Idiolect

   There is a well-documented case of such an instance in Théodore Flournoy,  From the Indies to the Planet Mars: A Study of a  Case of Somnambulism with Glossalalia.  This book describes how Hélène Smith produced, under various states of hypnosis and altered consciousness, drawings of plants, villages, persons, and scenery on Mars. She also produced, orally and in writings, messages in a Martian language.

   Words in phrases in Martian have a one-to-one correspondence with the words in their French translation. This fact convinced Flournoy that the drawings and texts were not "really" from Mars. Of course, due to the astronomer Percival Lowell's observation of features resembling canals on Mars that might be the work of an intelligent species, and due to the invention of radio which would make communications with intelligent Martians possible, the idea of the existence of life on Mars was very much "in the air" at the time.

   Here is the Martian language's alphabet (p. 201) and a sample Martian text (Fig 32, p. 222).

   Here are its transliteration into Latin letters and translations into French and English (p. 222):

Martian: Ramié, pondé acâmi andélir téri antéch
French: Ramie, savant astronome, apparaîtra comme hier
English: Ramié, learned astronomer, will appear like yesterday

Martian: iri é vi anâ. riz vi banâ mirax ti Ramié ni
French: souvent à toi maintenant. Sur toi trois adieux de Ramié et
English: often to you now. Upon you three farewells of Ramié and

Martian: Astané. évaï divinée..
French: Astané. Sois heureux!
English: Astané. Be happy!

    This shows that a person can produce a previously unknown language and script spontaneously in an altered state of consciousness.  An idiolect hypothesis seems quite compatible with the known details of James Hampton's life and work.

   The numbers of vowels and consonants identified by VFQ for Hamptonese are at least comparable to those of phonemic English. As of July 22, 2001, VFQ shows 13 vowels and 18 consonants for Hamptonese;  compare this to the 10 vowel and 25 consonant phonemes of English.  So Hampton's idiolect is most likely based on English.

    Martian is certainly based on French but it would not be easy to identify the correct French word from the corresponding Martian one! So even if Hampton's idiolect is based on English, its decipherment will not be a trivial task.