Dr. mattar wants to learn about the effects of brain injury to the occipital cortex, so he observes a few patients to gain in-depth knowledge about their behaviors. which type of research method is dr. mattar using?

That would be an example of a case study.

Case studies are in-depth, highly specialized and detailed examinations of a certain problem. This is a really up close research method that studies, examines the case that is the subject of examination. Case studies are the usual thing to do in this situation and they are of immense value to their field but are not generally represented in more popular works mainly because they require a high knowledge of the field and the problem within a particular field. 

Ok we will i'm sure 456