1. Physiology and Psychophysics The origins of experimental psychology can be found in the intersection of physiology (studies of the brain and nervous system) and psychophysics (studies relating physical changes in sensory signals to psychological experience). Early Psychophysics: Friedrich Bessel (1784-1846) first reaction-time studies. Astronomer interested in accurate measurements of star position, movement, etc. Found that measures varied with who was doing the measuring. Derived the "Personal Equation," the effect of the observer's personality and circumstances on astrometrical measurements. Lesson: science cannot avoid subject observer effects. Instead they must be empirically assessed and accounted for in scientific studies. Early physiology: Are nerve fibers hollow tubes carrying animal spirits (Descartes) or vibration conductors from sense organs to brain (Hartley)? Charles Bell 1774-1842) and Francois Magendie (1783-1855) found that they were neither. They were two types: sensory fibers running up the dorsal side of the spine and motor fibers running down the ventral side (Bell – Magendie Law). Note: provided first physio evidence of something speculated by Galen back in first century AD!

2. Physiology and Psychophysics Johannes Muller 1801- 1858: Doctrine of specific nerve energies: subjective sensory experience depends on which sensory fibers are stimulated. Ex: blow to head, push on eye, electrical stimulation of optic nerve, light energy all lead to visual experience. Doctrine of adequate stimulation: All senses are especially suited to process a specific type of physical signal and provide the most compelling experience using that signal. Muller the Kantian: Muller believed his studies of sensory function supported Kant’s view of innate categories. Specific sensory nerves organized inputs according to pre-determined subjective experiences. Hermann von Helmholtz 1821-1894: Student of Muller, but disagreed on the issue of vitalism (a special non-material substance responsible for life). Use studies in conservation of energy to disprove vitalism. Total energy expended by living organism could be accounted for with physical factors (food intake, metabolism, etc.). Successful application of physics to physiology. Another successful application of physics to physiology. Rate of nerve conduction studies. Electrical signals traveled at constant rate along nerve fiber. Larger fibers had faster conduction speeds.

3. Physiology and Psychophysics Young-Helmholtz theory of trichromatic vision. Doctrine of specific nerve energies applied to three different types of cone receptors in the retina of the eye. Pattern across three types of cones leads to subjective experience of color Unconscious inferences: assumptions based on past experience (not innate?) that gave order and meaning to sensory experience. EX: use of retinal disparity to understand depth and distance. Helmholtz believed that UI’s disproved Kant’s innate categories. Resonance place theory of pitch perception (also called place theory or resonance theory). Basilar membrane is varies in width and individual fibers along BM vibrate in resonance with incoming sound wave. These separate vibrations produce different experiences of pitch. Proved to be about half-right.

4. Physiology and Psychophysics Ewald Hering 1834-1918: Disagreed with Helmholtz about color vision. Pointed to color aftereffects as evidence of opponent process functioning in vision. Opponent process theory: cells in LGN and PVC use certain hues as rivals. Equal proportions produce gray experience. Accounts for some color experiences that tri-chromatic has difficult time with Christine Ladd-Franklin 1847-1930: One of the first to proposed an evolutionary theory of color vision. Achromatic vision first, with blue- yellow channel later and red-green channel most recent. Offer evidence from color blindness and deficiency as potential supportive evidence

5. Rise of Phrenology Emerged out of the faculty psychology movement. Faculties were mental abilities or capabilities of the mind (language, mathematics, morality, pattern recognition, etc.). Original faculty psychologists did not claim that these abilities were localized in the brain, but Franz Joseph Gall (1758-1828) did. Why? From his study of animal brains, Gall claimed that brain size was associated with intelligence and specific parts of the brain had specific function. For example grey matter processes information while white matter communicated messages across the cortex. Thus, it seemed logical to him that in humans certain mental abilities associated with intelligence and personality would be localized in specific parts of the brain. Furthermore the size of these local areas could be determined by the bumps and depressions in the skull. From the early 1800’s to 1900’ Phrenology was popular and respected. Why? Fit in with the idea of materialist idea of mind being dependent on brain. Also offered practical applications such as in education where practice in certain mental functions was thought to strengthen those functions (called formal discipline). Faculties were thought of a ‘mental muscles’ that could be strengthened and enlarged.

6. Fall of Phrenology Pierre Flourens (1794-1867) attacks on Phrenology. Using ablation (removal of circumscribed parts of brain) Flourens sought to test phrenology’s claims of localization of function. While some evidence of localization found, Flourens concluded that cerebral hemispheres functioned as a unit, which strongly contradicted basic assumption of Phrenology Not so fast! Using the clinical method (observation of cognitive disorder with post-mortem brain examination) Paul Broca (1824-1888) concluded that the left, inferior frontal lobe was responsible for speech production. This was obviously an example of (more) localized function present in the cerebral cortex. This, however, did little to revive Phrenology given that the speech production area was not where they had predicted. Broca’s other work on brain size and intelligence was more dubious. He believed that he had found evidence of a link (larger brain – more intelligence) but later reviews of his work found contradictions and sloppiness. Carl Wernicke 1848-1905: found analogous area in left superior temporal lobe responsible for speech comprehension.

7. Mapping the brain Using electrical stimulation, David Ferrier (1843-1928) mapped the motor cortex of the monkey. Went on to map other sensory regions such as olfaction, audition, and vision. Decades later, neurosurgeon Wilder Penfield (1891-1976) mapped the human motor cortex. Demonstrating localized function in motor and sensory areas of the cerebral cortex.

8. The First Psychophysicists Ernst Weber (1795-1878). Two-point thresholds: smallest distance between two points pressed against the skin that can be discriminated as two separate points Weber’s law: JND is constant proportion of existing level of stimulation. For example (just making this up), suppose Weber fraction for something is 1/10, then if 10 units of stimulation are present, JND=1, suppose 100 units of stimulation are present, JND = 10. Absolute amount of JND varies, but proportional change remains constant.

9. The First Psychophysicists Gustav Fechner (1801-1887): Spinozian outlook. Formalized the study of psychophysics. Developed specific methodologies for assessing thresholds (absolute and difference). Thought psychophysics would solve M/B problem. It didn’t! Method of limits: start high, descent til change. Start low, ascend til change, repeat, average. Method of constant stimuli: randomly present varied levels of comparison signal judged against standard. Method of adjustment: s controls signal. Adjust up or down to match standard or to make detectable, undetectable. Fechner’s law describes subjective experience of the JND. Explains why JNDs increase in amount as stimulation increases. Why? Because subjective response “slows” as stimulation increases.