Toward the Science of Psychology:
Early Experimentalists
Dr. Paul Dockree, History of Psychology: PS1203, 2009
Psychology: a subject for scientific enquiry?
•
Two key developments were critical to
the beginnings of psychology as a science
in the 19th century:
1. Advances in physiology and its contribution to
psychology
2. The introduction of quantitative measurements of
mental processes
From Descartes’ “animal spirits” to Bioelectricity
Galvani was the first investigator to appreciate the relationship
between electricity and animation. He discovered that electrical
charges or bioelectricity exists in the body and this may be the means
in which brain/body interactions occur.
Charles Bell (1774-1842)
Francois Magendie (1783-1855)
Diagram of posterior (afferent) and anterior (efferent) spinal roots
Identified by Charles Bell and Francois Magendie
First evidence of different pathways into to the brain for sensing the world and
pathways back out of the brain for responding to the world
REFLEX
THEORY OF
THE BRAIN
Illustration of
the “reflex
arc”: one of
psychology’s
most
persistent
themata
•Sensory areas of brain represented the world
• Association fibres provide the connection between stimulus and response
•Motor areas of the brain controlled the body
Knowing the very basic nature of brain functioning provided a new backdrop for psychology.
What is the speed of conductance of information
in the nervous system?
Hermann von Helmholtz, teacher of Wilhelm Wundt
Measured speed of nervous transmission in frogs and humans.
In 1852 he measured the speed of a nerve impulse.
Helmholtz stimulated a frog’s nerve near a muscle and then farther away.
Impulse velocity within the nervous system was calculated at one tenth the
speed of sound or 26 metres per sec.
Of Frogs and Men
• In comparison with his frog experiments,
Helmholtz's work on humans presented
special challenges
• Simple Reaction Time experiments
• A very weak electric shock was applied to the skin.
Subjects were ask to react with hand movement which
registered time to react.
• He repeated experiments in different subjects. Results
varied between a mean of 0.12 and 0.20 seconds.
Parts of Reaction Time
1.
2.
3.
One part of the time between stimulation and reaction
was consumed by the ‘sending of the signal’ (i.e. the
stimulus) through the sensory nerves.
Another portion of time (which Helmholtz assumed to
be the same time as the first) was needed to transmit
the ‘message’ through the motor nerves to the muscle.
The remaining part of time, Helmholtz concluded, was
the time required ‘in the brain for the processes of
perceiving and willing’
Speed of Nerve Conduction in Humans
• The procedure Helmholtz then used was to stimulate the
human body in different places (e.g. in the toe and the
thigh).
• He could then measure the relative differences in time to
response to a stimuli at different points on the body - the
processing time within the sensory nerves (assuming brain
processes and motor processes to be constant).
• By this method, Helmholtz calculated that RTs were
slower when the toe was stimulated compared to the
thigh – nerve impulses were estimated to travel 50-60
metres per second.
How do we use RTs to quantify mental processes?
Franciscus Cornelis Donders 1818-1889
An early mental chronometer
invented by F. C. Donders to
measure reaction time.The
paper tape below could be used
to measure the time between a
stimulus sound and a reaction
sound. The top line shows the
oscillations of a tuning fork
(which take a known amount of
time); the bottom shows the
time, in distance, between the
spoken stimulus and spoken
response.
F.C. Donders
Donders’ logic of cognitive subtraction allows one to infer the speed of
internal mental processes that are not directly observable.
Donders reasoned that the time needed for a simple detection task
consists of the time it takes to perceive the stimulus plus the time it takes
to generate the response. He then used a “subtractive method” to infer
how much time was needed for intervening tasks, such as identification,
comparison, or other higher-level judgments.
Detection: Press a button when you see a light.
Detection
vs
Discrimination Press button 1 when you see a red
Discrimination:
light, but press button 2 when you see a green light.
Logic of Cognitive Subtraction
Identification Time = Discrimination Task RT – Detection Task RT
Decision process:
what color was the
light that I just saw?
Press button 1 when
you see a red light,
but press button 2
when you see a
green light.
Press a button when
you see a light.
German Psychophysicists
Ernst Weber 1795–1878
Gustav Fechner 1801–1887
Weber and Fechner, creators of the first psychological laws
Detecting Differences
• The first quantitative method of measuring mental process
emerged in the field of astronomy
• How good are we at detecting stimuli and making subtle
judgements about features of the external world?
• Weber was the first physiologist that devised a method
for detecting differences between stimuli
• He examined the minimum amount by which stimulus
intensity must be changed in order to produce a
noticeable variation in sensory experience - the just
noticeable difference (jnd).
Weber’s Law
Standard
Comparison
5
6
1/5 = 0.2
10
12
2/10 = 0.2
20
24
4/20 = 0.2
If you take the difference between the
standard weight and the comparison
weight and divide it by the standard
weight you get a constant This
relationship, known since as Weber's
Law, can be expressed as:
Fechner & Psychophysics
• Gustav Fechner at University of Leipzig working as a
physicist three decades after Weber.
• The relationship between the psychic and the physical and
laws that govern this relationship – Psychophysics.
• Whereas Weber showed that discriminating between
stimuli is lawful, Fechner wanted to explain how our
experience changes with the increasing magnitude of a
stimulus.
Fechner & Psychophysics
• Absolute threshold
• Weber’s principle of the just-noticeable difference or
difference threshold was then used to track sensory
changes with the increasing magnitude of a stimulus.
1. Experimenter sets the
brightness of these lights
to be equal
Sample
Comparison
2. Experimenter gradually changes the
brightness of the comparison light until
the subject says the lights look different
You can plot a curve showing the strength of a sensation
of brightness (in jnds) in relation to the intensity of a
stimulus
Logarithmic relationship between increases in magnitude of
stimulation (on x axis) and noticeable increases in perception (on y axis)
Fechner’s law: As an intensity of a stimulus is increased
linearly the sensation it produces grows logarithmically
Fechner’s agenda, psychology and science
• There is no area of psychology with such basic and
fundamental and lawful relationships as the field of
psychophysics.
• On the issue of whether psychology should aspire to be a
science (defined as establishment of reliable and
reproducible laws) psychophysics comes closest to that
model.
• From psychophysics we have evidence about the absolute
threshold of sensation and how they change with the
physical stimuli in the environment.
Who invented Psychology?
Wilhelm Wundt or Gustav Fechner?
Weber’s and Fechner’s methods
were used extensively in the first
psychological laboratory in the
University of Leipzig founded by
Wundt.
Wundt used and taught many of
the methods discussed: simple
reaction time, complex reaction
time, absolute threshold, just
noticeable difference etc.
However, Wundt also developed
the methods of introspection.