Under natural conditions, all component qualities of taste mixtures co-exist in space and time on the tongue surface. The significance of space-time coherence of taste sensations was investigated by separating mixture components on the tongue. First, it was shown that a mixture of sucrose plus sodium chloride is judged to have a qualitatively different sweet taste from a mixture of sucrose plus quinine sulphate when all taste qualities are together in space and time. This occurred even though mixtures were matched for sweetness intensity, and the saltiness of the former matched the bitterness of the latter. When, however, mixture components were spatially and temporally separated, the judged quality differences were eliminated. When the components were separated in space only, quality difference judgments were reduced in magnitude, but not eliminated. The results are consistent with the hypothesis that space-time coherence of taste sensations result in perceptual blending and a consequent failure of selective attention to any single component. It is suggested that taste mixtures can be considered as single tastes even though component qualities can be reliably identified using other techniques.