Overall, the spider monkeys were relatively sensitive to the six aromatic aldehydes tested in my study. Some of the odorants, bourgeonal and 3-PPA, are among the scents for which spider monkeys have a high sensitivity for, while helional and canthoxal end up among the odorants for which they have a low sensitivity, if compared to other odorant classes tested.

Changes in the molecular structure of the odorant molecules are the only explanation to the differences in sensitivity (as long as the test is done correctly). Bourgeonal and 3-PPA lack the extra methyl group next to the aldehyde group, and were the two odorants with the lowest thresholds. The presence of a methyl group in the structure of an odorant has been found to have an effect on threshold values in previous studies performed in other non human primate species. When comparing the thresholds for indol and 3-methyl indol both squirrel monkeys (Saimiri sciureus) and pigtail macaques (Macaca nemestrina) had considerably lower threshold values for indol compared to 3-methyl indol which contains a methyl group, the same pattern as found in the present study. For pyrazines, the threshold value for spider monkeys decreased systematically with added methyl groups.

Among the aromatic aldehydes the presence of an oxygen-containing methoxy or dioxo groupin the structure appears to lead to an increase in threshold compared to the other odorants lacking such a functional group. Helional and canthoxal were the two odorants for which the animals performed clearly poorer compared to the other stimuli. Helional has a dioxo group, and canthoxal has a methoxy group attached to the benzene ring.

When comparing threshold levels of the odorants with tertiary butyl groups or isopropyl groups it appears that these structural features have a lesser impact on detection threshold for the spider monkeys. The structures of lilial and cyclamal are very similar and differ only from each other in the presence of a tertiary butyl group and an isopropyl group, respectively. The two stimuli were found to have almost identical threshold values. The values are higher than those for bourgeonal and 3-PPA, but lower than the thresholds for helional and canthoxal.