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You probably don’t think you do much with your sense of smell, but your ability to detect odors and to use information about what you smell is pretty remarkable. Your sense of smell provides you with information about the food you are eating, you are in, and the people you are meeting.

Although you can identify positive and negative things from your sense of smell, you also quickly adapt to smells in an environment. You will notice a smell when you first enter an environment, but after a short time, you won’t notice it anymore. It isn’t that the smell has gone away; your brain just doesn’t think it is carrying new information, so you are not aware of it. This process is called habituation.

One thing we know about the ability to perceive things is that you may miss important information if your is focused on something else. In the classic invisible gorilla study, for example, people miss seeing someone walk through a scene in a gorilla costume when they are busy focusing on a ball being passed among people. Perhaps the same thing can happen with smells.

This question was explored in a paper by Sophie Forster and Charles Spence in the October 2018 issue of the journal Psychological Science.

They had participants do an easy or difficult task in a room that smelled of coffee. All participants were able to smell the coffee in the room at the end of the study, so it was clearly detectable.

The easy task involved searching for a target letter on a screen (either an X or an N) and identifying it by pressing a button where everything else on the screen was a small o. The hard task involved searching for the target letter where the other items on the screen were other letters that also have lots of angles (like W, K, H, and Z).

After doing this task for several minutes in the room with the coffee smell, participants were brought to another room and were asked to describe the room as well as they could using all of their senses. About 60 percent of the participants who did the easy task identified the coffee smell, while only 20 percent of the participants who did the hard task could identify it. This was true even when participants were explicitly asked what they smelled in the room.

In a particularly interesting version of this study, participants did the easy or hard task and then described the room while they were still in it. So, they were still in the presence of the coffee smell. Because participants habituated to the smell by the end of the study, only 30 percent of the participants who did the hard task mentioned the coffee smell, while 60 percent of the participants who did the easy task mentioned the coffee smell. After the study, participants were taken from the room for a while and then brought back in, and all of them noticed how strong the coffee smell was.

The results of this last study suggest that being distracted can prevent you from noticing a smell for long enough that your brain habituates to it, and then you are not able to notice it even when you could pay attention to it.

It might seem strange that distraction can keep you from noticing something salient in your environment like smells. However, you live in a world in which there is a constant hum of activity. In order to be able to accomplish your , your brain coordinates your sensory activity to focus on the task you are currently working on. Information that is not related to that task fades to the background. Without this ability to focus your attention, you would have a hard time keeping on track with things you are trying to do.