Why do we often associate “higher” sounding vowels (E, A, I) with sharp edges and “lower” sounding vowels (O, U) with round/dull/circular edges?

Question

A wiki on the topic https://en.m.wikipedia.org/wiki/Bouba/kiki_effect

In: Other

Answer 1

Make “eeee” with your mouth – you don’t have to do it out loud, it can be whispered/silent. Now, importantly, while maintaining that “eeee” position inside your mouth, *completely relax your lips.* Don’t pull them out into a smile, just completely relax them.

Notice how all the “eeee” sound requires is this one tongue position. And notice that the major characteristic of this position is that a large portion of your tongue is HIGH AND TALL, all the way at the top of your mouth, barely letting any air over it, constricting your airflow more than any other vowel. This is the skinniest and tightest your airway ever gets during the vowel parts of speaking. What’s more connotative of “skinny and tight and constricted” – sharpness and edges, or roundness and circles?

Now, also with totally relaxed lips, go “uhhh, ahhh” – your tongue is low in your mouth, and your vocal tract is as wide open and unrestricted as it can be. But you asked about O and U – good catch, as these also have some tongue height to them.

O and U do have your tongue rising somewhat to constrict the air flow. However, and you’ll notice this if you whisper “oh, oo, ee, oo, oh” to yourself, O and U are mainly the BACK of your tongue rising, leaving a bunch of space in front of your tongue for resonance (whereas “eee” has almost the whole tongue coming up and tightening away all the space in your mouth, comparatively). AND, importantly, O and U are given EXTRA space at the front of the mouth by lip rounding, which extends the vocal tract even further and provides even more space for resonance, another feature Eee doesn’t have. What’s more connotative of “space and resonance” – sharpness and edges, or roundness and circles?

Tldr: it’s about the amount of relaxed resonating space vs tight constriction left in your mouth by your tongue. Eee = very tight and constricted, which connotes sharpness and edges more. O/u = more space and resonance, which connotes roundness and circles more.

I hope that helps explain the association a little bit more 💜 source: degree in speech language pathology with undergrad study in linguistics