4 Early Research Approaches

Following Francis Galton’s publications, a wave of synesthesia research ensued in the late 19th and early 20th centuries in which individual cases were in part meticulously described. Between 1880 and 1920, approximately one hundred pieces were published every decade. As had been the case with Eugen Bleuler, research interest focused on identifying shared characteristics between color perceptions, since despite obvious differences there were evidently certain regularities: a connection between pitch and brightness was proposed frequently. There were also scattered reports of a connection between volume and size, volume and brightness, and pitch and size. There were various explanatory approaches: on one side, certain scientists were of the opinion that synesthesia had a pathological origin (Claviere 1889); it was assumed that there was either a faulty circuit between the respective sensory centers (Pedrono 1882) or a kind of insufficient differentiation between sensory centers (Coriat 1913). Another theory postulated that different sensory impressions shared characteristics through which synesthetic perception was conveyed (Bleuler 1881, Féré 1892).

Synesthesia disappeared again from the focus of scientific interest in the late 1940s because it had not been possible to objectively measure the phenomenon, and introspection (i.e. self-description) was no longer recognized as a method of collecting data in experimental psychology. The number of publications consequently decreased. Between 1930 and 1940, only 30 pieces of writing were published; in the ensuring years it was even less (Marks 1975).