John Marshall mostly deals with Cognitive psychology, Neglect, Cognition, Visual perception and Neuropsychology. His Cognitive psychology study combines topics from a wide range of disciplines, such as Dyslexia and Surface dyslexia. His biological study spans a wide range of topics, including Developmental psychology, Learning to read and Acquired dyslexia.

The study incorporates disciplines such as Space, Neuroscience and Audiology in addition to Neglect. His Visual perception study integrates concerns from other disciplines, such as Lateral dominance, Inferior parietal lobule and Set. He has included themes like Spatial ability, Mental representation, Spatial cognition, Reading and Representational systems in his Neuropsychology study.