One interesting aspect of vision is the occasional borderline overlap between contrasting sensory perceptions. For instance, we often find transmodal bridges, transitions and interactions between vision and hearing - a perceptual phenomenon known as synaesthesia. Synaesthesia may evoke certain qualities and meanings, simultaneously or in succession: Some humans may see a colour while hearing a particular word; others may hear a specific tone when viewing the colour blue, a plethera of other combinatorial sensory assocations also exist. Synaesthesia resembles this transfer of sensoric qualities and meanings within perceptual modalities of art, music and poetry. Neuroscientific visual imaging has posited certain areas in the brain where this rare mixing of senses may take place.
Sound symbolisms and synaesthetic comparisons are widespread throughout literature. Several sensory modalities share qualities such as intensity, brightness or acoustically associated meanings. In this way, methaphors can be relatively freely transmitted between the senses. The Romantic poets interpreted synaesthetic perceptions as borderlines of the senses and described them as transitions between the single faculties of art. They were evidently very interested in these associations. This was different from the reflections of poets of the 18th century, who were interested in the diversities of the faculties of art such as painting, music, poetry. Synaesthesia happens through synchronous combination and concatenation of one sense modality with several other sense modi.
This essay proceeds in six steps: It shows how the cooperation of synaesthetic qualia with hidden and multiple meanings has always played a major role for the inner qualities of a picture of art.