The influence of olfactory concept on the probability of detecting sub- and peri-threshold components in a mixture of odorants

The headspace of apple juice was analysed to obtain an ecologically relevan t stimulus model mixture of apple volatiles. Two sets of volatiles were mad e up: a set of eight supra-threshold volatiles (MIX) and a set of three sub -threshold volatiles. These sets were used to test the hypothesis that sub- threshold components can change the quality of a familiar smelling mixture of odorants when added to this mixture. In order to test this hypothesis, t hree successive dilutions of the sub-threshold volatiles were prepared in s uch a way that the strongest was at the threshold concentration and the two lower concentrations were below the threshold. The detection probabilities of the sub-threshold components in a blank stimulus were compared with the detectabilities in MIX. The sub- and peri-threshold volatiles were detecte d no better in MIX than in a blank. On the contrary, sub- and peri-threshol d volatiles were better detected alone than when added to MIX. However, whe n the group of subjects was split into two sub-groups, employing either a r ough or a detailed concept definition of the target stimulus, respectively, the subjects with highly refined concepts were better able to detect the p resence of sub-threshold volatiles in MIX than those with poorly refined st imulus concepts. The effect of stimulus concept definition occurred indepen dently of the proportions of correct detections of sub-threshold volatiles in a blank.