The Enligtenment• Since the Renaissance, Europe undergoes a

gradual change from depending on authority as the source of truth to relying on scientific methodology.

• In full swing by the late 1700s.

• The American Revolution

• Locke and Berkeley– Perception is subjective, not objective

– Cannot assume a one-to-one correspondence between the nature of the physical object and our perception of it

• Scientists began to focus on the physiological processes involved in sensing and perceiving

The Imperfect Human Observer

Physiology of the Nervous System• Luigi Galvani (1737-1798)

– Italian Physiologist

– Identified electricity as the “currency” of the nervous system

– Nephew (Giovanni Aldini) continued the tradition using severed heads of criminals

– More Showmanship than Science

The Electricity Craze

The Guillotine Problem• Theodor Bischoff

– Smelling salts, “Pardon!”– No response– Concluded that bodily twitches

were not conscious

• Robert Whytt (1714-1766)– Extensive study of decapitated

animals– Habit formation– Alluded to Classical Conditioning

Early PhysiologyJohannes Müller (1801-1858)

– 1833-1840: Handbook of the Physiology of Mankind

– Aimed to• Localize functions within the

nervous system• Pinpoint peripheral sensory

receptor mechanisms

Johannes MüllerDoctrine of Specific Nerve Energies

1. The mind is directly aware not of objects in the physical world but of states of the nervous system.

2. “The qualities of the sensory nerves of which the mind receives knowledge in sensation are specific to the various senses, the nerve of vision being normally as insensible to sound as the nerve of audition is to light. “

Paul Broca (1824-1880)– The Clinical Method (1861)

– Broca’s area: the speech center in the 3rd frontal convolution of the left hemisphere of the cerebral cortex

Mapping from the Outside• Franz Josef Gall (1758-1828)

– Used the clinical method to map the brain and confirm:

• Existence of white and gray matter• Fibers from each brain side to the

opposite spinal column side• Fibers connecting the two brain

hemispheres– “How do the size and shape of

the brain reveal information about brain facilities?”

– Can it be mapped from the outside?

Phrenology• J.G. Spurzheim (1776-1832)

– Gall’s student

– Took specific nerve energies a little too far

Pierre Flourens (1794-1867)• Prof. of Natural History-Paris

• Used extirpation (ablation)1. Isolate the parts

2. Remove, when necessary, the entire parts

3. Always prevent the complication of the effects on the lesions due to the effects of effusions.

Pierre Flourens (1794-1867)• Six large functional areas of CNS

1. Cerebral cortex (perception, intelligence, will) 2. Cerebellum (coordination of movements)3. Medulla oblongata (vital center) 4. Corpora quadrigemina (supports seeing)5. Spinal cord (conduction) 6. Nerves (excitation)

• Brain has GROSS specialization, but is probably an interdependent network

Gustav Fritsch and Eduard Hitzig (1870)

• Electrical stimulation method: “A technique for exploring the cerebral cortex with weak electric current to observe motor responses.”

• Stimulation of certain cortical areas results in motor responses such as leg movement

Gustav Fritsch and Eduard Hitzig (1870)–“A part of the convexity of the hemisphere of

the brain of the dog is motor . . . another part is not motor. The motor part, in general, is more in front, the non-motor part more behind. By electrical stimulation of the motor part, one obtains combined muscular contractions of the opposite side of the body. …such facts show that the origin of at least some function of the soul is bound up with circumscribed parts of the brain” - F&H, 1870

–The cerebral hemispheres control voluntary movement

Gustav Fritsch and Eduard Hitzig (1870)

Physiology of the Nervous System• Camillo Golgi (1844-1926)

– Italian neurologist

• S. Ramón y Cajal (1852-1934)– Spanish neuroanatomist– Nobel Prize 1906

Cajal and Others• Accepted as fact by the end of the 19th century:

– Gross anatomy defines the direction of neural information (cell body >>>axon>>>synapse)

– Neuron-Neuron Communication occurs at the synapse

– Discovered the direction of travel for brain and spinal cord nerve impulses

– Nerve fibers = bundles of discrete neurons separated by synapses

– Supported the mechanistic view• Atomistic structures combined to produce

complex complex structure

The Beginnings of Experimental Psychology

Four German physiologists directly responsible for initial applications of experimentation to mind:

1. Hermann von Helmholtz

2. Ernst Weber

3. Gustav Theodor Fechner

4. Wilhelm Wundt

Why Germany?

