Thank you for your answer. I mean that deaf or hard of hearing people have problems in syntax, figurative/ metaphor language, communication problems, problems in emotion recognition and lack of empathy? Are there some surveys to prove these problems in deaf or hard of hearing people?
For empathy, you could look at what these people did: Empathy Development in Deaf Preadolescents.
I don't know about the validity of their results, but they state: "The results demonstrate that deaf preadolescents have more difficulty with empathy development than hearing children, and this ability is related to onset of deafness."
Please, pay attention on the fact that this research is from 1980. I would take with caution because we can label people so easily - but so wrong. If I can remind you, those years were present some great deceptions in the main pediatric`s book like "simian crease" which is outdated and not politically correct.
So, I believe that we should take this statement with skepticism.
On the other side, I would rather add the possibility that deaf and hard of hearing people because of their hearing loss do not expose easily their affections but this does not mean they do not have them.