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

Luigi Galvani (1737 –1798) discovered that muscle and nerve cells produce electricity

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.

From Descartes’ “animal spirits” to Bioelectricity

Diagram of posterior (afferent) and anterior (efferent) spinal roots Identified by Charles Bell and Francois Magendie

Francois Magendie (1783-1855)

Charles Bell (1774-1842)

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 bodyKnowing the very basic nature of brain functioning provided a new backdrop for psychology.

Hermann von Helmholtz, teacher of Wilhelm WundtMeasured 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.

What is the speed of conductance of information in the nervous system?

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. 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.

2. 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.

3. 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.

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.

Franciscus Cornelis Donders 1818-1889

How do we use RTs to quantify mental processes?

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.

F.C. Donders

Detection vsDiscrimination

Donders’ logic of cognitive subtraction allows one to infer the speed of internal mental processes that are not directly observable.

Detection: Press a button when you see a light. vsDiscrimination: Press button 1 when you see a red light, but press button 2 when you see a green light.

Identification Time = Discrimination Task RT – Detection Task RT

Press a button when you see a light.

Press button 1 when you see a red light, but press button 2 when you see a

green light.

Decision process: what color was the light that I just saw?

Logic of Cognitive Subtraction

Weber and Fechner, creators of the first psychological laws

German Psychophysicists

Ernst Weber 1795–1878 Gustav Fechner 1801–1887

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

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:

Standard

5

Comparison

6

10

24

20

12

1/5 = 0.2

2/10 = 0.2

4/20 = 0.2

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.

Sample

Comparison

1. Experimenter sets the brightness of these lights to be equal 2. Experimenter gradually

changes the brightness of the comparison light until the subject says the lights look different

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

You can plot a curve showing the strength of a sensation of brightness (in jnds) in relation to the intensity of a stimulus

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.