This is the 2007 version. Click here for the 2017 chapter 01 table of contents.

Classic Psychophysics

A more reputable early ancestor of psychology, still taught in upper level courses in psychology departments, is psychophysics. We will discuss the modern version of it in Chapter 4, in the section titled Psychophysics and Signal Detection. The word psychophysics refers to the interaction of the mind (psyche) and the physical world (physics). Psychophysicists were interested in how information from the physical world (such as light and sound) was translated into mental experience (such as the perception of brightness and loudness).

What was the concern of psychophysics? What positive influence did psychophysics have upon psychology?

In the history of psychology, psychophysics was important because it was rigorous and scientific, unlike much of early psychology, and because it stimulated much research, resulting in the formation of the first psychological laboratories. A book about psychophysics by Gustav Fechner, published in 1869, is widely considered to have launched modern experimental psychology.

Using instruments available in the mid-1800s, psychophysicists tried to answer questions like these:

What sorts of questions did psychophysicists ask?

1. What is the smallest unit of energy a person can detect? (For example, what is the dimmest light one can detect?)

2. What is the smallest change of energy a person can detect? (For example, what is the smallest change in the loudness of a sound that a person can perceive?)

Psychophysics relied heavily upon graphs and equations. The shiny brass instruments used by psychophysicists (and the equations) seemed impressive and intimidating to beginning students. William James wrote in 1876:

What was William James's opinion of psychophysics, in 1876?

It is more than doubtful whether Fechner's "psychophysic law" of any great psychologic importance... but because these things are very difficult and very "scientific," people...will distrust all teachers who have not swallowed and assimilated them. (p.47)

In other words, psychophysics was very impressive (partly because it was difficult to understand) but it did not seem to have much practical relevance to psychology. Nevertheless, psychophysics endured. With the development of the Theory of Signal Detection in the 1960s, psychophysics achieved a new level of sophistication and relevance. Psychophysics became more relevant to "psychologic" issues and was used for such purposes as evaluating acupuncture, designing human/machine interfaces, and analyzing the performance of audio systems (see Chapter 4).

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