Contextual effects in the perception of quinine HCl/NaCl mixtures.

Stimulus distribution, stimulus spacing and stimulus range affect mean intensity ratings of solutions of unmixed tastants. The present study compares contextual effects for mixture ratings with those for unmixed stimuli: if ratings for mixed and unmixed stimuli are differentially affected by context, the degree of mixture suppression inferred from the responses is context-dependent. Bitterness intensity ratings for unmixed quinine and quinine HCl/NaCl mixtures were not differentially affected by shifts in stimulus frequency distribution. The subjects' tendency to be consistent in their responses to identical stimuli, results in a transfer of stimulus context of previous sessions to the next.