Psychophysics
•	Johann Friedrich Herbart (1776-1841)
•	Ernst Weber (1795-1878)
•	Gustav Theodor Fechner (1801-1887)
Herbart: From Philosophy to Science
•	Life
•	1776-1841
•	Influenced by Kant and then Leibnitz
•	Succeeded Kant at Konigsberg
•	Importance
•	First text with psychology in title (1816)
•	Influence on educational issues
•	Major transition between philosophy and science
Herbart’s Conception of Psychology
•	Followed Kant that no experimentation in psychology
•	But disagreed with Kant on measurement
•	Newtonian
•	Ideas are ideal points
•	And math can describe their movement
•	Relatively sophisticated notions of measurement and combination of ideas
Herbart’s Theory of Mind
•	Rationalist
•	Apperceptive mass
•	Content of attention
•	Combination of compatible ideas
•	Schema like
•	Relationship of ideas anticipated Gestalt
•	Thresholds of limens of consciousness
•	Leibnitz
•	Influence of ideas on one another determine consciounsess

Contributions of Ernst Weber (1795-1878)
•	Important research on touch and sensation
•	Interested in thresholds
•	Important issue for touch
•	Muscle sense
•	Two-point thresholds
•	Discriminating two points on body
•	Varied according to part of the body
The Weber Equation
•	A just noticeable difference (JND) was a constant proportion of difference to focal stimulus
•	Bigger differences for large as opposed to small stimuli

Gustav Theodor Fechner (1801-1887)
•	Life
•	General Philosophy
•	General Program
•	Importance
Fechner’s Life
•	Studied medicine
•	Important discoveries on physics
•	Taught physics at Leipzig (Weber’s university)
•	Blind after studying after-images of sun
•	Nervous breakdown
Fechner’s General Philosophy
•	Materialist
•	Mental life as function of organization and complexity of objects (material)
•	Thus all objects have some mental life – Leibnitz
•	Dualist but sought absolute identity of mental and physical
Fechner’s General Program
•	Show identity of mental and physical
•	Problem
•	Cannot measure mental life
•	Nor get at biology underlying mental life
Two kinds of psychophysics
•	Inner
•	Relating mental events to biology
•	But can’t get at biology
•	Outer
•	Relationship of physical stimuli to thoughts
•	Physical events can be measured
•	Principle of conservation suggested basic proportionality between physical and brain
The General Equation
•	Sensation is function of brain
•	Brain processes are function of physical stimulus

The Measurement Problem
•	Know that here is a lawful relationship between stimuli and difference thresholds
•	Assumed each sensation made up of small increments (Leibnitz)
•	Through calculus gets the fundamental equation

Importance
•	Showed precise relationship between mind and physical events
•	Only a short step then to experiments
•	Physical events can be measured
•	And manipulated
•	And unconscious
•	If R = 0 (at threshold)  then S = 0
•	But below threshold R is negative so S could be negative