Pleasure and preference in a two-dimensional sensory space.

A matrix of 25 gustatory stimuli combined five sucrose concentrations (0.15 to 2.35 mole/l) with five temperatures (10 to 50 degrees C) or sournesses (pH 1.8 to 5.7). On four different days at the same time of day ten healthy young men served as subjects. Sweet pleasure/displeasure vs. temperature pleasure/displeasure was studied in four subjects and sweet pleasure/displeasure vs. sourness pleasure/displeasure in six subjects. Throughout the first session the 25 stimuli were presented for 5 s each and the subject gave a magnitude estimate of his pleasure or displeasure in response to one dimension of the matrix (e.g. sweetness) regardless of the other. Similarly, throughout the second session, the same stimuli were presented and the subject rated his pleasure or displeasure in response to the second dimension of the matrix (e.g. sourness or temperature) regardless of the first. For the third session however, the subject himself was invited to mix samples, this to allow a behavioural choice in one dimension of the matrix the other being imposed (e.g. he could mix sucrose and water ad libitum for five imposed temperatures). For the last session the subject could adjust the previously imposed dimension, the other previously adjustable dimension being now imposed (e.g. he could modify temperature for five imposed sucrose concentrations). The results of the first two sessions showed that pleasure/displeasure resulted from a two-dimensional combination of the taste modalities offered. The results of the last two sessions showed that the subjects tended to maximize their sensory pleasure. The operant choices coincided with the ratings obtained in the first two sessions. Whether a dimension of the matrix was imposed or operantly adjustable made no difference on the results; the subjects tended to maximize sensory pleasure in the imposed dimension as well as in the adjustable dimension. The subjects therefore maximized their pleasure in the two-dimensional space offered.