Ok, so, moving on from last week's lecture on modern understandings of human hearing, this week we're talking about olfaction, or the sense of smell. For decades, scientists have believed that smell was a fairly unimportant source of information for us in comparison with other of our five senses. They thought that the human capability for detecting and identifying smells was pretty poor—certainly nowhere near as sophisticated as our animal ancestors. In most circumstances, we rely on our eyes and ears to provide us with knowledge about our surroundings. But, the human capacity for smell is actually very powerful. A 2014 study demonstrated that people can distinguish between over one trillion different smells, but we don't have the language to describe such subtle differences in odour. Plus, a lot of smelling takes place on a subconscious level. Unlike with hearing or vision, for instance, olfactory information from our nasal receptors is not passed directly to the part of our brain associated with consciousness. Instead, it is routed through parts of the brain responsible for emotions and memories. So, we may feel a reaction triggered by a smell before we're even aware that we've smelled anything. Now that biologists understand that the sense of smell operates differently from the other senses, they believe that human sensitivity to smell may be on a par with most other animals.