Sound could be even more subjective than we thought

[tikker]

Disclaimer: I'm an astrophysicist, not a neuroscientist. All the non-quotes are my interpretation of the article.

 

Sources:

https://elifesciences.org/articles/64501 - this is the scientific article
https://www.eurekalert.org/pub_releases/2021-01/tud-whw010821.php

 

Not completely tech, but I thought it was interesting nontheless after my recent dive in audio equipment. It is already hypothesized, and to certain extents known, that our brain does a lot of inter and extrapolation when it comes to our senses. We can't process all the information we receive in real time, so we make certain assumptions about how the world around us looks, for example, and how it will look in a moment. The general idea behind it is that we respond to differences rather than constantly actually processing what we perceive. Think of the gorilla walking through the basketball court. The other day I found an article that explores this in the context of audio.

 

Article breakdown:

Spoiler

Abstract rules drive adaptation in the subcortical sensory pathway

Abstract

Quote

...

These results provide first unambiguous evidence of abstract processing in a subcortical sensory pathway. They indicate that the neural representation of the outside world is altered by our prior beliefs even at initial points of the processing hierarchy.

The experiment

Quote

Nineteen subjects listened to sequences of eight pure tones (seven repetitions of a standard and one deviant tone; see Figure 1A–B). Tones were taken from a pool of three tones and used equally often as standards and as deviants. Subjects reported the position of the deviant for each sequence by pressing one button of a response box as quickly as possible.

...

If coding at the subcortical pathway was based on expectations on the incoming stimuli, that would mean that the brain does not hold a veridical representation of the environment even at the very early points of the processing hierarchy.

 

Expectations for each of the deviant positions were manipulated by two abstract rules that were disclosed to the subjects: (1) all sequences have a deviant, and (2) the deviant is always located in positions 4, 5, or 6. Note that, although the three deviant positions were equally likely at the beginning of the sequence, due to the two abstract rules the probability of finding a deviant in position 4 after hearing three standards is 1/3, the probability of finding a deviant in position 5 after hearing four standards is 1/2, and the probability of finding a deviant in position 6 after hearing five standards is 1. This means that participants expected deviants at all positions, but with different expectations of the probability of finding the deviant. Therefore, habituation and predictive coding make opposing predictions for the responses at the different deviant positions (Figure 1B). According to the habituation hypothesis (Figure 1C, left), deviants will elicit roughly similar responses independently of their position. Conversely, under the predictive coding view the response is hypothesised to scale with the probability of finding a deviant in the target position (Figure 1C, right), rendering responses to earlier deviants stronger in contrast to the later deviants.

Participants were asked to identify the odd one out of a series of sounds and were given expectations on where the outlier sound would be. The goal was to see if there was evidence preferring one of two theories regarding auditory stimuli, which I emphasized in the quote. The first one states if we expect something, we respond less to it. The second one states that the amount by which we react less to it depends on how well we can predict our expectation.

 

The central question here is whether our brain has an idea of the underlying truth, responding based on that, or whether we respond because something differs from what we think is the truth.

Quote

Deviant detection can be abolished by making the deviant predictable

The correlation analyses suggested that the mesoscopic responses in the IC and MGB to the deviants can be interpreted as prediction error.

...

The negligible differences between the responses to the fully expected deviant (dev6) and the standards after the deviant (std2) fits the predictive coding framework perfectly: although the deviant is different from the standards in terms of frequency, it elicits the same response as a standard. Thus, deviance detection can be virtually abolished at the mesoscopic level by manipulating subjects’ expectations; that is, by rendering the deviant predictable.

They pose their data suggests our brain predicts where in the sequence it will hear the outlier sound and that the way we respond to it is determined by if what we hear matches our prediction. As described in the setup above, the outlier sound will occur at most after five of the normal sounds. That means we 100% expect to hear the outlier after hearing the normal sound five times. We also 100% expect the seventh sound to be normal, as the outlier can only happen at 4, 5 or 6. Their result shows our brain responds the same to the expected outlier as it did to the normal sound.

Quote

Conclusion

Together, the findings indicate that sensory processing in auditory midbrain and thalamus are mostly driven by expectations of the subject and not by regularities in the local stimulus statistics.

They finish off with the conclusion that low level brain components already change our perception of the world. Our brain doesn't store the truth (i.e. the underlying pattern of normal sounds) reacting equally to deviations from that (the outlier sounds), but creates its own truth (a prediction) based on what it is told to expect and responds more strongly the more the observation deviates from what it predicted.

