Most Distinguishable Monophthongs/Vowels?

Question

I was listening to the 8 Primary Cardinal Vowels and 10 Secondary Cardinal Vowels. I found the Front Vowels easier to distinguish than the Back Vowels. If I were to pick the 8 most distinguishable monophthongs, it'd be close to the Primary Cardinal Vowels, but I'd actually replace 1 Back Vowel with a Secondary Cardinal Central Vowel. This would be it:

1 [i] close front unrounded vowel

2 [e] close-mid front unrounded vowel

3 [ɛ] open-mid front unrounded vowel

4 [a] open front unrounded vowel

5 [ɑ] open back unrounded vowel

6 [ɨ] Close central unrounded vowel

7 [ɔ] open-mid back rounded vowel

8 [u] close back rounded vowel

Is this a universal phenomenon, for people to distinguish Front Vowels more easily than Back Vowels? Is there much research on which Vowels people (whether phoneticians or from the general population) can distinguish the easiest/most accurately?

Answer 1

There is a valid trend whereby vowel height distinctions are more perceptible in front vowels than in back vowels, and if there is a front/back asymmetry in terms of number of vowel heights, front vowels will have more heights than back vowels. The pattern is clearest when you specifically look at front unrounded versus back rounded vowels, and virtually always, there are fewer heights for front rounded vowels than there are for front unrounded vowels. The most likely explanation for this that F1 and F2 are fairly well separated for front vowels, so that the exact frequency of F1 (the cue to vowel height) is more perceptible.

There is some research on the question of perceiving vowel distinctions, which involves comparing pairs of pairs – for instance, i / ɪ versus u / ʊ. A basic limit on this kind of study is that you have to use speakers of a language with the relevant contrasts, thus you can't ask a speaker of Italian to make i / ɪ judgments, since Italian doesn't have that contrast. Instead of doing perceptual experiments (which are done, anyhow), we rely more on patterns of historical sound change, for example observing a historical loss of an u / ʊ distinction while preserving the i /ɪ distinction.