Most of us will feel that a high pitch and exaggerated length, perhaps also the vowel i (English ee) indicate smallness, while low pitch and length and the vowels a, o, u (English oo) indicate large size…Large or small size, or intensity may be expressed by variations of sound. Thus New Perce, an Indian language spoken in Idaho, changes n to l to indicate smallness; Dakota has many words in which s changes to sh or z or j, indicating greater intensity…undoubtedly the particular kind of synesthesia between sound, sight and touch has played its role in the growth of language.
Gyorgy Kepes, Language of Vision, 1944, 167.