A recent series of studies has found that public speakers consistently overestimate their audience's emotional state, both positive and negative, because they focus on the most expressive faces, according to the Harvard Business Review.

In one experiment, researchers showed subjects images of groups of up to 12 people and asked them to judge these people's average emotional state; while each picture was calibrated at certain levels of emotion, participants consistently overestimated the emotional state of the groups. In this experiment, the researchers found that the bigger the group, the more people would overestimate, and that they were more sensitive to negative than positive emotions.

In the second experiment, researchers asked participants do the same thing but tracked their gaze with an eye-tracking apparatus. They found that, as in the past experiment, participants overestimated the emotional state of the audience, and that their gaze consistently fell on the most expressive faces in the audience, indicating that these faces were the ones the participants were judging the whole audience by.

The researchers said that people giving presentations can get a better read on how they're doing by looking not only at the most expressive people but at the whole audience.