>But I guess it's about why so we associate those with spiky shapes

I think the why just got a lot tricker than we imagined. Because we failed to replicate this experiment on other primates, we couldn't avoid a semantic suspicion about those associations. Now we probably have to set semantics aside or let it get a lot weirder, because we can replicate across ~300My.

>surely it's because they represent sharp immediate changes in frequency?

Maybe, and I think "multi-sensory signal processing" is the best framing, but the representation could also carry harder to think about things like "harm".

It's also super cool because the bouba-kiki effect framing was chosen due to methodological convenience for linguists and cultural anthropologists and their experimental bounds, not neuroscientists or signal processing folks. We could potentially find other experiments quickly, since chicks are a model organism and the mechanism is clear.

Things could move fast here.