When we are designing user interfaces it’s important to be aware of where the users locus of attention are, so that we are able to show crucial information where the user has his or her attention.
The term was coined by the late Jef Raskin who were one of the pioneers of designing the first Macintosh. He is sometimes actually referred to as “The father of Macintosh”.
“I use the term locus because it means place, or site. The term focus, which is sometimes used in a similar connection, can be read as a verb; thus , it conveys a misimpression of how attention works.”
The Humane Interface – Jef Raskin, 2000
Real world example
One way to implement this concept is to allow input where there is output. The edit-in-place design pattern, as for example seen on Flickr, where you can edit a heading by just clicking on it, is a perfect example of this.
1. You want to change the title of a photo so you click where you have your locus of attention: The title.
2. The title becomes editable and you enter a new title.
3. When you click the Save button a message telling you that the title is being saved appears right where your locus of attention are.
4. And just like magic the new title appears.