Why spiky shapes seem angry and round sounds are calming

Thanks for the comment. Thoughts not dissimilar from yours are what drove us to undertake these studies. :)

I definitely suspect that predictive processing in the brain is part of the story, and we discuss that a bit in the paper. Interestingly, local entropy is highly correlated with our "spikiness" measure, the spectral centroid. However, where your comment focuses on macro-level regularity, like Bach versus Rush, our study focused on micro-level texture, like the hum of a box fan versus squealing brake pads. Although macro-level regularity definitely has an impact on emotion perception as well! This is something my other research has touched on, e.g.: https://www.pnas.org/content/110/1/70

We also found that "spikiness" predicted emotional arousal for both positive and negative emotions. E.g., "angry" and "excited" are both spiky across the senses, while "sad" and "peaceful" are both smooth. So the results can't be driven solely by uncertainty becoming associated with negative emotion.

Thanks for your thoughts! And here's a link to a preprint of the paper: https://psyarxiv.com/wucs4

This is a great observation, and lines up well with something I've been thinking about recently. Some HN posters may be familiar with ASMR; if not, https://en.wikipedia.org/wiki/Autonomous_sensory_meridian_re... is a reasonable jumping off point. I'll assume basic familiarity with the idea of "triggers" - primarily auditory, these are actions / sounds that cause the tingly ASMR effect. Some triggers seem to work on really large groups of people (e.g. mouth sounds, repeated words).

From an audio standpoint, triggers often seem to be highly correlated with audio transients ( https://en.wikipedia.org/wiki/Transient_(acoustics) ) - quick little sounds with a lot of detail. From an information-science standpoint, transient sounds convey more information in a short time period than does, say, a uniform sine wave, or music, or even talking.

There's a lot happening there, and it's not very predictable; but at the same time, the entire setting of the content is generally predicated upon relaxation. It's possible that the triggering sounds are stimulating that kind of negative / fight-or-flight / sudden-action-required sort of interrupt you're describing. The difference is that because of the context, the listener can immediately return back to feeling safe and comfortable again after the transient is past.

I have personally noticed that the most triggering kind of content for myself is content where I can _almost_ predict what's going to happen, but when it surprises me slightly. Repeated trigger words work really well for this - by the 3rd repetition my brain has an excellent profile of how the ASMR practitioner is going to pronounce a word, but there are always slight differences, unexpected timing, etc. that go into it. I'm not yet sure whether the trigger happens more on a prediction hit or miss; leaning towards a hit at this point.