted voter's perceptions of vice president Joe Biden, "the most comparable target" with Obama.

"The influence of racial prejudice in contemporary U.S. society is typically manifested in subtle, indirect forms of bias. Due to prevailing norms of equality, most Whites attempt to avoid appearing biased in their evaluations of Blacks, in part because of a genuine desire to live up to their egalitarian standards, but also because of concern regarding social censure," notes the study. "As a consequence, Whites' prejudice is more likely to be expressed in discriminatory responses when these actions can be justified by other factors."

So, to tease out the influence of racial prejudice on perceptions of Obama's Americanism, the researchers asked 295 students, both black and white, to evaluate the performance and "Americanism" of the two politicians in late 2009. They also included six questions, widely used in psychology, to gauge whether folks are more or less prejudiced against blacks. For example, participants were asked how strongly they agree or disagree with the statement, "I would rather not have other-race students live in the same apartment building I live in."

"Overall, as expected, White participants tended to view Obama as less American," says the study, as well as worse-performing. "Moreover, Whites higher in prejudice rated Obama as less American, and as performing more poorly as president."

However, "low-prejudice" whites tended to see Obama as more American and better performing than Biden, says the study:

Why low prejudice Whites perceived Obama as higher in Americanism and performing better than Biden is not entirely clear. One possibility is that people see presidents, as the primary national leader, as more prototypical of the group and thus more American than vice-presidents. Alternatively, the differential response of low prejudice Whites to Obama and Biden may reflect their concern with appearing nonprejudiced, particularly during a period when the election of a Black president was lauded as a sign of progress for not only Blacks but America more generally.

To test this further, the researchers looked deeper at prejudice scores among the study participants. They found, "higher prejudice predicted Whites seeing Obama as less American, which, in turn, predicted lower evaluations of his performance." Blacks meanwhile, tended to rate Obama's performance higher than Biden's, but didn't view their Americanism as significantly different.

Overall, the results support our hypothesis that negative evaluations of Obama by White participants may be racially motivated. Whites are guarded about openly endorsing the view that Blacks are less American than Whites, which may suppress overall mean differences in performance ratings and perceptions of Obama being un-American. However, bias in viewing Blacks as less American than Whites appeared to implicitly underlie Whites' negative evaluations of his performance. Also, consistent with previous research, Blacks did not demonstrate such a relationship, nor did Americanism mediate the relationship between prejudice and performance evaluations when Vice-President Biden acted as target for either Whites or Blacks. Whereas previous work has linked White prejudice with negative perceptions of Obama, the current work reveals a mechanism that may be largely responsible for this effect, Obama's non-prototypicality (largely in terms of his race) and thus reduced perceptions of his Americanism.

Psychologist Jack Brigham of Florida State University, an expert in racial attitudes research who was not part of the study, says, "the results strongly support a role of racism in the birther movement." He adds the racial attitude survey questions used in the study represent legitimate measures of prejudice used in psychology. (The Project Implicit effort offers a similar online implicit racial attitudes test for folks wanting to try a similar test on themselves.)

The results support recent research that prejudice expresses itself in American society in non-overt ways, sometimes in attitudes not even consciously held by people, says the study, which concludes:

Finally, many in the media have speculated that current criticisms of Obama are a result of his race, rather than his agenda. We believe that the current results are an empirical demonstration that this is sadly the case. As the United States approaches important decisions regarding issues such as economic reform, health care, and overseas military interventions, the intrusion of racial attitudes in the evaluation of political leaders' performance is ironically inconsistent with what many believe to be "American."

On that note, USA TODAY asked Hehman to comment on today's long-form birth certificate release, in light of his team's study. Here is his email reply: