As Gary Chevin watched his wife Carol reading a newspaper, he had a sudden realisation.
Diagnosed as severely dyslexic at seven, he had always struggled to read.
Gary noticed that Carol was reading without moving her lips, which seemed odd to him as a dyslexic. 'She told me she was reading in her head,' says Gary. 'I asked what that sounded like and she said it was like a voice.
Mind set: Gary Chevin is learning to develop his own inner voice when he reads
'I have never heard a voice in my head - ever. I was so shocked I nearly fell off my chair.'
Gary, 50, was stunned to learn that when 55-year-old Carol read a letter, she would hear the writer's voice, rather than her own, in her head - and that in her dreams, people spoke.
'It all seemed so alien to me. I have the reading age of a five-year-old so I never read. If I dream, I have visual dreams. They are always totally silent.'
Most people use their inner voice subconsciously. But for those who find they do not have one, it can be a revelation.
'I now understand my actions a lot more,' says Gary, a former builder from Stoke-on-Trent. 'I follow my emotions because I don't have a voice in my head analysing what I'm about to say or do.'
Professor Rod Nicolson, head of work psychology at the University of Sheffield, has been studying dyslexia for many years and was inspired to investigate internal speech after meeting Gary at a conference in 2004. He believes he has found a link between lack of inner speech and poor reading ability.
'Children start off having to say every word out loud,' he says. 'At some stage, as their reading improves, so does their ability to sight-read [to read in their heads] and that is the stage at which reading really takes off.
By the age of eight or nine, most children can read in their heads. The development of the inner voice seems to be automatic for most people, but our data suggests a link with fluent reading, in that the process of learning to sight-read actually helps inner-speech develop.
TEST YOUR INNER SPEECH
'Everyone assumes everyone else is the same. However, we have found not everyone has an inner voice and in those who don't, literacy levels are often poor.
'But we have also found a lot of children with dyslexia who have well-developed inner speech.' Prof Nicolson believes that like ordinary speech, there are different degrees of fluency of inner speech. 'It's probably "use it or lose it",' he says.
Dr Kate Saunders, of the British Dyslexia Association, says the idea that some dyslexics have no inner voice is new. 'It is possible there may be a link with dyslexia for some individuals, but we shouldn't make any sweeping statements,' she adds.
No one knows for sure what causes dyslexia but 'at risk' signs can be detected in children as young as three. There is evidence from brain-scan research that when dyslexic individuals read, key areas on the left side of the brain important for the processing of language are not as activated as they should be.
Consequently, those with dyslexia struggle with reading, spelling and writing and can have difficulty making the link between the written word and the phonetic sounds in words. Early diagnosis and well-structured, multi-sensory phonics-based teaching programmes can help.
Dr Saunders says 30 to 50 per cent of those with dyslexia also have Attention Deficit Hyperactivity Disorder, a medical condition affecting how well someone can sit still and focus. It is believed that many of those with ADHD may also lack an inner voice.
Prof Nicolson is seeking volunteers who suspect they have little or no inner speech to undergo Functional Magnetic Resonance Imaging (fMRI), a non-invasive brain scan using a powerful magnetic field, radio-frequency pulses and a computer to measure tiny metabolic changes in the brain.
It should detect when someone is using internal speech.
'So far our research has been based on simple tests we've devised ourselves,' he says. 'Using an FMRI scanner will provide a strong test for our theory.'
For Gary, there is still hope. He has software that turns his speech into type on his computer, and vice versa.
Listening to emails via his earpiece has helped him develop an inner voice, although he has to concentrate to hear it.
'I feel so sad when I think of what I went through at school,' says Gary, whose two grown-up children also have dyslexia and no internal speech.
'I hated every single day. Many schoolchildren are still struggling and more research is needed to help them.'
If you would like to take part in the research, contact Prof Nicolson at www.dyslexia visualldeafauditoryblind.com.
The Government is releasing £10million over two years to fund various dyslexia projects. Teachers in England wishing to apply for a place on a Dyslexia-SpLD course visit www. thedyslexia-spldtrust.org.uk.