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Experimental Psychology PSY 433. Appendix A – Experimental Psychology: A Historical Sketch. 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?

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Experimental psychology psy 433

Experimental PsychologyPSY 433

Appendix A – Experimental Psychology: A Historical Sketch

Origins in philosophy
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.

Physiology changed philosophy
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).

British empiricism
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

Application of scientific method
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.

Helmholtz 1821 1894
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?

Weber 1795 1878
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.

Just noticeable difference jnd
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)

Fechner 1801 1887
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.

Fechner s law
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.

Relationship of jnd to stimulus
Relationship of JND to Stimulus

S.S. Stevens modified Fechner’s Log Law to a Power Function in the early 1950’s.

Wundt ebbinghaus
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.

Stucturalism vs functionalism
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.


  • 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.

Gestalt psychology
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.

The cognitive revolution 1950 present
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.

Cognitive neuroscience
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.


  • 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).