http://www.seobook.com/archives/001996.shtml
Here’s an excerpt from this research:
There is a direct connection to the thalmus to the amygdala which allows the amygdala to emotionally react to a sensory impulse before the neocortex can evaluate the input, thus when the neocortex does logically evaluate something you may already have that emotional bias worked into the equation, and thus try to justify it as being right…I think this was also mentioned in Blink, but is an interesting point.
I take this to mean that people often make a subconscious, emotional decision about whether they like something before they start to evaluate it consciously. As a big part of website optimisation is about trust, it raises the question of how to use colour, design, layout, images etc to create a sense of trust that people will pick up on.