Experimental Psychology PSY 433

1. Experimental PsychologyPSY 433 Appendix A – Experimental Psychology: A Historical Sketch

2. Origins in Philosophy • Mind-body problem – are the mind and body the same or different? • If they are different substances, how do they interact or communicate? • Dualism – mind (soul) is not governed by physical laws but possesses free will. • Descartes – mutual interaction. • Animals do not possess souls and can be studied because they are physical.

3. Rene Descartes (1596-1650)

4. Physiology Changed Philosophy • Localization of cerebral function by physiologists showed that the brain is the organ of the mind. • Mental states were shown to affect the body. • Trauma, mesmeric trance, mental suggestion. • Huxley’s “Epiphenomenalism” – mental states have no causal efficacy, like paint on a stone (neurophysiology is the stone, mind is the paint).

5. British Empiricism • Locke, Berkeley, Hume, Hartley • Mind may follow laws and thus be modeled just as the physical world is. • Elements (ideas) • Forces (associations between ideas) • Tabula rasa – mind is a blank slate written upon by experience. • Mental activity may be mechanical: • Mind as a machine

6. Application of Scientific Method • Philosophy uses different methods than psychology: • Anecdote, reflection, logic • Experimental psychology emerged out of the study of sensation, applying laws of physics and chemistry. • Now called psychophysics • “Application of scientific method to the problem of mind” created experimental psych.

7. Helmholtz (1821-1894) • Used experimental methods to study vision and audition. • Reaction times were used to determine the speed of neural impulses. • Test response-times for stimuli from the shoulder and from the ankle. • Nerve impulses are slow – 50 meters per sec. • Reaction times vary considerably across individuals and across trials – how is precise measurement possible?

8. Weber (1795-1878) • Weber studied perceptions of weight and tried to relate these to actual physical weight. • Weight is an objective physical property of objects. • The greater the weight, the greater the difference between it and a heavier weight must be in order to be detectable. • Weber’s Law -- Just-noticeable difference (JND) is a constant across a sensory modality.

9. Just Noticeable Difference (JND) • How much must a stimulus change in order for a person to sense the change. • This amount is called the just noticeable difference (JND) • The actual size of the JND aries with the size of the weights being compared. • JND can be expressed as a ratio: where R is stimulus magnitude and k is a constant and DR means the change in R (D usually means change in science)

10. Fechner (1801-1887) • Tried to relate physical properties to psychological sensations: • Related the objective to the subjective. • Fechner’s Law – each JND corresponds to one subjective unit of measure on a rating scale • This relationship can be described mathematically. • Credited with founding psychophysics.

11. Fechner’s Law • Fechner called Weber’s finding about the JND “Weber’s Law.” • Fechner’s formula describes how the subjective sensation is related to increases in stimulus size: where S is sensation, k is Weber’s constant and R is the magnitude of a stimulus • He also used catch trials to study guessing.

12. Relationship of JND to Stimulus S.S. Stevens modified Fechner’s Log Law to a Power Function in the early 1950’s.

13. Wundt & Ebbinghaus • Wundt (1832-1920) organized psychology and helped to establish it as an independent discipline. • Wrote “Principles of Physiological Psychology” • Did not believe higher mental processes (memory, thought, creativity) could be studied experimentally. • Ebbinghaus (1850-1909) demonstrated that memory could be studied experimentally.

14. Stucturalism vs Functionalism • Structuralism – focused on the contents of mind. • Sensations, images (ideas), affections • Used introspection to identify basic elements. • Introspection proved to be an unreliable method. • Functionalism – focused on the adaptive function of psychological processes within a context. • Not much experimental work done.

15. Behaviorism • Rejected structuralism and functionalism. • Both referred to mentalistic contents of mind that could not be directly observed. • Emphasized focus on relating behavior to evoking stimuli and contexts. • Radical behaviorists: • Watson • Skinner • Now nearly all experimental psychologists are behaviorists to some extent.

16. Gestalt Psychology • Reaction against structuralism. • Whole is greater than the sum of its parts. • Complex mental phenomena cannot be understood by examining elements. • Wertheimer’s demonstration of shape constancy seemed incompatible with structuralism. • Influential in cognitive psychology.

17. The Cognitive Revolution (1950-present) • Using scientific methods to study mental processes that are linked to observable behaviors • The mind actively acquires information, and stores, retrieves, and uses knowledge • Influenced by the computer analogy and information processing theory.

18. Cognitive Neuroscience • Psychophysiology – intersection between psychology and physiology. • Neuroscientists team with psychologists using imaging techniques (PET, fMRI) to study cognitive activity. • Such results must be interpreted with caution • Observing that activity is occurring does not necessarily tell you what kind of activity is happening.

19. Specialization • Today psychologists tend to identify more with areas of interest than with schools of thought (behaviorism, gestalt). • Specialization is the mark of a maturing science. • Experimental psychology is one of 54 divisions in the APA (Division 3). • Other societies: Psychonomic Society, APS, Society for Cognitive Neuroscience, society for Research in Child Development (SRCD).