Experimental PsychologyPSY 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? 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.

Rene Descartes (1596-1650)

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

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

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)

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 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)

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 R means the change in R ( usually means change in science)

kR

R

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 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.

RkS log

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 (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

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.

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.

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) 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

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.

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).