Hermann von Helmholtz, in his 1867 Handbuch der physiologischen Optik (Treatise on Physiological Optics), argued that perception is not a passive registration of sensory data but an active process of unconscious inference — the brain automatically and involuntarily constructs hypotheses about the external world from incomplete and ambiguous sensory evidence. The idea was radical for its time: the dominant view held that perception was a direct readout of stimulus properties.
Helmholtz’s framework anticipated by more than a century the Bayesian and predictive-coding accounts of perception that now dominate computational neuroscience. The modern formulation — that the brain maintains a generative model of the world and updates it via prediction errors — is essentially Helmholtz’s unconscious inference rewritten in the language of probability theory. The hearing book’s treatment of Bayesian perception in this chapter is a direct descendant of Helmholtz’s 1867 insight.