I have a degree in Linguistic with field work in the Northwest to Slave Lake area.
I know how natives from a number of tribes talk, ie their phonology and grammar. I also know how various Midwestern dialects sound and grammatically express their thoughts. You are preaching to the choir.
The FBI has a vast linguistic data base with people to judge such matters.
It's my understanding that "preaching to the choir" means you are talking to people who already agree, so are you saying that I'm correct to suggest that the "I just learned English from the white man 15 minutes ago" accent is a put on or are you saying I'm wrong? I've never met any Indians that really talk like that, but maybe that is different with Natives in the south who have had well over 100 years longer to be "westernized" than their Northwest counterparts.
Also, concerning linguistics, are we really that confident in the "Midwestern" theory since the only people who spoke to him were hardly qualified experts. In a court of law I'd put a lot more trust in a lay person's assessment of an individual's height or weight than in someone's ability to recognize an accent or someone's lack of one.
You are the linguist, so obviously I defer to your vast knowledge of this matter.
No, Im not sure Cooper spoke with what I (or linguists) would classify as a Midwestern accent. In the sense used, "Midwestern" simply implies lack of palpable speech affects that would point to say southern, upper midwest, New Yorker, Bostonian, foreigner, or some other gross category. All speech gets filtered through the mind of the listener. Both Flo and Tina were from the east coast? They probably were saying Cooper had 'neutral' speech without any particular accent that made itself clear. To them that equals Midwestern. It's a gross characterisation saying they did not detect a particular "accent".
Rather than trying to guess what Flo and Tina meant, I would have to hear Cooper's speech to make some judgement. His idioms "get the show on the road" and "no funny business" both have the origin in the Midwest, but I'm not even sure how far one can go with that because by 1970 those idioms were almost universal in a broad swath from east coast to California and even in certain English speaking areas of Canada.
My guess is any native American raised on a reservation by other native Americans probably would have signs of that background in his or her speech. And it could be noticed.
But, everyone has an "accent" from some dialectical background. It's unavoidable. I debated that with Carr but never could get him to admit that.
We would have to have a recording of Cooper to know what his linguistic background was. Evidently no recordings of Cooper were made or exist.