RadioLab has a fantastic mini-edition about the link between our internal thought stream and the development of auditory hallucinations – the experience of ‘hearing voices’.
The programme discusses the theory that the experience of hearing hallucinated ‘voices in your head’ occurs when we lose the ability to recognise our internal thoughts as our own.
Although there is some good evidence that, for example, people diagnosed with schizophrenia who hear voices are less able to recognise their own actions as their own, one crucial aspect not explained by the theory is why many ‘voice hearers’ experience voices with distinct identities.
For example, someone might hear the voice of their dead parent along with someone they knew from childhood where someone else might have discovered the identities of their voices over time, simply from hearing them speak, and they seem to have no relation to specific people they’ve met in their lives.
The programme suggests the idea, which, as far as I know, has never been discussed in the scientific literature, that the identities of the voices could originate from when we learn to internalise voices of people who give us instructions when we’re children – an approach based on the theories of Lev Vygotsky.
It’s a delightful idea, if not a little blue sky, and is accompanied by a brilliant demonstration of the type of study that focuses on hallucinated voices.
UPDATE: There’s further discussion with references to Vygotsky’s work on self-talk and internalised thought from the interviewee, psychologist Charles Ferynhough, over at a great post on his blog.
Link to RadioLab ‘Voices in Your Head’ edition.
Mind Hacks 
Does this give any support to Julian Jaynes idea that the early Greek gods were nothing more than auditory command hallucinations?
I thought of Jaynes too. He posited that the hallucinated god voices were ‘overheard’ in the brain through some cross wiring between the hemispheres.
@Russell;
What intrigued me was the suggestion that the command voices were internalized as children.
The internal voice is also linked to silent reading, both developmentally, at the age mentioned by Vygotsky, but also historically. The whole idea of an ‘inner space’ does not occur in literature prior to the decline of oral reading practices. Hence, our sense of a psychological interior, where we hear our own voice, is fundamentally linked to our reading practices
Full article (award-winning, if I do say so myself!) here: http://www.ncbi.nlm.nih.gov/pubmed/18196548
Pre-publication copy here
Click to access Origins_of_the_psychological_’interior’_-_evidence_from_Imperial_Roman_literary_practices.pdf
Any speed reader knows you can think perfectly fine without subvocalization.
Game over.
I think is worthy to classify distinguishing both kinds of thoughts.
But telling people that they can’t think outside words is misleading (being generous).
Inspiration, sudden perceptions, sudden realization of patterns, etc.
This isn’t controversial at all.
@Ciarán well pointed