If you thought Google's level of insight into our online activities was already verging on frightening, then beware: Now the search giant is literally tapping into people's brains.

In conjunction with MediaVest, Google partnered with biometrics research firm NeuroFocus to study how people respond to InVideo ads and how those ads complement traditional banner ads. To do so, NeuroFocus measured people's brain responses, via sensors on their heads, while they viewed the ads. They also took into consideration factors such as pupil dilation and skin response, reports Mediaweek.

Based on a study of 40 participants, NeuroFocus determined that InVideo ads are more compelling than other forms of advertising in terms of attention, emotional engagement and effectiveness. Those scores improved further when users were presented with both InVideo and corresponding banner ads.

Earlier this year, Google began selling ads that appear inside videos on sites in its publisher network. The program features InVideo ads -- a format developed for YouTube in which semi-transparent overlays appear at the bottom of the video player -- and text overlay ads that are contextually targeted based on signals that appear both in the video and on the page.