Understand human olfactory ecology and the methodological challenges in field-testing olfactory ability

We know little about human olfactory ability in natural settings. For humans, this includes both natural and built environments. Our knowledge derives from clinics and lab experiments using samples of convenience, often students and usually WEIRD. But, humans live in odor rich environments, most are not western, and many are not industrialized or formally educated. The problem is that we lack field methods for studying olfactory ability outside the lab and cannot fully understand olfaction within an ecological setting. To explore what clinical methods might be transferrable from the lab to the field, we completed three experiments in a variety of settings with and without repeated measures. Odor purity and background odors at test sites are not mitigated because the larger research question of interest is to understand the impact of varying test environments on olfactory ability, or how our sense of smell operates in daily life. Results suggest that olfactory ability is much worse in non-lab settings than in the lab and that variation in testing due to the environment does not cause significantly different outcomes. Further, we find the that forced choice method for the short odor identification tests introduces a learning bias wherein participants tend to get better at naming odors in the first trial due to having seen correct answers on the forced choice list. Challenges of studying human olfaction in non-lab settings include recruiting participants, minimizing test time, and avoiding subject learning. We report two broader implications of this research. First, comparing field-collected to lab-collected data is not meaningful for understanding human olfactory ecology. The fundamental differences in test conditions (pure single odors in an air-controlled lab versus odor mixtures with variable environmental conditions) preclude robust comparisons. While clinical diagnoses are essential to, in particular, geriatric health, they cannot inform an understanding olfactory performance in an evolutionarily salient way. Second, superior female olfactory ability appeared to be upheld in our field-based studies and we postulate that perhaps there is evolutionary explanation given that females produce most of the food in foraging societies and engage in human-environment interactions in such a way that forces them to learn odors rapidly. These data are the first to explore methods issues on testing olfactory ability in the field in an anthropologically and evolutionarily meaningful way.