Friday, March 23, 2012

Why We Hear What We Hear, Part 4 (end)

What This Means about What You Hear

The plasticity of forming auditory features and auditory objects has some very strong implications. If you listen for different things, you will hear different things. This is not illusion, it is not confusion, it is not deception, it is not hallucination, it is simply how your brain works. This has a particularly important implication for audio enthusiasts, which is expectation will always cause you to hear things differently. The effect of expectation is not always positive, or negative, for example you may not hear what you expect to hear, but expectation can not, not now, not ever, be consciously filtered out of your hearing experience.

Expectation is why audio testing needs to be what’s called “double blind”. Double blind does not mean that you close your eyes, wear a blindfold, or have anything to do with vision. Blind means that when you are trying to identify something you do not know which of several (usually two) signals it is, even though you can, or should be able to, switch to each of the known signals at will for reference and comparison. Double means that any experimenter you interact with in any fashion also doesn’t know which you’re hearing. Lots of work has shown that cues from an experimenter will lead you to answer differently. Interestingly, you may not agree with the experimenter in a single-blind test, you may take the other answer than the one the experimenter prefers, but your performance will be affected.

This can be demonstrated by the old “backward masking” demonstration that was originally brought up in a different context, where it was alleged that there was satanistic content to part of the song “Stairway to Heaven” when it was played in reverse. Interestingly enough, when the reversed song is played to an unsuspecting audience (this has happened quite a few times in lectures), the audience hears nothing, or a very few random syllables. When, however, the “words” are presented, the audience hears the words clearly and correctly, even though the actual sound presented to the ear is not changed. This is a direct result of how we understand speech, when expecting speech with some particular content, we guide our feature extraction and object resolution to find the parts of our audio surroundings in order to extract the information, and in this case can do so even when there is no such information. This kind of effect is echoed in “EVP” arguments, wherein sounds, whispers, etc., are supposedly heard in recordings of radio static or other random noise.

In summary, the processing done in the brain is exceptionally plastic, and can be guided by a variety of things. The result of all that processing is what we actually, consciously hear.

  • If you listen to something differently (for different features or objects)
    • You will remember different things
    • This is not an illusion
  • If you have reason to assume things may be different
    • You will most likely listen differently
    • Therefore, you will remember different things

In short, if you want to be sure of what you heard due to only the auditory stimuli, you need to arrange a blind test of an appropriate nature. Such tests are neither easy nor simple to arrange, but are the best, and perhaps only way to avoid inadvertent self-deception.

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