Dictionaries, encyclopedias, and handbooks are good places to begin your research. They can give you an overview of the topic and explain the basics, like symptoms, diagnosis, typical treatment, and so on. Some reference sources can also provide short reading lists, history of research on the topic, and the current state of knowledge.
Gale Virtual Reference and Oxford Reference Online: Premium Edition have several online reference resources, including several dictionaries of medicine.
These links take you to the online catalog::
Dictionaries for Communication Disorders
Encyclopedias for Communication Disorders
Handbooks for Communication Disorders