An odor like Brewing coffee is easily noticed

Some student nurses are at a party. Because they love anatomy so much, they make the following observation: a When entering a room, an odor like brewing coffee is easily noticed. A few minutes later, the odor may

be barely, if at all detectable, no matter how hard one tries to smell it.
In a noisy room, nurses are able to engage in a conversation while ignoring the background noise. The
background noise is not noticed until a conscious effort is made to hear it.
Explain the basis for each one of these observations.