The Stevens law and the derivation of sensory perception

The Stevens law, S = kIn, is commonly accepted as a landmark achievement in the field of sensory psychophysics and has been widely applied in food sensory research. The theory effectively links the two parameters of very different nature, the intensity of sensory perception (S) and the intensity of physical stimulus (I). However, the Stevens law suffers from two major drawbacks. The equation was self-inconsistent in terms of the units, which makes equation questionable in principle. The Stevens law was also found inapplicable when multiple physical stimuli are involved in the perception of a sensory attribute. To solve the first drawback, we propose to replace the absolute stimulation intensity in the Stevens law with a relative intensity, S = k(I/I0)n. The modified Stevens law becomes self-consistent when both sides of the equation are dimensionless and the theory is applicable regardless of the unit of the physical stimulus. To solve the second drawback, a concept of sensory derivation is introduced and so sensory properties can be categorized as primary sensory and derived sensory. The former can be described effectively by the Stevens law, while description of the latter is beyond the applicability of the Stevens law because of the involvement of multiple sensory stimuli or multi level sensory derivation. Furthermore, a sensory hierarch is constructed with sensory perception of different nature at different levels, including the primary sensory at the basic level and derived sensory perception at progressing levels. The modified Stevens law provides a self-consistent model for psychophysical analysis of sensory perception. The proposed sensory hierarchy helps to streamline sensory terms and attributes and may be used as a useful guide in establishing instrumental analysis of sensory perception.