Stevens power function
The Stevens power function (after the American psychologist Stanley Smith Stevens ; 1906 - 1973 ) describes as an extension of the Weber-Fechner law the relationship between human sensitivity and stimulus intensity.
Power function
Closer investigations of the input-output functions of sensory systems showed that the logarithmic relationship between sensation intensity (or physiological reaction potential) and stimulus intensity for visual , auditory and olfactory modalities only applies in a small intensity range.
In contrast, the relations can generalize in Stevens 1957 established power function describe:
With
- E = quantity of sensation
- k = constant of proportionality for scaling
- R = stimulus intensity
- R 0 = stimulus threshold intensity
-
n = receptor-specific exponent (with examples)
-
n > 1: reaction amplitude increases disproportionately
- n ≈ 3.5: electrical shocks (60 Hz through fingers)
- n ≈ 1.45: heaviness of weights
- Thermoreceptor
-
n = 1: proportionality of stimulus size and receptor response
- n ≈ 1.0: temperature (cold on the arm)
-
n <1: decreasing increase in reaction
- n ≈ 0.85: vibration (on the finger)
- n ≈ 0.8: taste ( saccharin )
- n ≈ 0.6: loudness (related to sound pressure )
- n ≈ 0.33: brightness with dark-adapted eyes
- n ≈ 0.3: loudness (related to sound intensity ).
-
n > 1: reaction amplitude increases disproportionately
If the estimated intensity and size values as well as the physical stimulus size are plotted in double-logarithmic coordinates, the graphs are straight lines, the slope of which corresponds to the exponent n .
The most important difference between Stevens' power function and Weber-Fechner's law is the methodological difference: Instead of specifying the "just recognizable differences" (difference threshold method), Stevens used a simple subjective (and objective, see below) ratio estimation according to given standard stimuli, which can also be used for complex sensations.
Physiological experiments
Physiological experiments show that this relationship also applies to objective parameters of stimulus processing.
There is a correlation between the discharge frequency of taste afferents and the concentration of taste substances in the form of a potency function. Citric acid and sugar solutions were offered to the test subjects to taste . They had to state how much stronger the test solution tasted compared to the standard solution.
The direct comparison of the subjective and objective stimulus responses was possible because the investigations were carried out in a patient with hearing loss during a middle ear operation ( stapes mobilization) with exposed taste nerves in the chorda tympani (a branch of the facial nerve , VIIth cranial nerve ) under local anesthesia . Action potentials could be derived from these fibers and thus the objective neural response to taste stimuli of different intensity could be compared with the subjective sensitivity levels.
literature
- Stevens, Stanley Smith: On the psychophysical law . In: Psychological Revue . tape 64 (3) , 1957, pp. 153-181 , doi : 10.1037 / h0046162 .