What We Can Easily See
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This chapter is about the theory of vision that describes what makes something small easy to see. It is also about the details of design. The most important and frequent visual queries should be supported with the most visually distinct objects. The perceptual laws of visual distinctness are based on the low-level early-stage processing in the visual system. Visual distinctness has as much to do with the visual characteristics of the environment of an object as the characteristics of the object itself. A design to support a rapid visual query for two different kinds of symbols from among many others will be most effective if each kind of query uses a different channel. Making objects move is a method of visibility enhancement that is in a class by itself. Motion is extremely powerful in generating an orienting response. One key to making efficient visual search is through the use of pop-out properties. If a visual object is distinct on one or more of the visual channels, then it can be processed to direct an eye movement. The strongest pop-out differentiators are the basic feature channels found in V1. These include the elements of form, size, elongation, and orientation; the elements of color, including hue and lightness; and motion and spatial layout. If the design being searched conforms to stereotype, then search will be easy because habitual visual scan patterns, guided by spatial structure, will support search. If a design violates a learned pattern, then searches using habitual eye movement strategies will result in frustration.