Analysis of the Drosophila antenna recording. a) Maximum response (after odour stimulation) for response units (y-axis) and a series of odour stimulations (x-axis). All odours were dissolved in (odourless) mineral oil, which was also given multiple times as a control. As a reference, the odours nonanone and heptyl acetate were applied multiple times. Response units are sorted by response to the first nonanone stimulation. Odours are sorted by name. The log colour scale ranges from blue (global min) to red (global max). b) Hierarchical clustering of the odour feature vectors from a) using Ward's method (stats package for R) based on Euclidean distances between the feature vectors. Marked clusters: Odourless substances (grey), hexanoates (purple), heptyl acetate (green), nonanone (blue).