Unconscious inference

[5] In the third and final volume of his Handbuch der physiologischen Optik[6] (1856–1867, translated as Treatise on Physiological Optics in 1920-1925, available here), Helmholtz discussed the psychological effects of visual perception.

[7]We are unable to do away with such optical illusions by convincing ourselves rationally that our eyes have played tricks on us: obstinately and unswervingly, the mechanism follows its own rule and thus wields an imperious mastery over the human mind.

Helmholtz's second example refers to theatrical performance, arguing that the strong emotional effect of a play results mainly from the viewers' inability to doubt the visual impressions generated by unconscious inference: An actor who cleverly portrays an old man is for us an old man there on the stage, so long as we let the immediate impression sway us, and do not forcibly recall that the programme states that the person moving about there is the young actor with whom we are acquainted.

Through our eyes, we necessarily perceive things as real, for the results of the unconscious conclusions are interpretations which "are urged on our consciousness, so to speak, as if an external power had constrained us, over which our will has no control".

As Daniel Gilbert has pointed out, "Helmholtz presaged many current thinkers not only by postulating the existence of such [unconscious inferential] operations, but also by describing their general features".

[17][18] However, several recent authors have since approached Helmholtz's conception under a variety of headings, such as "snap judgments",[19] "nonconscious social information processing",[20] "spontaneous trait inference",[21] "people as flexible interpreters",[22] and "unintended thought".

[23] Siegfried Frey has pointed out the revolutionary quality of Helmholtz's proposition that it is from the perceiver, not the actor, whence springs the meaning-attribution process performed when we interpret a nonverbal stimulus: By failing to distinguish appearance from reality, the psychology of expression merely perpetuated a fallacy deeply ingrained in everyday language: with unswerving belief in our perceptions, we routinely call the other person’s expression what is, in plain truth, our own impression of her or him.