I always had this view that noise cancellation demands doubling the energy in the system, to effect the cancellation. It may manifest as heat in the noise cancellation speakers, but also as pressure. In other words the eardrum system is exposed to "more" load, not less, it's just that it hears less.<p>However, the articles have been about neurological changes because of sound isolation which is different.<p>I'd be interested if the prior cohort of e.g. helicopter crew can show functional changes, deficits.