Psychophysics, definition

In contrast to the mechanical and rheological properties of materials, which have defined physical meanings, no such definitions exist for the psychophysical assessment of equivalent textural properties of foods. To identify material properties, or combinations of these, which are able to model sensory assessments requires a mixture of theory and experimentation. Scientific studies of food texture began during the twentieth century by the analysis of the rheological properties of liquid or semi-solid foods. In particular Kokini14 combined theoretical and experimental approaches in order to identify appropriate rheological parameters from which to derive mathematical models for textural attributes of liquid and semi-solid foods, namely, thickness, smoothness and creaminess. 

The 1992 Merbs Nathans paper addresses anomalous color vision based on a dichotomy, the possible complete absence of either the L-channel or M-channel chromophores of vision192. Their definition of a complete deutranope as one completely lacking a green, or M-channel, chromophore does not conform to the original definition of the term or as it is used in this work (Section 18.1). No report has been found in either the electrophysiological or psychophysical literature of any sighted human, color-blind or not, who totally lacked an operational M-channel in his visual system. At photopic levels of illumination, the most chromatically limited deutranope exhibits a luminous threshold function within the normal statistical variation of color normals. 

An Introduction to Color (Evans, 1948), presented in nonmathe-matical terms, is especially useful in its discussion of color perception and of the distinction between color as calculated in psychophysical terms and color as perceived by the mind. This author points out that a colored object or scene may yield knowledge, create an illusion, or even involve hallucination. Such experiences are explained simply by Evans as follows when we think we know the color of an object, we do not look to verify the assumption. Consequently, we can be victims of a genuine hallucination. The observer does not look at the stimulus but relies on his memory. It is important to realize that the definition of color psychophysically is in essence a definition of what a carefully standardized eye receptor is presumed to record in response to a given stimulus, under prescribed conditions, and has nothing to do with how it may be interpreted by the brain. 

The latest of the five treatises discussed here is entitled The Science of Color by the Committee on Colorimetry of the Optical Society of America (1953). A slight letdown is possibly inevitable, which a rereading does not entirely banish. The report is designed to include an elementary discussion to attract and hold the attention of casual readers, with a gradual transition to more advanced exposition. The food technologist tackling the psychophysics of color is apt to be impatient when confronted with distinctions between operational and relational definitions. He learns that the use of quantitative concepts would specialize the relational definitions in an undesirable manner loc. cit, p. 220). Continued study makes the reader more aware of the problems facing the Committee. Is color to be defined as a sensation or in terms of perception How many attributes of color are to be admitted ... 

The main parameters to describe light-related phenomena are classified as radiant quantities and luminous quantities the latter are psychophysical parameters. Table 2 shows their definitions and units. 

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