Dear 100 Hour Board,
Frequently in product testimonials in commercials and infomercials, while the person is talking about why the product is good, I see them wiggling their head side to side. Is it a studied thing in psychology that waving one's head in a slight "no" manner is perceived as sincerity?
P.S., If, while working this question, you are in the position of trying to tell someone something, and try the sincerity-signaling-head-wiggle maneuver, let me know whether you think it helped them feel your sincerity or if you think they looked like it made them feel weird seeing you wiggle your head like an infomercial shill :)
Funny side story: Indians move their heads side to side to mean "yes". I noticed minnow's family doing this and I was SO CONFUSED because their heads would be giving what I thought was the universal sign for "maybe" but they'd be saying "yes definitely". I still get confused because I'll ask minnow a question and he'll move his head side to side and I'll be thinking "why isn't he sure about that?"
As you can imagine, body language is very important in advertisements because it's important in human psychology. Nodding or shaking your head while listening to/writing down ideas can influence how much you agree with them (source), and as people tend to mirror others' actions (source), advertisers may hope that some unconscious mirroring may increase positive feelings for the product. Another study, using movie clips of people nodding and shaking their heads, found that "the nodding head motion significantly increased ratings of subjective likability and approachability relative to those of the shaking or control conditions, whereas the shaking motion did not influence the ratings. Furthermore, it was shown that a nodding head motion of the computer-generated models primarily increased likability attributable to personality traits, rather than to physical appearance. We concluded that head nodding motion is treated as information regarding approach-related motivations and enhances perceived likability" (source).
However, I haven't found anything about people shaking their heads to signify "no" as a positive. In all studies, shaking one's head either led them to be less convinced by arguments or have no impact, unlike nodding "yes". I can see advertisers choosing to include moving one's head from side to side (in the American "maybe" Indian "yes" way), because a "yes" nod might be too obvious. But that's the only explanation I can think of.
-guppy of doom