Perception of odour intensity and pleasantness. a-b, 66 odours at two concentrations are ordered according to how intense (a) or how pleasant (b) they are perceived to be by the subject population. Odour names are labelled according to odour concentration: grey: low; black: high. Histograms are shown to allow the evaluation of variability. The inset shows the legend for the histograms. The blue lines show statistically significant correlations between the perceived intensity and pleasantness of a given stimulus.