Recent work out of Linkoping, Sweden suggests that new hearing aid wearers experience greater cognitive demands when listening. Over time they adapt to better resolve new auditory cues, decreasing the effort required for listening.
Ng, E., Classon, E., Larsby, B., Arlinger, S., Lunner, T., Rudner, M., Ronnberg, J. (2014). Dynamic relation between working memory capacity and speech recognition in noise during the first six months of hearing aid use. Trends in Hearing 18, 1-10.