Humans can discriminate trillions of olfactory stimuli, or more, or fewer

TL;DR

This paper critically examines a previous claim that humans can discriminate over a trillion olfactory stimuli, demonstrating that the original estimate was based on a fragile framework that can produce arbitrary results, thus invalidating the claim.

Contribution

The paper exposes the fragility of the estimation method used in the original study, challenging the validity of the trillion-stimuli discrimination claim.

Findings

The estimation framework is highly sensitive to assumptions.

The original claim lacks robust evidence.

Alternative estimates can vary widely based on the method.

Abstract

A recent Science paper (Bushdid et al, 2014)[1] proposed that humans can discriminate between at least a trillion olfactory stimuli. 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 [1]. We conclude that there is no evidence for the original claim.