I don’t think it’s easy. You have to do it by process of deduction, or perhaps experimentation. Or you get verification from others as to what they hear. Otherwise, all on your own, without seeking independent verification, you can not tell if a sound comes from the environment, or if it is something generated inside your brain.

This is a problem not just with sound, but with sights as well. It is difficult to determine what is a hallucination sometimes. The important thing is remain skeptical, and be open to the idea that your brain is making it up. It isn’t real.

It certainly isn’t infalible. I often dream of someone knocking on the door. I awaken, go downstairs, and find no one at the door.
Not even the flaming bag of dog poo I used to get.

I’ve wondered that myself and the only thing I can think of is light may act as a trigger. Your skin is sensitive to light and also, even with your eyes close they are not completely blanketed in darkness. Ever notice as the sun rises it becomes harder to stay asleep. I find even with the curtains drawn that the tiniest bit of light coming in the room through a gap acts like a lighthouse searching to get you out of the fog. At least for me it does. If I’m not in a dream state and have already had enough sleep than I realize I become more aware of my enviroment . Sounds, light, cold and hot.
When I’m really tired I have even had dreams where I am convinced I am dreaming that I got up with the alarm. In reality, I just hit the snooze till it shut off.
I think the brain doesn’t alway make a distinction. If feeds us the info we desire at the time. If we desire more sleep than so be it. If we really don’t need sleep than other things will make sure to wake us up. The desire to eat or go to the bathroom or simply to move, compels us to a lighter sleep so we can wake..
At least that is what I think from my own experience.
There is also the circadian rhythm which has to do with light and a bunch of other things that just lead us to be more aware of the fact that we are a wake.
As to how the brain can really distiguish is anyone’s guess. I’m sure if they had the answer than their wouldn’t be any people in the nut house.
The only thing I can think of is that reality has so many other things that compel us to know its real. Smell, touch, temperature, tastes, sounds and vibrations, and the last one is vision. I can often tell when something is a dream. It lacks order and often all or most of the other senses. Like when you see someone in a dream and then suddenly you are somewhere else and they disappeared. Doesn’t happen in real life situations. I think our minds are constantly trying to make sense of dalily events, except when we are sleeping.
Then we just vomit our day into our dreams and see a lot of crap that just made it to the editting floor.

I think you’ll find Julian Jaynes’ Origin of Consciousness in the Breakdown of the Bicameral Mind interesting reading. According to Jaynes’ theory, what we recognize as consciousness is only a few thousand years old, and that originally, moral decisions were made by the otherwise “unused” language centre opposite the one we use for communication today, which appears to serve no function. If this is the case, then language arose as a means of communication between the two language centres of the brain (which are connected by a very thin filament of neurons only a few thousand thick). In other words, “the gods” were actual voices which spoke to us in our own heads.

Experiments done with schizophrenics have shown that the parts of the brain connected with hearing light up when they “hear voices.” This supports Jaynes’ model, and suggests that the voices schizophrenics hear are real in the sense that they’re actually hearing them and not just imagining them.

Your question then, is really one of philosophy rather than neurology. Given that the world with which we interact is entirely representational, created by the mind as a way of creating a 1:1 scale map of the world-in-itself as understood through the perception and interpretation of qualia, it’s difficult to say whether a sound we hear, but which originates in our mind, is any less “real” than sounds which we hold to originate elsewhere.

It “knows” because externally generated sounds activate the brain’s Heschl’s gyrus, whereas imagined sounds do not. We know this from fMRI studies.

The phenomenon that you described with the alarm, where a sound is perceived as being real but the perceived source is found to be erroneous, could be caused in two different ways. It could be an auditory hallucination, where the Heschl’s gyrus is (abnormally) activated by internally generated sounds, or it could simply be that the brain took an externally generated sound of ambiguous quality and misinterpreted it. In that case, the Heschl’s gyrus would indeed be activated because the sound is indeed coming through the ear, but the source of the sound is wrongly attributed.

The brain, in vision as well as sound, often acts similarly to the word prediction function in an iPhone. It takes sketchy input and quickly tries to anticipate what that input is likely to represent. Once it has latched onto a probable interpretation, it fills in the missing bits to match that interpretation. It then can take quite a bit of counter-evidence to dissuade the brain from that interpretation.

@thorninmud
Very good reply just a few questions.

What do you mean by the Heschl’s gyrus being activated by internally generated sound?

Is the Heschl’s gyrus part of the cortex or is it more complex to say that?

Heschl’s gyrus (AKA the transverse temporal gyrus) is part of the auditory cortex, yes.

In the case of some neuropathologies, like schizophrenia, Heschl’s gyrus gets activated even in the absence of a corresponding external sound. The reason is unclear, but is often hypothesized to be a neural connectivity problem.

[mod says] This is our Question of the Day!

@augustlan
Whoop

@thorninmud
Now thinking about this topic, it’s also similar to my brain not being able to always work out when dreaming is this real or not.

@inunsure Yeah. Researchers have done some interesting studies using PET scanners, which map blood flow in the brain, on sleeping subjects. During the deep, non-dreaming phases of sleep, most brain regions gear way down. When REM sleep (the dreaming phase) kicks in, many regions get very active, some even more active than during wakefulness. An exception is the prefrontal cortex, which is usually involved in repressing unreasonable behavior. This continues to be mostly inactive during dreaming. There’s speculation that it’s the absence of the prefrontal cortex from the picture that keeps us from cluing in to the absurd nature of our dreams.