Robert L. McBride

A JND-scale/category-scale convergence in taste.

The Weber fraction for the sweetness of sucrose was determined at six concentrations. The results provided good support for Weber’s law except for deviation near threshold, a finding consistent with previous work. Consequently, the JND scale approximated to Fechner’s law. The psychophysical function for sucrose sweetness was also obtained by category rating, with precautions taken to preclude methodological bias. This function was likewise found to conform to Fechner’s law, suggesting a JND-scale/category-scale convergence. This convergence was further supported by experiments with the taste stimuli citric acid (acid/sour), sodium chloride (salty), and caffeine (bitter), which showed that the indirectly derived JND scale provides the same measure of taste intensity as the scale obtained directly by category rating.

Perceptual integration of tertiary taste mixtures

Integration psychophysics was used to explore the taste perception of mixtures of sucrose, fructose, and citric acid. Three levels of each stimulus were varied in a 3 × 3 × 3 factorial design. Subjects rated total intensity, sweetness, and acidity of the 27 mixtures on graphic rating scales. Consistent with earlier work, the perceived total intensity of the tertiary mixtures was found to be dictated by the intensity of the (subjectively) stronger component alone (i.e., either the integrated sweetness or the acidity, whichever was the more intense). In contrast, the sweetness and acidity of the mixture were susceptible to mutual suppression: Sweetness suppressed acidity, acidity suppressed sweetness. There was, however, a difference between sucrose and fructose in their interactions with citric acid, fructose being the more susceptible to suppression. This selectivity of suppression indicates that the two sweetnesses could not have been inextricably integrated. Implications for taste coding are discussed, and the findings are reconciled in terms of two separate coding mechanisms: one for taste intensity, another for taste quality.

Category scales of sweetness are consistent with sweetness-matching data

Category scales were obtained for the sweetness of sucrose, fructose, and glucose, with care being taken to preclude methodological bias. These category scales were then used to predict the outcome of scale-free sweetness matching with the same three sweeteners. The matching concentrations predicted from the category scales were found to agree well with those actually obtained in several sweetness-matching studies.

Taste intensity and the case of exponents greater than 1

The magnitude estimation of taste intensity has often produced exponents greater than 1, suggesting that the perceived intensity of some taste stimuli increases at a faster rate than does stimulus concentration, i.e., the psychophysical functions are positively accelerating. However, a reanalysis of published data reveals that when these magnitude scales are replotted in linear coordinates, instead of the conventional log-log form, there is often no evidence of positive acceleration and the numerical value of the exponent bears no reliable relationship to the shape of its psychophysical function. Reasons for this finding are discussed and the implications for taste research are noted.