This is particularly interesting for us as it applies to the masking effect lossy audio compression takes advantage of.

http://biology.plosjournals.org/perlserv/?...060138&ct=1

Author summary:
Sounds that are well above the sensory threshold may sometimes
fail to be perceived when they occur amid competing sounds, as
often happens in everyday life. This phenomenon is generally
referred to as ‘‘informational masking.’’ We took advantage of this
effect to isolate brain responses that correlate with conscious
auditory perception. Human listeners performed an auditory
detection task in which they had to indicate when they heard a
stream of repeating tones (targets) embedded in a stochastic tone
background (masker). At the same time, brain responses were
recorded using magnetoencephalography. By comparing the
responses to perceptually detected and undetected target tones
in the auditory cortex, we isolated a neural response component in
the latency range of 50–250 ms, which was only present for
detected sounds. We propose that this component, the ‘‘awareness
related negativity,’’ specifically reflects conscious sound perception.
In contrast, earlier responses in the auditory cortex were evoked by
both detected and undetected target tones. These results suggest
that conscious sound perception emerges from within the auditory
cortex.

It's a fascinating paper, suggesting that masked sounds don't ever make it out of the auditory cortex (not that this is anywhere near a field I know about). Deeper understanding of the way the brain interprets stimuli is a good thing - the understanding of the brain has been a big area for pseudoscientific BS for a long time.

Oh, and open access publishing is awesome. I wish there was something like PLOS in my field.

So the ear (auditory cortex) is able to isolate sounds even in the presence of a masking sound, but further down the line the signal is interpreted in such way that masked sounds are discarded?

Does the auditory cortex have any function other than audition? Can we say that the presence or absence of the masked signal in the audio has no effect whatsoever on our perceptions and/or brain mechanisms?

I'm not an expert in this subject, but yes, that is essentially what I got out of it. They found equal low-mid latency responses in the brain for both target sounds and masked sounds. However only the target sounds produced a high-latency response in the brain, suggesting that somewhere along in the processing of the signals in the brain, the masked sounds are discarded.

I'm a lame person when it comes to this, but I had always imagined it was possible the masking effect was somehow due to the shape of the human ear or some physical phenomenon that canceled out the target sound. This paper shows that is incorrect.



Those are great questions. Presumably, because there was no high-latency response in the brain to the masking sound, in the end, they are not "heard" by any other part of the brain, conscience or unconscience.

To be fair, there is just as much BS in mental science, as there is in "mental pseudoscience" - they both just make different errors.

For example, what i completely miss in that paper, is taking cultural effects (poisoned sample pool) into account, as well as checking if consciousness may modify the described behaviour BEFORE the stimuli is triggered. I'm not saying that the paper useless - it is interesting - but its also incomplete and suffers from motivation-bias.

- Lyx

P.S.:

Unless you want to break causality, there will always be consequences. A wave doesn't stop suddenly in the middle of the pool.... but it gets smaller and smaller. The question here isn't if there is an effect, but if it is *significant*. If an effect isn't significant enough, it gets ignored one way or the other.... since else, mentality would drown in chaotic noise.

From reading the paper's first paragraph under the heading Introduction, it appears that there are two types of masking, so I'm not sure your first paragraph is correct. For one thing, I think the ear is the ear, but the auditory cortex is in the brain at the other end of the auditory nerve, and actually beyond the auditory brainstem and regions in the midbrain. (see http://en.wikipedia.org/wiki/Auditory_cortex)

First, there's "energetic masking" that is well understood in psychoacoustics, much of which can be understood from the biomechanics of the ear. Here the masking signal swamps the nerve response such that a smaller signal is not represented properly in the auditory nerve, so in the absence of nerve response related to that signal, it will presumably be unable to reach any part of the auditory cortex of the brain to have any chance of being perceived. The other example is probably ATH.

The topic of interest in this paper is "informational masking" where the signal probably does create a nerve response and reach the early stages of the auditory cortex but there are so many competing signals that also reach the auditory cortex that the signal is ignored in favour of other signals that the brain may have evolved to deem more likely to be important.

At least that's my initial interpretation.

I don't know whether any of this informational masking is exploited in lossy audio. I'd expect tonal and noise masking is "energetic masking". I'd imagine "temporal masking" is also energetic. Perhaps the ability to degrade stereo information transparently at times might be an informational masking effect that occurs in the auditory cortex, though I know nothing about it, so don't rely on my supposition.