2/22/2026 at 8:10:47 AM
Objects that have sharp edges generate higher frequency harmonics when agitated, because lower-size features resonate on higher frequencies (like shorter strings ring on higher pitch). Objects that are round resonate on low frequencies only. The "kiki" sound has more high frequency content than the "bouba" sound, and it's no mystery why the brain associates one with the other.by bad_username
2/22/2026 at 2:43:24 PM
That's one theory. Another one I can think of is that sharp edges are scary, and most distress calls are high pitched.Also, the thing about high frequencies and sharp edges lead to a contradiction: babies are more round than adults and produce higher pitched sounds, this is almost universal across all species.
There are other tentative explanations, such as how the vocal tract acts when producing these sounds, with "bouba" sounds being the result of smoother movement more reminiscent of a round shape.
"kiki" is not just higher pitched, it is also "shaped" differently if you look at the sound envelope, with, as expected, sharper transitions.
So to me, the mystery is still there. Is is the kind of thing that sounds obvious, in the same way that kiki sounds obviously sharper than bouba, but is not.
by GuB-42
2/22/2026 at 6:38:00 PM
> Also, the thing about high frequencies and sharp edges lead to a contradiction: babies are more round than adults and produce higher pitched sounds, this is almost universal across all species.It's more in terms of harmonic content than the pitch fundamental. There are more harmonics from a thing with sharp transitions than there are in a thing with rounded transitions regardless of the fundamental pitch. Compare harmonic content of a pure sine wave (it's just the fundamental) with that of a square wave, which has an infinite series of higher harmonics.
Babies are also smaller, which means higher fundamental pitch.
> "kiki" is not just higher pitched, it is also "shaped" differently if you look at the sound envelope, with, as expected, sharper transitions.
Exactly!
EDIT I think this is interesting: it also applies to images as well, not just sound. You can "low pass filter" a photograph and it'll reduce some of the detail, smoothing out transitions (typically used for noise reduction). Detail is high frequency information (or high frequency noise depending on whether you want it or not.)
by scrumper
2/22/2026 at 8:08:06 PM
So you know the "bock bock" sound?Hens make it occasionally when laying eggs, but it's also the rooster alarm sound. The "cock-a-doodle-doo"/crowing sound is more the all-clear/I'm-a-rooster-here-I-am/flock-assemble cry.
When there's a threat, the rooster switches to a loud, BAWK BAWK BAWK alarm.
by saalweachter
2/22/2026 at 9:29:36 AM
In nature there's few things laying around that resonate particularly well.by IsTom
2/23/2026 at 7:59:22 PM
Maybe animal sounds count? Warning sounds tend to be loud, sharp, and high-pitched; and when ignored, they might end with more material sharp things in your skin. I can't recall any animal with a soft warning sound.by ASalazarMX
2/22/2026 at 5:39:33 PM
Hollow things are common, and of interest to many animals. If I thump a log and it makes a noise like it has a hollow space (low tones), then it may contain an animal nest or a beehive & honey, or it may be something I could use as a box or basket or shelter.by magneticnorth
2/22/2026 at 10:42:46 AM
Scratch a thin pointy branch across e rock -> sharp high noise.Thump a round club/log against a rock -> dull bump noise
by maybewhenthesun
2/22/2026 at 11:21:21 AM
Thump two round rocks together -> sharp noiseThump pointy branch against a tree -> dull noise
And chickens aren't using tools.
by IsTom
2/22/2026 at 1:59:59 PM
They're scratching for gizzard stones and food though, with their built-in beak, fwiwby blurbleblurble
2/22/2026 at 2:30:32 PM
I challenge you to find two objects of a similar size and cut them into shapes that would produce a sharper sound for the rounder object.In your example it's obviously the round tree trunk that produces the dull sound.
by sixsevenrot
2/22/2026 at 11:03:46 AM
I thought the same but they used chicks that just hatched with zero world experience.by aaptel
2/22/2026 at 1:33:14 PM
World experience can be encoded through evolution.E.g. a spider does not learn if/how to weave a web from its parents.
by amelius
2/22/2026 at 3:13:40 PM
So then the mystery would be why other primates do not appear to show the bouba-kiki effect ...by PaulDavisThe1st
2/22/2026 at 8:46:22 AM
That's what I was thinking. But then I was wondering: if it was that obvoius, would there be such research about it?by mnbs
2/22/2026 at 3:15:25 PM
Some of the research, including this paper, is trying to get at the question of whether a species' sensitivity to the bouba-kiki effect might be at the root of language or not. Since it seems accepted that chickens do not have language in any meaningful sense of that term, finding that they still show this effect decouples it from "the origins of language".by PaulDavisThe1st
2/22/2026 at 9:51:50 AM
You do need to research "obvious" things every once in a while. They have this annoying tendency of being proven wrong occasionally.by ACCount37
2/22/2026 at 11:26:38 AM
It's a hypothesis. How would you prove or disprove that it's because of that? (and I would say, a priori, it's not utterly obvious that the brain would relate spacial and temporal frequencies like this)by rcxdude
2/22/2026 at 7:39:39 PM
> The "kiki" sound has more high frequency content than the "bouba" soundAnd where did you get that from? In non-tonal languages the pitch conveys almost no information and people speak at very different ones (and for instance a male saying "kiki" will say it at lower frequencies than a woman saying "bouba" most of the time) so I find your affirmation very dubious.
> and it's no mystery why the brain associates one with the other.
Specialists of the field find that mysterious but some smartass on HN disagrees.
by littlestymaar
2/23/2026 at 6:07:01 PM
> > The "kiki" sound has more high frequency content than the "bouba" sound> And where did you get that from? In non-tonal languages the pitch conveys almost no information and people speak at very different ones (and for instance a male saying "kiki" will say it at lower frequencies than a woman saying "bouba" most of the time) so I find your affirmation very dubious.
You misunderstand the post. It has nothing to do with the voice of the speaker.
Long drawn-out sounds have lower frequency components than short-lasting sounds. A pin drop is REALLY high-pitched; a moan has at least some low-pitch components (but may still be high-pitched, too - more often called a "keening" than a moan). It's not about intonation; it's a mathematical consequence of the relationship between frequency and time-domain incidents, typically measured with Fourier transforms.
by IAmBroom