The perception of flavor arises from the combination of inputs from several sensory modalities, especially gustation (taste proper) and olfaction (the primary source of flavor qualities). Both the perception of intensity of suprathreshold flavorants and, notably, the detection of weak flavorants are consistent with a rule of additivity. Thus, the detectability, d', of mixtures of the gustatory flavorant sucrose and the olfactory flavorant vanillin approximates the additive sum of detectabilities of the two components, within a model that assumes pooled noise in the flavor system that derives from both modalities. When gustatory and olfactory flavorants are presented in isolation, however, under conditions that encourage or permit selective attention to one modality or the other, it may be possible to filter out the noise associated with the unattended modality, and leading thereby to a rule of vector summation.