The Role of Psychophysics in Phytopathology: The Weber–Fechner Law Revisited |
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| Authors: | Forrest W Nutter Jr Paul D Esker |
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| Institution: | (1) Department of Plant Pathology, Iowa State University, 351 Bessey Hall, Ames, IA 50011, USA |
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| Abstract: | The accuracy and precision of disease severity assessment data might be improved if there was a better understanding of how
the laws of psychophysics actually relate to the theory and practice of phytopathometry. In this regard, we utilized a classical
method developed in the field of psychophysics (the method of comparison stimuli) to test Horsfall and Barratt’s claim that
raters cannot accurately discriminate disease severity levels between 25% and 50% because, according to the Weber–Fechner
law, visual acuity is proportional to the logarithm of the intensity of the stimulus. We show for two pathosystems, wheat
leaf rust and grapevine downy mildew, that raters can accurately discriminate disease severity levels between 25% and 50%,
and that although Weber’s law appears to hold true, Fechner’s law does not. Furthermore, based upon our results, the relationship
between actual (true) disease severity (X) and disease severity estimated by raters (Y) is linear, not logarithmic as proposed by Horsfall and Barratt. |
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| Keywords: | accuracy Fechner’ s law phytopathometry precision Stevens’ s power law Weber’ s law |
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