[Psychophysics of sweet taste. I. Goals and methods of investigation]

[The psychophysics of sweet taste. 8. Interindividual variability of differential findings]

Contribution to the psychophysics of sweet taste. Part 8. On the inter-individual variability of the difference sensitivity. The variability of sensitivity of volunteers is a considerable imponderability for the comparison of sensoric results. The paper deals with the quantitative determination of the different sensitivity of sweet taste of 132 persons, 38 men and 94 women at the age of 19 to 64 years, using a statistically defined method. The numbers of errors are estimated for each person by means of one test difference of two saccharose concentrations using 10 pairs of comparisons and 4 runs. The average number of error of 10 comparisons corresponds to the individual measure of sensitivity. The medium value of the total distribution is 1.54 and the standard deviation is 1.19 errors. The value is only less above the binomial calculated number. In random test women show in comparison to men a significant higher variance at the statistical identical mean. A variance analysis based on the cutting of the distribution edges in the range of 0.5 to 4.0 errors can detect high significantly the steady learning effect of the volunteers during the runs. The method is applicable to determine classified subjective characteristics. The calculations of necessary group numbers for such experiments on the base of binomial distribution are discussed.

[The psychophysics of sweet taste. 6. Context effects by use of multiple stimuli sequences]

For the determination of differentiation probabilities in a multiple experimental design the range of stimuli is a significant source of disturbance. In order to determine their efficiency, sequences with 5 equidistant gradated concentrations of sucrose were used, which were compared with a basic concentration. The probability for each gradation was carried out with help of 2-AFC-technique (60 pairs each). 5 gradations at 3 basic concentrations with fixed, average balance were examined in a factorized experimental design. The frequency of the correct judgments is linearily dependent on the sequence of stimuli. In the experimental space the slope of this relationships decreases with increasing gradation hyperbolically (range-effects). The level of the basic stimuli is in this view without any greater importance. When determining the difference thresholds these context effects are to be considered.

[The psychophysics of sweet taste. 5. The use of a sequential staircase method for the determination of equally intense concentration pairs]

The suitability of a sequential staircase-method for the determination of equal stimuli of the gustatory sense is experimentally investigated. The aim is the decrease of experimental expenditure when ruling sources of bias. In order to realize them sucrose solutions are used both for the constant stimulus and also for the sequence of stimuli. Possible factors are the gradation of the sequence of stimuli and its displacement towards the constant stimulus. These are factorized in a two-staged trial arrangement and are interpreted in a form of an analysis of variance. The gradation of sequence (grain) is the key factor. It defines both the occasional bias and also the efficiency of systematical sources of bias. Thus the subject-depending judgement errors, which occur in larger gradation, are avoidable with their adjustment on the half of the difference threshold. The errors, which are due to the direction, are counterbalanced through an up and down trial execution with a following meaning average. A remaining influence of the displacement of sequence is normally neglective. The standard deviation for the single determination lies--independently of the concentration level--dimensionally slightly above the half of the setting grain. The method of constant stimuli requires at least the twofold experimental expenditure for a similar result.

[Psychophysics of sweet taste. II. Statistical theory of the stimulus-response behavior of sweet taste receptors]

Considering various conditions of adaptation, the authors determined the Weber discrimination thresholds for the sweet taste of saccharose. When the adaptation to the basic stimulus is maintained and use is made of the differential coefficient behaviour, the discrimination threshold is an exponential function of the concentration. The discrimination threshold is by definition that amount of stimulant per unit of volume which will produce an effect of the magnitude of 1. Consequently, the numbers of moles being substituted, its reciprocal, the probability of obtaining a stimulus response, is greater than 1. A differential equation, namely (formula: see text), can be formulated as the basis of the stimulus-response behaviour of saccharose, the integration of which yields a discrimination characteristic expressed as (formula: see text). S = concentration of the solution as the stimulus intensity; R = stimulus response expressed in steps. The parameter b is the maximum probability of the stimulus response and can be termed substance-specific concentration coefficient. Rm is the maximum step number when the stimulus intensity tends to infinity; it is also substance-specific. As this characteristic involves both the proportional factors and the differential coefficients, it is called P-D characteristic. From this invariant relationship, the static P characteristic for a very slow increase in stimulus intensity can be derived. When the adaptation to the basic stimulus is abolished by mouth rinsing between tests in paired comparisons, the dependence of the discrimination threshold on the concentration is more than exponential. The stimulus-response characteristics obtained with different time-courses of stimulation are approximated by both the Weber-Fechner and the Stevens law.