A Welsh psychiatrist has claimed that some iPod users are experiencing what he calls "musical hallucinations".
Dr Victor Aziz said that the effect can occur when people spend many hours listening to the same songs. The hallucinations are characterised by a song " playing" constantly in the head, according to the psychiatrist, and the effect has caused sleeping problems for some of his patients.
"People find they can't sleep and can't think properly," he told the Evening Standard. "Having a song in your head every now and then is quite normal, but musical hallucinations can be quite distressing."