– German approach to science• Experimental physiology established and

recognized to a unique degree• The German temperament: exactness and

precision• Use of the inductive method• Ready acceptance of biology as a science• Broad definition of science

Germany 1870-1910

• Results– Series of important

discoveries in the sciences

– German university professors directly responsible for growth and development of scientific psychology

Hermann von Helmholtz (1821–1894)

• Born in Potsdam, Germany

• Delicate health

• 1838: enrolled at a Berlin medical institute: free tuition to future army surgeons

• Seven years in the army

– Invented the ophthalmoscope– 1856-1866: Handbook of

Physiological Optics– 1863: On the Sensations of Tone

(research on acoustics)– Also wrote on a diversity of topics

including hay fever, glaciers, geometry

– Indirectly contributed to inventions of the wireless telegraph and radio

Hermann von Helmholtz (1821 – 1894)

The contributions of von Helmholtz– First empirical measurement of the rate of

conduction of the neural impulse (90 ft/sec)– Suggested thought and movement are

successive, not simultaneous– Reaction times for sensory nerves in humans– Studied mechanism by which internal eye

muscles focus the lens– Revised and extended a theory (Young-

Helmholtz) of color vision that correctly predicted three types of cones

Ernst Weber (1795 – 1878)– Born in Wittenberg, Germany– 1815: PhD at university of Leipzig– 1817 – 1871: taught anatomy and

physiology at Leipzig– Primary research interest:

physiology of sense organs– Applied experimental methods to

problems of psychology– Explored new fields: cutaneous

sensations rather than just vision and hearing

Ernst Weber (1795 – 1878)• Thresholds

– Two-point discrimination of the skin

– Predicted layout of sensory cortex

– Just noticeable differences (JND)– Discrimination depends on the relative

difference between and not on the absolute weights of objects

– Weber’s law: a constant ratio for each sense– Perception of a stimulus is not directly

correlated to the physical stimulus

Ernst Weber (1795 – 1878)

Ernst Weber (1795 – 1878)

• The Big Issues– Revealed a way to investigate

the mind-body relationship

– Demonstrated the utility of experimental methods as a means of studying psychological phenomena

Gustav Theodor Fechner (1801-1887)

– Born in southeastern Germany

– 1817: began medical studies at University of Leipzig

– Attended Weber’s lectures on physiology

– Professor at Leipzig

– Episode of Depression followed by euphoria and delusions of grandeur• Developed the idea of the pleasure principle • Concept later influenced Freud

– 1844: officially an invalid, given a pension by university of Leipzig

– Remained at Leipzig in excellent health with continuing important scientific contributions until his death at 86

Gustav Theodor Fechner (1801-1887)

Quantifying Mind and Body1850: While lying in bed had insight about the law

governing the mind-body connection• A quantitative relationship between a mental sensation

and a material stimulus• Effects of stimulus intensities are relative to the amount

of sensation that already exists

Fechner crossed the barrier between body [physical stimulation] and mind [mental sensation] by relating one to the other empirically, making it possible to conduct experiments on the mind.

Proposed two ways to measure sensation

1. Absolute threshold: “the point of sensitivity below which no sensations can be detected and above which sensations can be experienced.”

• Only the lowest level of a sensation can be determined using method of absolute threshold

• Presence or absence of a stimulus

Gustav Theodor Fechner (1801-1887)

Weber’s (Fechner’s) Law: S = K log R

2. Difference Threshold– For each sense, “there is a certain relative increase

in stimulus intensity that always produces an observable change in the intensity of the sensation.”

– S: magnitude of the sensation [the mind or mental quality]

– K: a constant– R: magnitude of the stimulus [the body or

material (physical) quality]– Log: logarithmic relationship

• Psychophysics: “the scientific study of the relations between stimulus and perception”– Method of average error (method of adjustment)

• Over a number of trials, subject adjusts a variable stimulus until it is perceived to be equal to a standard stimulus

• The average of the obtained differences = error of observation

• Used to measure reaction time and visual and auditory discriminations

• Calculating the mean is basically drawing on the method of average error

Psychophysics

– Method of Constant Stimuli• Uses two constant stimuli: a standard weight and a

comparison weight• Goal is to measure the stimulus difference required

to produce a judgment of the second weight as heavier, lighter, or equal to the first weight

– Method of Limits (differential threshold)• Two stimuli such as weights presented to the

subjects• Experimenter increases or decreases one stimulus

until subject detects a difference• Many trials are used, and jnds are averaged

Psychophysics

• In brief, Fechner– Countered the notion that psychology could

never be a science because psychological processes not measurable

– Provided the prerequisites for a science of psychology by making it possible to measure mental experience

– Provoked Wundt’s plan for an experimental psychology

– Gave psychology precise and elegant techniques of measurement

• By the mid 19th century natural science methods were being used to study mental phenomena

• British empiricists outlined the importance of understanding the limitations of the senses

• German physiologists described functioning of the senses and paved the way for Wilhelm Wundt who brought them together by founding psychology