A new paper is questioning the results of a study published last year, which suggested that the human nose can distinguish at least 1 trillion odors.
Rick Gerkin, from the Arizona State University School of Life Sciences, and colleague Jason Castro, also from the Arizona State University, argue that the data that were used in the study do not support the claim.
Gerkin said that the findings of researchers from the Howard Hughes Medical Institute and The Rockefeller University, which were published in the journal Science last year, now make their way to neuroscience books, and this could have unwanted impact on studies that do not agree with those findings and which could misinform upcoming investigators.
Gerkin and Castro showed in their study, which was published in the journal eLife on July 7, that if the experiments conducted for the study used about 100 additional subjects, the same analysis may have likely suggested that the human nose is able to differentiate all possible odors, which does not agree with the data in the research.
"Here we show that this claim is the result of a fragile estimation framework capable of producing nearly any result from the reported data, including values tens of orders of magnitude larger or smaller than the one originally reported in (Bushdid et al., 2014)," the researchers wrote.
Gerkin and Castro also said that had the research involved a more conservative statistical analysis, the study would have revealed that humans can only distinguish 5,000 odors.
"The assertion that humans can discriminate between at least 1 trillion odors is based on a fragile mathematical framework—one that's capable of creating nearly any result with small variations in the data or the experiment design," Gerkin said.
The researchers said that the number of smells that can be distinguished by humans is something that could come when olfaction is better understood, which is currently lacking. They added that this should be established in order to have a better understanding of olfactory health and smell diseases.
Gerkin said that scientists are able to compute the number of distinguishable colors because they are aware of how color perception is organized, but smells do not have a "smell wheel" yet. The researcher said that scientists still have to discover the organization of olfactory perception to be able to know how many unique smells there are.
Photo: Dennis Wong | Flickr
