posted on Nov, 18 2009 @ 04:21 PM
I'm not sure of any studies I could cite off-hand, and I don't have the time just now to check it out. So this is mostly just a tag post till I get
back in a few hours.
(I don't have time to do my basic fact checking, so consider the following as speculation for now)
Your auditory cortex has the ability to recognize and process the volume of noises you hear around you. That's how you can tell what direction a
noise is coming from - basically by contrasting the difference in volume levels between the left and right ear. The one furthest from the source will
register slightly lower.. even if you don't consciously notice it at times.
The Audio and Visual cortex regions in your brain are extremely similar in functionality when they are first formed, and are specialized later in
devlopment. Tests in ferret embryos to knock out the visual cortex and re-route optic sensory information to the auditory cortex show that it's
possible for the auditory cortex to actually process both visual and audio stimuli simultaneously if prompted to early enough - but with reduced
functionality of either sense.
I also know that fMRI scans of brain activity shows that when patients are prompted to visualise in their mind a shape, face, etc - their visual
cortex lights up with activity. So your visual cortex doesn't just process sensory imput from your eyes, but also processes the data for your
"mind's eye". Off-hand, considering all that above, I see really no reason why it'd be fundamentally different for imagined audio properties. I
feel confident suggesting that differentiating between loud and soft internal voice is no more strange or obscure... and probably a very similar
process... to differentiating between a green mental image and an orange mental image.
Edit: Doing some basic research. Thought I'd post some links to earlier statements.
--Journal Nature - Musical imagery: Sound of silence activates auditory
I'm not sure as to the exact mechanism which turns up the volume on the subvocalization, and the abstract doesn't mention that aspect. It may be in
the full paper, but you have to pay for the article. At least it confirms my supposition that mental dictation stimulates the auditory cortex. Again,
if I had to speculate - I'd suggest that "mental volume" (being subjective) is more an effect of quieting noise/interference from other processes
and thoughts in the executive consciousness. For instance, if you stand next to an explosive charge - the blast will register at extremely high
decibels which seem to be hard to emulate mentally.
(Though the assembly of ideas into a complete thought and the correlation between words and meaning occurs elsewhere.)
Here's a few other links to some research abstracts which are related that you might find interesting.
inflences on ferret auditory cortex.
PubMed: Visual speech perception (sign language) without primary auditory cortex
PubMed: Primary auditory cortex activation by visual speech.
Crossmodal audio-visual interactions in the primary visual cortex of the visually deprived
cat: a physiological and anatomical study.
PubMed: Rapid and reversible recruitment of early visual cortex for touch.
[edit on 18-11-2009 by Lasheic]