Reading Depends on Hearing

Everybody agrees that a key feature of dyslexia is slowness and inaccuracy in translating letters into the sounds that they represent (weak phonological skill). But this is obvious; it doesn't really explain why dyslexics have these problems. So we have been looking for more basic auditory causes of phonological difficulties.

Letter sounds are distinguished from each other mainly by changes in speech amplitude and frequency. We can understand speech because the auditory system is adapted to pick these amplitude and frequency modulations (AM & FM) up. So we have been measuring how well adult dyslexics and good readers can hear simple changes in amplitude (AM) & frequency (FM); the stimuli sound like warbles.

We found that the dyslexics were indeed significantly less sensitive at hearing the warbles. Whether you are a dyslexic or good reader, your sensitivity to these simple sounds seems to help determine how well you can develop phonological skills. Thus it seems that your basic auditory AM & FM sensitivity plays a much more important part in the development of phonological skill than used to be thought.

Several ways have been developed of training young children's auditory skills to hear these amplitude and frequency changes more easily. So we are confident that we can help children to hear phonological distinctions better and thus help them to avoid phonological reading problems later on.