A new study published online this month in Public Opinion Quarterly revealed that negative advertisements targeting President Obama during the GOP campaign in 2008 depicted him with very dark skin to appeal to viewers’ racial biases, The Independent reported. After 126 advertisements from the 2008 presidential campaign were analysed, it was found that images of opponents in negative ads were manipulated to shadow or wash out their face for dramatic effect.

In Senator John McCain’s campaigns that alleged the president’s involvement in criminal activities, Obama’s skin appears very dark. As the election drew nearer, images of Obama in McCain’s campaigns became gradually darker, the study revealed. It cannot be concluded whether this was part of their strategy. The authors of this study–Solomon Messing of the Pew Research Center; Maria Jabon, a software engineer who works for LinkedIn; and Ethan Plaut, a postdoctoral fellow at Stanford University–confirmed that the darker images of Obama affected the way viewers perceived him.

These findings highlight politicians’ attempts to appeal to people’s prejudices and come at a time when US presidential hopeful and Republican candidate Donald Trump has been severely criticised for his hate speeches against ethnic and religious minorities.