Make your own free website on Tripod.com

History & Systems of Psychology
Chapter 8 – Early Experimental Psychology

Objective & Subjective Reality
Scientific advances and study of philosophical questions raised questions of objective & subjective reality – How do we know the physical world?
Question of mechanism by which empirical events are represented in consciousness
Intense study of sensory perception & other aspects of nervous system gave birth to experimental psychology

Early Research on Nervous System
Bell-Magendie Law: demonstrated the different paths and functions of sensory & motor nerves
Significant because it demonstrated specific mental functions are mediated by different anatomical structures
Muller’s doctrine of specific nerve energies: demonstrated each of 5 types of sensory nerves responds in a characteristic way regardless of stimulation

Early Research on Perception Hermann von Helmholtz (1821-1894)
Opposed vitalism & idea of “life force,” was a materialist (all of life can be explained in terms of physical & chemical processes)
Measured speed of nerve conduction, demonstrating it was not accomplished through a mysterious (nonphysical) force
Work on senses included:
Theory of color vision: color is not inherent in various light wavelengths, there are 3 color receptor types on the retina
Theory of auditory perception: ear not a single sense receptor but a highly complex system of many receptors sensitive to different frequencies

Helmholtz, continued
Theory of Signs:
Believed in an active mind (German rationalist heritage)
The mind’s task is to create a reasonably accurate conception of reality from the various “signs” it receives from the body’s sensory systems.
There is a dynamic relationship among volition, sensation, and reflection as the mind attempts to create a functional view of external reality.

Early Work on Brain Functioning
Franz Gall & phrenology – discredited, but did establish idea of localization of function within the brain
Flourens used ablation method to investigate localization of function
Broca & Wernicke used clinical method to localize language functions in the brain
Others used electrical stimulation to identify crucial areas

Ernst Weber (1795-1878)
Investigated sense of touch, mapped the sensitivity of the body using a 2-point threshold
Identified the just noticeable difference (jnd): smallest amount of change necessary to notice a difference between two stimuli
Weber’s law quantifying the jnd was the first formula in psychology. It showed a systematic relationship between physical stimulation & a psychological experience (perception of the stimuli).

Gustav Fechner (1801-1887)
Interest in mind-body issue led to study of psychophysics (study of relationship between physical & psychological events)
Refined Weber’s law, arrived at Fechner’s law, which showed that mental perceptions are a logarithmic function of physical stimuli
Studied absolute & differential thresholds

Fechner, cont.
Absolute threshold: the smallest (or greatest) amount of stimulation that can be detected
Ex: the lowest and highest number of watts or decibels that the human eye or ear can detect
Differential threshold: the amount that stimulation needs to change before a difference in that stimulation can be detected
Ex: whether the eye can detect a change from 40 watts to 42 watts

Fechner’s Methods
Method of limits or method of jnd:
Absolute: a stimulus is varied to determine limits of detection ability
Differential: stimulus is varied and compared to a standard, to determine at what point the subject can detect a difference

Fechner’s Methods, cont.
Method of constant stimuli (for differential thresholds):
pairs of stimuli are presented, one constant and one variable
Subject reports whether the variable stimulus appears to be less than, equal to, or greater than the constant

Fechner’s Methods
Method of adjustment (for differential thresholds):
Subject has control over the variable stimulus and is to change it to match the standard stimulus