Auditory Scene Analysis. a quick overview | by Myk Eff | Dec, 2021


a quick overview

Gestalt Parallels

gestalt principles (image source)

Auditory Scene Analysis (hereafter ASA) probes questions around how we are able to perceive unique sonic events and sources, when our acoustic environment is full of simultaneous overlapping sounds.

To draw a visual contrast, if you layer many images on top of each other, say by applying some transparency amount to each them, they will add up to a kind of visual mush and eventually lead to black or at least a very unappealing dark brown. Try this in Photoshop or whatever image editor you can access — load in many images on top of each other as layers, and give each one a 50% opacity — the result will not be pretty.

With images, we usually like to see one single image at a time happening. But there is a notable exceptions worth discussing briefly. You might think that collage might be an exception, since they present pieces of images in juxtaposition. I would argue, though, that a collage is still just a single image, and is not categorically different from any other image since all images can be said to be a whole made up of multiple parts.

The main exception with visual media (that I can think of presently) is with double exposure effects, where careful layering of usually just two images allow us to see two of them simultaneously.

Double exposures in the image domain — two co-occurring images (image source)
Double exposures in the image domain — two co-occurring images (image source)

But note the name of the effect — double exposure. As in, just two images. If you google ‘triple exposure’ images, you instead get examples of ‘multiple exposure images’ that are mostly actually just double exposure images.

With sound, in contrast to images, it’s common practice and completely normal to accumulate layer upon layer of co-occurring sounds. Unlike with images, this doesn’t lead to the kind of confusion in object/event/source information that we might get with this kind of approach to multiple-exposure photography:

Multiple (more than two) exposure in photography. image source

If your dog is barking while the tv is playing and the stove alarm is beeping, each of those is a unique auditory stream happening in your immediate auditory scene. The most well-known everyday concept from ASA is the ‘cocktail party effect.’

The cocktail party effect or phenomenon in psychology is our ability to tune into a single voice from many conversations going on in a noisy room. For psychologists the ‘cocktail party effect’ or phenomenon is our impressive and under-appreciated ability to tune our attention to just one voice from a multitude. At a party, when bored with our current conversational partner — and for the compulsive eavesdropper — allowing the aural attention to wander around the room is a handy trick. (source)

The mind’s ability to form streams of separate sonic events and sources happens at a cognitive level — systemically ordered ‘higher’ or ‘above’ psychophysical or psychoacoustic phenomena. At the cochlear level, for example, all unique sounds are a ‘general mush’ of non-individuated sounds, similar to the multiple exposure black and white photo above. Stream segregation is neuro-cognitive (post-Cochlea) and thus part of the Central Nervous System.



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