- inattentional blindness (the tendency to miss or actively discard elements in our visual field, demonstrated in the video last month); and
- change blindness (the tendency to fail to notice changes in our visual field).
In last month’s newsletter, I talked about attention and (hopefully) proved that attention is limited to a single mental process. When we attend to something, we have to ignore or discard other things in our visual field that are not relevant to what we are trying to do. The more the task requires our attention, the more we ignore or discard. If you missed last month’s newsletter, check out this video demonstrating this effect. There is a second dimension of attention that designers need to be aware of, and that is how narrow our attentional focus is. Our field of vision associated with conscious attention is limited to something about the size of the tip of your finger. Take a look at the top of one of Escher’s famous drawings of a never-ending staircase (below). As you look across the image you know something is wrong, but you know this from memory. You can’t actually “see” the contradiction in the picture. Cases of this contradiction are too far apart to see at one time. The inability to attend to everything going on and the narrow focus of our attention lead to two related phenomenon, both of which affect interface design: