Mahler used heterophony (the "indistinct unison") as far back as the first
published version of the First Symphony and the original (MS) version of
the Second, hence from the mid-1890s on.

It usually takes the form of overlaying ornaments or momentary doublings in
contrasting timbres on a relatively continuous melodic line; occasionally
the main melodic line is itself fragmented as well.

Locally it serves to highlight specific details of pitch or rhythmic
contour in the line; it also has a long-range role.  Recurring material
in sectional forms (i.e., the rondo-like third movement of the Second)
is often recomposed upon returning, with enriched heterophony as well as
in more complex textures.

The issue of Eastern influence is another matter, however, since by the
time of Mahler's reported encounters (confirmed or not) with either written
transcriptions or recordings of Asian music, heterophony both combined with
and independent of melodic fragmentation had already become an essential
part of his orchestral language.

I discussed this matter at some length in an undergradate Honors thesis
on the structural role of instrumental color in the first 4 symphonies
of Mahler written as far back as 1961.  Should have published some of it....

Joel
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