Analysis of Odour Similarities from Electrophysiological Data

The activity of single units in the olfactory bulb of the frog was recorded extracellularly by means‐of microelectrodes. The electro‐olfactogram was recorded simultaneously from the olfactory epithelium. The sensory epithelium was stimulated with substances selected from a recent classification of odorous compounds to represent five of the stereochemical groups of Amoore. The effect on a bulbar unit was classified as excitatory or inhibitory. The chi‐square values and the corresponding probability values were calculated for all pairs in a given series. The statistical values were regarded to represent measurements of relatedness in olfactory stimulative properties between the tested substances. For each series the data were analysed with a nonmetric multidimensional scaling method to give spatial representations of the relatedness between the odours. The relation of the results to psychophysical findings and the classification of odours according to the stereochemical theory are discussed.