A considerable amount of effort in HCI (Human Computer Interaction) has been directed to make the user experience more seamless, natural, and integrated into our physical lives. When designing user interfaces, we aim to create tools that will enable the user to accomplish certain tasks with minimum effort, time and difficulty. When evaluating these tools, we take into account individuals' perception of the system such as utility, ease of use and efficiency. However, we tend to consider the user as a conscious thinking mind. In reality, most of our perception of the environment and our behavior is unconscious and does not involve deliberate rational thinking.
We perceive the world indirectly by processing and interpreting the raw data from our senses and our thoughts and behavior are frequently biased by our senses. Among the so-called "five senses," olfactory perception takes an exceptional position in the neurological processing of sensory stimuli.
The olfactory bulb has direct connections to the two brain areas that control emotions and memories: the amygdala and hippocampus. Interestingly the sense of sound, sight, and touch do not pass through these brain areas, they are routed through the thalamus which is the reason why sound, sight and touch interrupt sleep. This makes smell an especially interesting modality to use in human-machine interaction during sleep as well as wake states because it is processed by the brain but does not disrupt the ongoing brain processes as easily.