PSY 3360 / CGS 3325 Historical Perspectives on Psychology Minds and Machines since 1600

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1 PSY 3360 / CGS 3325 Historical Perspectives on Psychology Minds and Machines since 1600 Dr. Peter Assmann Spring 2019 Franz Gall ( ) Gall postulated that the cerebral cortex serves the highest level of brain function. Analyzed character traits and skulls of famous people and criminals. Generated a list of 27 faculties (including sex drive, maternal behavior, aggression, etc). Launched new science called phrenology. Physiognomy and phrenology Phrenology: surface of the skull mirrors the exaggeration of functional areas in the cortex. Bumps on the skull are associated with faculties that are prominent in individuals. Gall s work foreshadows the idea of localization of function. Paul Flourens ( ) Critic of the phrenology movement Ablation studies of animals Brain lesion studies suggested to Flourens that the cerebral hemispheres function together as a single unit Launched debate over localization of function cranial damage and lesions as a means of studying localization of cerebral function in humans. In 1861 Broca presented a case study of a man with normal cognitive functions in all respects except that he no longer possessed the ability to speak (aphasia). When the patient died, Broca performed an autopsy and revealed a lesion in the middle part of the frontal lobe of the left hemisphere. 1

2 Broca s area: frontal lobe of the left hemisphere Hemispheric lateralization of function language center? cranial damage and lesions as a means of studying localization of cerebral function in humans. In 1861 Broca presented a case study of a man with normal cognitive functions in all respects except that he no longer possessed the ability to speak (aphasia). When the patient died, Broca performed an autopsy and revealed a lesion in the middle part of the frontal lobe of the left hemisphere. Carl Wernicke ( ) In 1874, Carl Wernicke described a different pattern of language breakdown with injury to the temporal lobe of the left hemisphere, which he described as sensory aphasia. Galvani (1780) discovered that a frog s leg would twitch when the inside and outside of the muscle were connected in series with two different metals. Emil du Bois-Reymond ( ) du Bois-Reymond discovered the action potential in 1848 An action potential (or nerve impulse) is a pulse-like wave of voltage that travels along the axon of a neuron. Fritsch and Hitzig (1870) showed that electrical stimulation of regions of the cortex in dogs produced specific responses of individual muscle groups (motor strip). 2

3 Lashley ( ) coined the term equipotentiality to describe the capacity of an intact part of the brain to take over the (memory) functions of an damaged portion. Wilder Penfield ( ) famous neurosurgeon; leading authority on epilepsy Electrical stimulation of the cerebral cortex in awake patients (prior to surgery) could produce complex perceptions or motor actions homunculus (cartoon map of motor cortex) Rise of psychophysics German physiologist Contemporary of Johannes Müller Studied tactile perception (pressure, temperature, pain) and kinesthesis (muscle sense) absolute threshold differential threshold just noticeable difference (jnd) Two-point threshold Weber found that the smallest perceptible change in a stimulus is a constant fraction of the magnitude of the original stimulus: I / I = k 3

4 Weber s Law: the jnd for detecting a change in intensity is proportional to the intensity of the standard stimulus. Theory and methods of psychophysics Double-aspect monism Mapping the functional relationship between physical and mental worlds. Quantitative measurement of mental processes. Outer Psychophysics Stimuli Sensation Inner Psychophysics Brain Processes The Problem: Physical objects and events are external, public, objective, open to direct measurement. Mental processes are internal, private, subjective, and cannot be measured directly. Need for an indirect method. Elemente der Psychophysik (1860) Complementary colors and subjective afterimages Inner and outer psychophysics Fechner s law of intensity: Perceived intensity is equal to the logarithm of the stimulus intensity times some constant k. Fechner discovered that the relationship between physical and perceived intensity had been previously described by Weber. He renamed it Weber s Law. 4

5 Fechner's Law: S = k log P wherep is the physical stimulus, S is the perceived intensity, and k is a constant. Weber fraction: just noticeable differences (jnd s) correspond to constant ratios. Psychophysical Methods Fechner developed three methods for measuring sensory thresholds: Method of limits Method of constant stimuli Method of adjustment 20 th century developments Steven s power law Ψ(I) = k I a Signal detection theory 5