Physiological Influences on Psychology - Ch3 - History of Modern Psychology - Schultz & Schultz

Frederick Bessel, an astronomer, identified individual differences in measurement, emphasizing the human observer's role. Johannes Müller's 'law of specific nerve energies' proposed that perception's nature is defined by the sensory information pathway, demonstrated by rubbing eyes and seeing light due to optic nerve stimulation.

Flourens used extirpation (brain lesioning) on pigeons to map cerebral functions (higher mental processes), midbrain (visual/auditory reflexes), cerebellum (coordination), and medulla (vital functions). Paul Broca's clinical method, studying patients with expressive aphasia, correlated speech difficulties with lesions in the left hemisphere's third frontal convolution. Fritsch and Hitzig used electrical stimulation to induce movement in animal limbs. In contrast, Franz Gall's phrenology (cranioscopy) claimed skull shape revealed personality and intellectual traits, though it was largely discredited and exploited for profit by his students.

Luigi Galvani hypothesized and demonstrated that nerve impulses are electrical through experiments with twitching frog legs. His nephew, Giovanni Aldini, captivated audiences by reanimating severed criminal heads with electricity, influencing Mary Shelley's Frankenstein. Alessandro Volta's invention of the electric battery provided scientists with an in-lab electricity source. Santiago Ramón y Cajal discovered the directional travel of nerve impulses, earning him a Nobel Prize in 1906.

Germany became the epicenter of experimental psychology due to its broad definition of science, encompassing disciplines beyond just physics and chemistry. German universities championed academic freedom, allowing professors to research freely. The large number of German universities, in contrast to other nations, also provided more opportunities for research scientists to make a comfortable living and train graduate students.

Hermann von Helmholtz, a leading 19th-century scientist, advanced psychology through his mechanistic approach, viewing sense organs as machines. His contributions include measuring the speed of neural impulses (90 ft/sec), developing the Young-Helmholtz trichromatic theory of color vision, and conducting extensive research on audition regarding tone perception and resonance.

Gustav Fechner, having overcome a period of depression, had a pivotal insight on October 22, 1850. He proposed a quantitative relationship between mental sensation and material stimulus, where an increase in stimulus intensity doesn't lead to a one-to-one increase in sensation. Fechner developed methods to measure sensation, including the absolute threshold (minimum intensity for sensation) and the differential threshold (least change in a stimulus causing a change in sensation). He formulated Fechner's Law (S = K log R), establishing a logarithmic relationship between stimulus magnitude and sensation magnitude. Fechner's 1860 book, 'Elements of Psychophysics,' was instrumental in demonstrating that psychological phenomena could be studied experimentally and quantitatively, inspiring Wilhelm Wundt to develop experimental psychology.

Ernst Weber's research focused on muscular and skin senses. He introduced the 'two-point threshold' (the minimum distance for two stimuli to be perceived as separate) and the concept of 'just noticeable differences' (JNDs), identifying the smallest detectable difference between stimuli. Weber found JNDs to be a constant ratio, demonstrating that the amount of difference perceived depends on the initial stimulus intensity.