Could you tell which pictures, which depict how the vowel chart is positioned inside our mouth, are accurate?

Question

Ok, we all know that the vowel chart diagram is drawn like this

Wikipedia

Ok, that is the model, but how the vowel chart is positioned inside our mouth or how the tongue in the reality is placed according to the diagram?

We got the X-rays of Daniel Jones of 4 extreme point [i, u, a, ɑ] as showed in the following diagram:

Wikipedia Ok, It seems that the X-rays of Daniel Jones could be drawn as the followings:

Wikipedia

Now, here is quite confusing?

Some websites interpret how the vowel chart is positioned inside our mouth like the following (Interpretation 1):

Source

Other websites interpret how the vowel chart is positioned inside our mouth like the following (Interpretation 2):

Source

However, other websites interpret like this (Interpretation 3):

Source

So, which Interpretation is accurate (Interpretation 1, 2 or 3)?

I think the Interpretation 1 is the most accurate because it is pretty close the X-rays of Daniel Jones. But I am not sure about that.

In the Interpretation 2, it seems that the author implies the position of the tongue of /i/ & /a/ is way too close to the front of the mouth. However, in the X-rays of Daniel Jones, the position of /i/ & /a/ is a bit retracted & is not too lose to the front of the mouth

Seem there is a lack of standard of how to depict how the vowel chart is positioned inside our mouth. That is causing a lot of confusing, right?

Answer 1

The defined standard for cardinal vowels is the Jones performances. IPA is loosely related to Standard Cardinal Vowels, but the IPA letter < i > can be used for a wide range of phonetic values ranging from Cardinal Vowel 1 to something rather close to [ɪ]. "Accuracy" implies a standard (that is, what thing does the chart accurately reproduce?), and it isn't clear what standard you are interested in. I am inclined to think you mean "correctly reproduces Daniel Jones' tongue positions", but perhaps you mean "accurately reflects the vowels [i,u] etc. in English", or else in Spanish, or maybe Dresden German.

What you would need to do is map the vowel dots in the x-rays to a coordinate system, using some fixed bony structure as a reference point such as the upper incisors and the palatine process). Unfortunately, the "interpretation" graphs don't scale well to the x-rays, though Interpretation 1 is the best of the three (the other two are schematizations, not drawings of x-rays). In the x-rays, the box that surrounds the extreme vowels [i,ɑ] is twice as long horizontally as it is high, but the box that contains the "vowel space" in picture I1 is only 1.25 times as long as it is high. In fact, I1 looks like Peter Ladefoged, and may be accurate as a representation of Peter Ladefoged. However, I1 is only a vowel space: it does not give specific points for vowel locations, so it does not at all represent the 4 tongue positions in the Jones x-rays.

The other drawings are substantially off. So despite the fact that specific vowel positions are not given in I1, the schematized vowel space given there is at least consistent with where specific cardinal vowels are likely to be produced.

Answer 2

You cannot really project the whole vowel trapeziod into a single picture of the mouth because the shape of the mouth and the tongue actually change as you move through the chart. So any single picture such as the three above will be inaccurate.

The chart really depicts relative positions of the highest position of the tongue with the edges being the extremes thought possible. So any projection will be just a rough schematic suggestion. But 1 is obviously the closest to some semblance of reality.