Alert (?): A new(?) or regional(?) negative usage

[Rudolph C Troike]

I just picked up this inquiry on my e-mail from U Penn, and thought I'd
pass it along to see if anyone has any further enlightenment.
        Rudy

---------- Forwarded message ----------
Date: Mon, 16 Jul 2001 15:09:25 -0400
From: sela at babel.ling.upenn.edu
To: penguists at babel.ling.upenn.edu
Subject: interesting use of "don't"

I'm wondering if anyone out there can shed some light on the following:

 I am curious about the phrase "So don't I" as a way to respond in the
 positive to a statement.  I have a feeling it may be acceptable  only
 regionally (New England).  To give an example of its use:

 1  A:  I really like cherry flavoured yogurt.
    B: Oh, so don't I.  (meaning I like it too.)
    C:  So doesn't Mary.
  but
   *B: Oh, so do I not. (or any formation of the phrase without the
 contracted form.)

 1 makes perfect sense to me, I have even caught myself using it.  It
 also makes sense to the friends I've asked from my hometown in Rhode
 Island.   My British boyfriend thinks it makes no sense at all.

  You can also use the negative contraction  in a positive response like this:

 A:  I'm running in the roadrace tomorrow.
 B: Really? So aren't I.(meaning so am I)

 where the verb doesn't agree with I (probably because it only works with
 the contracted form and there isn't a contracted form of 'am not' that
 is acceptable to me)

 any thoughts as to why this can be?

Suzanne  LaBelle