Stylized improvisation patterns were common among mothers singing lullabies during the Renaissance. This improvisation style was imitated by Renaissance composers commemorating the Nativity of Christ, according to Groves Dictionary of Music. Something was going on in the child-rearing culture that made for great pitch sensitivity as these babies grew up. Perhaps the lullaby's were styled so that both the pitch side of the brain and the rhythm/words side of the brain were informed together through a mutual association with pitches, rhythms and nonsense syllables.
After composing many songs with this two syllable system, and sensing how naturally the songs composed themselves, I realized that the mother's improvised lullaby probably did the same thing instinctively. The lullaby would assign two syllables such as "La" and "lu" to strong and weak beats of a gentle rocking rhythm, with a third syllable, "Lay" being used to mark the end of a phrase or section:
8 La
.............6 lu
...................5 La
.................................3 lu
.......................................2 La
..........................................................1 Lay
...................................................7 lu
With this improvising style, interval sets transposed diatonically would teach the baby's ear that 'this set is like this set'. An outlay of interval structure, a kind of 'pitch grid', would become very strong in the baby's mind, reinforced by the syllables and rhythm:
................6 lu . . . . . .. . . . . . . . . .(major second)
5 La.............5 La...............5 Lay
......................................3 lu . . . . . . . . . . . . . . . .(minor third)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(two sets a perfect fifth apart)
..........................................2 lu . . . . . . . . . . . . . . . .(major second)
.........................1 La ..............1 La................1 Lay
.................................................................6 lu . . . . . . . . . . . . . . . .(minor third)
Many adults singing in choirs today cannot sing in tune. They received instruction in solfege as children, know the names of the notes, the keys, the time signatures, etc., ala left brain, but cannot sing in tune ala right brain. Stylized two-syllable songs can improve the adult singer's intuitive tuning sense somewhat, but the best time to introduce these songs is in early childhood.
I was asked by my church choir director to work with one of the singers in the choir who was having some pitch problems. He had received solfege instruction in school as a child. I was having him sing 'da-di' patterns after me, to help him improve his tuning, and he exclaimed, "How I wish someone like you had taught me when I was young!"
Recently I was explaining and demonstrating my teaching system to a singer trained in opera. She said the same thing. "I wish I had had this kind of instruction when I was young." Here was a trained singer who felt that she could have benefited from this.
Real musical understanding and aptitude has less to do with naming names of pitches than it does with the ability to mentally hear them as distinct yet related entities, long before naming them. After the pitch relationships have been intuitively clarified through two-syllable singing, solfege can be useful, but it is not essential. Solfege introduced too early in childhood, without sufficient prior singing experience, can be detrimental to the singing ear.