Final answer:
Dr. Hart is engaged in the study of cognition, focusing on how the brain processes and organizes information from senses and thoughts.
Step-by-step explanation:
Dr. Hart's research interests, which include the mental activities involved in processing images, concepts, words, rules, and symbols, would best be described as studying cognition. This field, known as cognitive psychology, focuses on the myriad mental processes associated with thinking, perceiving, planning, and understanding language and memory.
Cognitive psychology is intertwined with the exploration of how our brains integrate and organize information. Researchers in this field are keen to comprehend how we organize our thinking, develop schemata, and how our cognitive processes enable us to function in daily life seemingly without effort. Dr. Hart's research would not center on emotion, instincts, or motivation, but squarely upon the cognitive aspects of psychological study. This involves methodical examination of how thoughts are formed, how decisions are made, and how the brain performs its ceaseless task of processing various forms of information.