The 1950s saw the advent of the cognitive revolution, a time when psychologists began to reject the idea that psychology should only focus on observable behaviour and acknowledged the importance of cognition as a way of understanding behaviour, Cognitive psychologist believe that behaviour is guided by internal mental representations of the world. They acknowledge that although these mental representations cannot be studied directly they can be inferred through measurement of performance on standardised tests of memory and attention for example.
Cognitive psychologists use many research methods including experiments and advances in brain scanning have led to the emergence of cognitive neuropsychology. 

cognitive glossary

cognitive approach handout

key assumptions cognitive

Internal mental processes

Role of schema

Theoretical and computer models

Emergence of cognitive neuroscience