Cognitive psychology is the scientific study of mental processes such as attention, language use, memory, perception, problem solving, creativity, and reasoning. Cognitive psychology originated in the 1960s in a break from behaviourism, which held from the 1920s to 1950s that unobservable mental processes were outside the realm of empirical science. This break came as researchers in linguistics and cybernetics, as well as applied psychology, used models of mental processing to explain human behavior. Work derived from cognitive psychology was integrated into other branches of psychology and various other modern disciplines like cognitive science, linguistics, and economics. The domain of cognitive psychology overlaps with that of cognitive science, which takes a more interdisciplinary approach and includes studies of non-human subjects and artificial intelligence. Philosophically, ruminations on the human mind and its processes have been around since the times of the ancient Greeks. In 387 BCE, Plato had suggested that the brain was the seat of the mental processes. In 1637, René Descartes posited that humans are born with innate ideas and forwarded the idea of mind-body dualism, which would come to be known as substance dualism (essentially the idea that the mind and the body are two separate substances). From that time, major debates ensued through the 19th century regarding whether human thought was solely experiential (empiricism), or included innate knowledge (nativism). Some of those involved in this debate included George Berkeley and John Locke on the side of empiricism, and Immanuel Kant on the side of nativism. With the philosophical debate continuing, the mid to late 19th century was a critical time in the development of psychology as a scientific discipline. Two discoveries that would later play substantial roles in cognitive psychology were Paul Broca's discovery of the area of the brain largely responsible for language production, and Carl Wernicke's discovery of an area thought to be mostly responsible for comprehension of language.