Regarding the sense of smell, two different measures of sensitivity can be distinguished: a detection threshold, defined as the lowest concentration at which an odorant can be detected or discriminated from a blank stimulus, and a recognition threshold, defined as the lowest concentration at which an odorant can be assigned a recognizable quality or discriminated from another odorant. It is generally agreed that the detection threshold is lower than the recognition threshold

However, only few studies so far have investigated the magnitude of the difference in concentration between the detection threshold and the recognition threshold in odorants. Furthermore, only few studies have systematically evaluated the impact of stimulus concentration on odorant recognition at the behavioral level. This is surprising given the obvious importance of stimulus intensity for neural coding and for our understanding of the mechanisms underlying recognition and discrimination of odorants. For this reason, the present study aimed at determining olfactory detection thresholds for five members of a homologous series of aliphatic aldehydes, in a group of human subjects, and testing the ability of the same subjects to discriminate between the same odorants when presented at different concentrations above their individual detection thresholds.