In most cases, the way the perceiver decides what the observed nonverbal behaviours mean to him or her is a fully automatic process of inference initiated inside the viewer as soon as another person comes in sight. The discovery of this odd form of information processing dates back to 1867 when Hermann von Helmholtz, the eminent German physicist whose research assistant Wilhelm Wundt became the founder of academic psychology, coined the term unbewusster Schluss (unconscious conclusion) in order to account for the way in which people arrive, on the basis of nonverbal cues, at opinions about each other.
The formation of visual impressions, Helmholtz realized, is achieved primarily by unconscious judgments, the results of which ‘can never once be elevated to the plane of conscious judgments’ and thus ‘lack the purifying and scrutinizing work of conscious thinking’. In spite of this they are, Helmholtz noticed, ‘urged on our consciousness, so to speak, as if an external power had constrained us, over which our will has no control’. And he drew attention to the truly astonishing fact that once formed, the results of unconscious judgments are so impervious to conscious control, so resistant to contradiction that they are ‘impossible to get rid of’ and ‘the effect of them cannot be overcome’. So whatever impressions this unconscious inference process leads to, they strike ‘our consciousness as a foreign and overpowering force of nature’. Which, one could add, is why ‘seeing is believing’, and why, when in everyday language we refer to an expression exhibited by another person, we really describe our own impression of her or him.