As has been determined on the basis of X-raying
and cineradiography, there are two rather different articulations that
produce virtually the same acoustic pattern perceived as "American R".
Both are postalveolar approximants, but the active articulator (the tongue)
behaves differently and takes a different shape in each
case.
The retroflexed variant
is made with the tongue tip raised towards the postalveolar area; the
middle part of the tongue is lowered and almost flat. In the "bunched" version the body of the tongue
assumes the shape of a ball; the tip is lowered and "tucked away" underneath,
while the arched middle part rises towards the postalveolar/prevelar area of
the roof of the mouth. In either case there is
also some pharyngeal constriction (more for the buched variety) as the
root of the tongue approximates the wall of the pharynx.
I'm not sure if these terms are easier, but I
hope they are more precise than the forwarded description.
Many Americans use one of these varieties either
predominantly or to the complete exclusion of the other, but it has been
reported that some speakers can shift from the one to the other even within a
single phonetic realisation of /r/. Reportedly, the variants are so similar
acoustically that native speakers of American English cannot distinguish them
by ear.
Piotr
Piotr sez:
"In either case there
is also some pharyngeal constriction"
I think, in my case, there is a lot of 'pharyngeal constriction'. When I
have described my Rs (I have at least two), I describe a constriction at the
back of the throat to describe them -- almost a glottal stop; this is my first
R. The other R is smooth, with no constriction at all. This last R is the one
where the tongue is mostly at the bottom of the mouth, with the tip resting
against the lower teeth.
But, as Piotr explains, there is the other R. When I exaggerate this
R, this one can be curled back almost 360 degrees, where you try to put the tip
of your tongue somplace way way back into the mouth of the throat. Well, more
like someplace beyond 180 degrees, but the description suffices. And
yes, there is a constriction in the throat. There is sum'n funny in my
speech.
Curiously, to the satisfaction of my high-school-Spanish-teacher sister, I
can do the pero/perro distinction in Spanish. One of them hits the alveolar
ridge, the other one does not. I forget which spelling means 'but' and which
means 'dog', but I can do the trilled one with a single clean alveolar tap.
Mark.