Hi Milan,
The research is simply trying to determine the effectiveness of including the logo in search results as opposed to not including it. We're trying to make a case for inclusion.
The result could be quantitative. The presence of the logo enables a searcher to more easily identify returned instances of the brand.
The result could also be qualitative. The presence of the logo enhances brand promotion, and that's a priority for the client.
As to where relevant research is published, I wish I knew. I've been looking mostly on marketing research sites, and I'm not finding exactly what I need.
Eddie