It has been mentioned on quite a few occasions.
Parents or caregivers initially suspect that their young child presents with a hearing problem when, for example, the child seems non-responsive to their name being called or when their attention is sought (see item 14 of the M-CHAT). The child submits to a hearing test and some of the time, nothing untoward is found. The question is then asked: could it be autism?
Likewise, there have been occasions when parents have initially suspected autism and, following a hearing test, it has transpired that the child has hearing problems. You can see that there is some overlap here.
Like visual impairment, hearing impairment (deafness, hard-of-hearing, if you wish) moves across quite a bit of ground; ranging from the source of the problem, through to the extent of the loss. Also like sight, many people would describe hearing as probably being one of the more primary senses in terms of its importance to daily life - language and communication, social interaction, balance, etc (some of these sound familiar?).
Hearing is so important a sense that, certainly here in the UK, the day of (or day after) birth, newborns have a hearing screen complimentary of the NHS Newborn Hearing Screening Programme. From what I am aware, there is no equivalent programme offered for sight throughout infancy; allowing though, for the difficulties of objective vision testing in newborns.
Looking at the rates of hearing loss in autism and in the general population, the RNID estimate that 1 in 1,000 children (0.1%) in the UK are deaf at age 3. The figures for other age-groups are slightly more complicated but between the ages of 16-60 years, the estimated prevalence of all types of deafness is 6.6%.
In autism, the estimated occurrence of co-morbid hearing loss (all types) is round about 10% in children and adolescents (note that this is a study published in 1999 carried out in Sweden). Obviously the age ranges don't exactly match up with the RNID figures, but the general suggestion is that hearing loss may be more prevalent in autism compared with the general population figures.
Issues with hearing in autism are not solely confined to a loss of function. Some people with autism (and their parents / caregivers) report issues with the perception of hearing; that is things like hyperacusis. There is some good evidence to suggest that the perception of loudness might be perturbed in some cases of autism. Indeed, for some children, the option of ear defenders / ear plugs is a vital course of action to block out what can often be quite disturbing sensory input.
What causes such hyperacuity? I don't think anyone has an answer for that yet. There is some suggestion that it might be down to sensory gating or temporal processing in specific groups on the autism spectrum but much more research is required. Readers may remember my recent entry on vision and autism; perhaps there is some shared mechanism with the perceptual issues highlighted in that area too - whereby our senses are linked together?
What can be done about hyperacusis? Again, there are no universally 'right' answers to this. My first thought would be that adapting the environment to the child/person with autism should be key. It is however probably impossible to remove all sound altogether - also impractical for a person who might have to go to school, go outside, etc.
Like the various comments on vision processing in autism, one course of action proposed is to think about ambient noise and its potential effect. The humming of the lights; certain pitches in people's voices; singing; dogs barking etc - these are all things which have been suggested by people with autism to be a source of often, real irritation (obviously there are a lot of other things too).
I previously mentioned ear defenders as one option, and indeed this young lady found them to be useful for her (also her iPod - no advertisement intended). Various other options have also been suggested, including things like auditory integration therapy (AIT) - although make sure that you do your research first. One final point of information and help may also come from a referral for the child to their local audiologist.
Most guidelines for autism screening and diagnosis do include some reference to hearing assessment. Hopefully also this will be included in the upcoming NICE guidelines on autism, and indeed research also expanded on the important issue of how hearing and autism are connected.