 

TL;DR Our brain seemingly doesn't store the (full) truth, but makes a prediction* and reacts based on how much the observed world deviates from what we expect very early on in our "signal processing chain".

[Edit] *important point that I forgot to add here: this prediction changes depending on the rules we are told the truth abides by.

 

Why am I posting this here? I think it's an interesting discovery. This study does not imply that we hear what we want to hear, but rather that we use what we think of as the truth as a reference for experiences. I think it would be interesting (if that were somehow possible) to see if this also correlates with excitement/disappointment in upgrades due to reviews, for example. What we read or are told our new gear will do, will change our truth and thus how we experience that new piece of gear when we use it for the first time. The more it deviates, the stronger our brains respond and so potentially the more/less excited/disappointed we are!

 

Finally I think it shows the value of blind testing as that makes it much harder to form a personalized truth.

 

Any thoughts from other people? Have you ever tried a blind test of your equipment and maybe found differences between them or a different ranking you didn't expect to find at first?

 

[Radium_Angel]

5 minutes ago, tikker said:

Our brain seemingly doesn't store the (full) truth, but makes a prediction and reacts based on how much the observed world deviates from what we expect.

Why yes, thank you, I will take that 10k$ in audio hardware you are offering, that is very kind of you!

[tikker]

5 minutes ago, Radium_Angel said:

Why yes, thank you, I will take that 10k$ in audio hardware you are offering, that is very kind of you!

 Free of charge! If I expect hard enough, my Logitech set will beat any system out there. If only I had 10k in (good) audio equipment haha.

 

I didn't mean to frame this as an "you're all fools with your $5k a speaker setups" btw, just to make that extra clear I still believe that higher end stuff gets better (with diminishing returns down the line of course) and that there are objective differences in terms of how things sound. Just thought it was interesting that our expectations on how we will experience that sound could in itself be an important factor in how we experience that sound.

[Radium_Angel]

2 minutes ago, tikker said:

I still believe that higher end stuff gets better

 

 

[The Flying Sloth]

This isn't a new concept by any means, it seems these researchers have found a way to repackage the placebo effect with far longer words, I'd imagine they're quite proud of themselves for that one.

[tikker]

1 hour ago, The Flying Sloth said:

This isn't a new concept by any means, it seems these researchers have found a way to repackage the placebo effect with far longer words, I'd imagine they're quite proud of themselves for that one.

True, we've know for a long time that the placebo effect exists and that the brain assumes a lot of things on autopilot, correct or not. They start off the article saying that it is known expectations influence results. In the case of placebo, what we don't fully understand why it works. In this article the point wasn't to confirm the placebo effect or to introduce the concept, but to search for evidence for or against either of two competing ideas about how exactly expectations change our response.

 

This is more presenting findings/evidence that the theory in which we constantly adjust our brain based on what we observe and the rules we are given, which then becomes the new "truth" happens down to a lower level than thought. So it's even more innate to us that we don't hear / experience "the true world" than previous studies have shown.

 

In the end it's another step of understanding our brain better, which I find fascinating.

[The Flying Sloth]

1 hour ago, tikker said:

True, we've know for a long time that the placebo effect exists and that the brain assumes a lot of things on autopilot, correct or not. They start off the article saying that it is known expectations influence results. In the case of placebo, what we don't fully understand why it works. In this article the point wasn't to confirm the placebo effect or to introduce the concept, but to search for evidence for or against either of two competing ideas about how exactly expectations change our response.

 

This is more presenting findings/evidence that the theory in which we constantly adjust our brain based on what we observe and the rules we are given, which then becomes the new "truth" happens down to a lower level than thought. So it's even more innate to us that we don't hear / experience "the true world" than previous studies have shown.

 

In the end it's another step of understanding our brain better, which I find fascinating.

While this is no doubt interesting to read about, as someone with a psychology qualification this is all general/common knowledge to the point where you might spend an hour on the subject maximum over a full degree. 

[tikker]

1 hour ago, The Flying Sloth said:

While this is no doubt interesting to read about, as someone with a psychology qualification this is all general/common knowledge to the point where you might spend an hour on the subject maximum over a full degree. 

Ah that's good to know. I'm happy to take your word for that. Always hard to judge to which extent things are already common knowledge within a field as an outsider.