Dear Carol, and others trying to improve the quality of access,
Recently I have noticed the Group for Education in Museums in the UK has
published articles on access for people with learning difficulties. This
is a great addition to the literature which focuses on physical needs.
Others have broadened their understanding beyond the physical as well.
A search of the BMUSE database under the (yes, old-fashioned) term
'disabled', or 'handicapes' if you're searching in French, should give
you a broad range of the superior efforts museums are making in many
countries.
Hope this helps,
Leslie Munro.