Transactions and Proceedings of the New Zealand Institute/Volume 40/Meeting 4, Paper 1
In vol. xxxii of the "Contemporary Science Series," entitled "Hallucinations and Illusions," may be found a short account of the somewhat obscure phenomenon of coloured hearing. For the benefit of those to whom the subject may be unfamiliar, I may explain that coloured hearing consists of the involuntary mental association of colours with sounds, or, to quote the scientific definition in Dr. Forel's work on hypnotism, "There is still one other sight, a mental vision—viz., the repercussion of these optical stimuli of the visual sphere in other associated areas of the cortex of the cerebrum. There are people who are able to see sounds coloured, inasmuch as they always associate certain colours with certain sounds or vowels." The special colour-sensations associated with particular sounds always remain constant in the same individual, but the relation is purely individual, and not referable to any known general law.
Letters of the alphabet (more particularly the vowel-sounds), notes of musical instruments, and numerals call up colour-sensations in the minds of persons possessed of this faculty, whether the sound of the letters. &c., be actually heard or only mentally presented.
It is found that a certain percentage of persons is possessed of this peculiarity, and that it is sometimes hereditary.
This sensation is designated a photism or chromatism by Professor Gruber, who has conducted some experiments with several subjects of the "hallucination," as it is described in the first-mentioned work. He tells us that few people can remember when their chromatisms began; and that deep tones or vowel-sounds seem generally to be associated with dark colours, and sharp tones or high-sounding vowels with lighter-colour sensations. The coloured alphabet which I have prepared in accordance with my own observations will show corroboration of the latter statement, the letter O being associated with deep-blue, while I and E are white and yellow respectively. Letters of the alphabet and numerals are, in my experience, productive of colour-impressions, but there are no distinct sensations with regard to music. Of the letters, the colours of the vowels are most prominent, a single vowel in a word often producing a colour-impression which will subordinate all the colours of surrounding consonants to itself. Thus, in considering the word "stop," the dark-blue of the vowel O predominates over all the other colours. The colour of a consonant is frequently modified by the colour of an adjoining vowel; in fact, the various colours represented by the different letters composing a word tend to modify each other in a greater or less degree. For example, in the word "book" the dark-blue associated with the letter O is the predominating colour in the word. The letter B is in my mind connected with varying shades of green. As the adjoining vowels are dark in hue, the green of the B will be dark-bluish-green. On the other hand, in the word "been" the two E's, which are yellow, cause the B to appear of vivid leaf-green. In another word, "bite," the juxtaposition of the I (white) renders the B dull-green in colour.
I may add that, while some persons experience coloured hearing as a fully developed objective sensation, I have it merely as a spontaneous mental association of colour with sound.
The account from which I obtained some information on this subject concludes with the statement that it is doubtful whether the occurrence is pathological or physiological. While I have made some conjectures, I will not trouble you with these, merely mentioning the fact that, while my own sense of colour is not, so far as I know, defective, I come of a family in which several cases of colour-blindness exist.