The reception of Wagner’s music as physically affecting, sound that manipulates the bodies of listeners, took place within a context of research into human and animal physiology. From reflex mechanisms to sense energies, the physiological response to art brought about new understandings of ‘physiological aesthetics’ in figures from Herbert Spencer to Thomas Huxley and Francis Galton, with a corresponding ‘physiological music theory’ applied by Ernst Mach and Hermann von Helmholtz. This led to various efforts at quantification of ear acuity and the role of the auditory nerve.

In the shadow of decadence, critical evaluation of works like Tristan and Tannhäuser traverse the spectrum from appreciation (‘bliss of the spinal cord’) to anxiousness (‘Wagner increases exhaustion’). Against these claims, Wagner’s numerous writings on sentience (Sinnlichkeit), rooted in Ludwig Feuerbach’s philosophy of perceptual realism, were directed towards topics as diverse as a theory of performance, the role of critics, and animal testing.

Records of how to select people date back 3,000–5,000 years and there are supposed incidences in the Bible. There remain, to this day, an interest and belief in astrology despite there being little evidence that place and time of birth relate to any major individual difference factors. There is also still an interest in graphology, which is the belief that the dramatic differences in writing between individuals is an importantly and stable marker of personality or motivation. Study after study show there is no validity in handwriting analysis. The situation with regard to phrenology is different. The Victorians believed that the shape of the head reflected the shape of the brain which was primarily responsible for individual differences. The fanciful connect between head shape and brain location and psychological characteristics has however been revived by neuroscience and fMRI scanning. Similarly, the idea that body shape and build was a strong marker of personality has been discredited, but the modern interest in BMI and WHR has shown that these are indeed markers of different kinds of behaviour.