Introduction
Although early modern natural philosophers were interested in the relationship between biological and psychological processes, psychology remained a branch of philosophy or theology. Then nineteenth-century physiologists demonstrated experimentally that neuromuscular functions, perceptual processes, and mental operations were interdependent, a consistent finding that created space for a natural-science psychology. Some German scholars, then British, French, US, and Russian scientists began to adopt physiologists’ methodology to analyze conscious experience of sensory-motor functions and answer such philosophical questions as:
What is a mind? Of what does it consist? How is it related to the brain?
What roles do biology and evolution play in psychological processes?
How do psychological capacities develop?
How do humans gain knowledge of the empirical world? How do physical phenomena become sensations? How do emotions and thoughts originate?
What is an action? How is action related to emotion, thought, and will?
How do humans remember their experiences?
What is a self? How is it related to other selves?
What is the individual’s relation to society?
In answering these questions many new psychologists used extant language concerning brain–behaviour relations and evolutionary adaptation. They adopted biological notions, expounded by Alexander Bain and Herbert Spencer, about cerebral localization, sensory-motor activity, and the association of ideas (R. M. Young, 1970). In addition, Gustav Fechner’s psychophysics, “the institutionalization of laboratory instruction” (Ash, 2003, p. 253), and British innovations in statistical analyses of population data became the components of natural-science Psychology’s methodology.
But early psychologists encountered a problem: they could only provide functional explanations according to physiological sensations and movements, not across all levels of brain and behavioural relations. Thus, while scholars struggled with the insufficiency of purely physiological, contemporary explanations for psychological phenomena, the discipline of Psychology took shape.