> But I guess it's about why so we associate those with spiky shapes, though surely it's because they represent sharp immediate changes in frequency?
Sure, but it's a very abstract connection between objects being sharp in vision and frequencies changing sharply in hearing. There's no guarantee any given organism would make the connection.
In the book „the design of everyday things“ it is mentioned that „natural mappings“ exist. Moving the knob of a vertical slider to the upper end universally means „brighter“ or „louder“, not „less bright“ or „more silent“.
maybe the chicks and norman get it, but i'm currently renting an apartment in france that has a bunch of these light switches installed all upside down, with "-" at the top:
I don't think it's abstract at all. Rub something sharp (anything from a stick to a phonograph needle) on an object and you'll directly transcribe its spatial frequency spectrum into an audio frequency spectrum.
"Spatial frequency spectrum" typically refers to visual elements of an object, and has nothing particularly to do with its structure. Entirely smooth surfaces banded in different colors have a "spatial frequency". Extremely irregularly surfaces have no effective spatial frequency. Objects on the same scale as, say, a human head, would have to be "rubbed" at ridiculous high rates (and repeatedly) to even get into a "frequency" range that might include pressure variations that would be considered as a "wave".
I think you're imagining an entirely too limited set of objects.
Sure, but it's a very abstract connection between objects being sharp in vision and frequencies changing sharply in hearing. There's no guarantee any given organism would make the connection.