Experimental psychology is a branch of psychology that uses scientific methods to investigate the causes and effects of human and animal behavior. Experimental psychologists design and conduct experiments to test hypotheses about various psychological phenomena, such as sensation, perception, memory, cognition, learning, motivation, emotion, development, social behavior, and biological processes. Experimental psychology aims to discover the underlying mechanisms and principles that govern behavior and mental processes, and to apply this knowledge to solve real-world problems.

Experimental psychology has a long and rich history, dating back to the 19th century when pioneers such as Wilhelm Wundt, Charles Bell, Ernst Weber, Gustav Fechner, and Charles Sanders Peirce established the first laboratories and methods for studying psychology experimentally. Since then, experimental psychology has expanded into many subfields and applications, such as cognitive psychology, behavioral psychology, social psychology, developmental psychology, clinical psychology, educational psychology, and neuropsychology. Experimental psychologists use a variety of techniques and tools to measure and manipulate behavior and mental processes, such as chronoscopes, stereoscopes, kymographs, galvanometers, olfactometers, mazes, electroencephalographs (EEG), functional magnetic resonance imaging (fMRI), positron emission tomography (PET), eye tracking, and more.

Experimental psychology is based on several key assumptions and principles that guide its research methods and interpretations. Some of these are empiricism, testability, determinism, parsimony, operational definition, reliability, validity, and scales of measurement. Experimental psychologists use various types of research designs to control for confounding variables and to test for causal relationships between independent and dependent variables. Some of these are one-way designs, factorial designs, within-subjects designs, and between-subjects designs. Experimental psychologists also use various types of statistical analyses to test their hypotheses and to draw conclusions from their data.

Experimental psychology is a dynamic and evolving field that contributes to the advancement of psychological science and its applications. Experimental psychologists work in academic settings, research institutes, government agencies, health care facilities, educational institutions, industries, and other organizations that require scientific knowledge and skills. Experimental psychologists also collaborate with other disciplines such as neuroscience, computer science, engineering, medicine, sociology, anthropology, linguistics, philosophy, and more. Experimental psychology is a challenging but rewarding career that offers many opportunities for discovery and innovation.