Neuropsychology involves the study of both healthy individuals and patients, typically who have suffered either brain injury or mental illness.
Cognitive neuropsychology and cognitive neuropsychiatry study neurological or mental impairment in an attempt to infer theories of normal mind and brain function. This typically involves looking for differences in patterns of remaining ability (known as 'functional disassociation's') which can give clues as to whether abilities are comprised of smaller functions, or are controlled by a single cognitive mechanism.
In addition, experimental techniques are often used which also apply to studying the neuropsychology of healthy individuals. These include behavioral experiments, brain-scanning or functional neuroimaging - used to examine the activity of the brain during task performance, and techniques such as transcranial magnetic stimulation, which can safely alter the function of small brain areas to investigate their importance in mental operations.
Computational modeling is a tool often used in cognitive psychology to simulate a particular behavior using a computer. This method has several advantages. Since modern computers are extremely fast, many simulations can be run in a short time, allowing for a great deal of statistical power. Modeling also allows psychologists to visualise hypotheses about the functional organization of mental events that couldn't be directly observed in a human.
Several different types of modeling are used to study behavior. Connectionism uses neural nets to simulate the brain. Another method is symbolic modeling, which represents many different mental objects using variables and rules. Other types of modeling include dynamic systems and stochastic modeling.