It has been assessed that for a package to halt a customers’ attention on a supermarket shelf, it should do so within one twentieth of a second. Tests also indicate that a black-and-white magazine advertisement may sustain the interest of a reader for al little as two-thirds of a second, whereas a coloured advertisement may hold the attention for perhaps two seconds or more.
With such restricted time-spans to contend with, simplicity of the elements composing a design is generally to be recommended. While the repetition of design components of equal importance may be apt for a wallpaper or textile design, in graphic design and typography it is usually more appropriate to hold in balance dominant against less-dominant visual features. As a general rule, when emphasizing legibility and visual stability, the designer does not want to include a number of design components all ‘fighting’ for the same degree of attention.
While normal object-perception involves emphasizing ‘foreground’ features or objects generally at the expense of those in the ‘background,’ the designer must often develop a facility for assessing and balancing both the ‘figure’ and the ‘ground’ in her/his attention at the same time, before eventually establishing the appropriate emphasis of each.
When selecting colour comparisons for lettering, for example, contrasts of light against dark are preferable to emphasizing differences of colour (hue) or colourfulness (chroma). In other words, lettering is read more quickly and legibly where there are substantial light-dark differences between the colours used for the letting and the background.
Another important factor is the speed with which the designer must impress her/his message on the reader or potential purchaser. One factor is the fast pace of contemporary life, but another is to be found in examining the nature of visual sensing itself.
Though the human eye is able normally to scan a wide area, the part of the visual field which is in focus as any given instant is surprisingly small — about the size of one’s thumbnail viewed at arm’s length. As a consequence, the eye needs to make an enormous number of slight visual shifts (an average of 5 each second) in order to explore the visual world, and convey in-focus visual information back to the brain, where such glimpses are amalgamated into a seamless perception of the so-called outside world.
Though the retina, which lines the interior of each eye, occupies many square millimetres, the portion of it which permits us to see in focus is remarkably small — less than 2 millimetres across. This cavity, known as the central fovea, possesses a dense concentration of visual sensing cells. Hence it is only the very centre of our visual field which sees with greatest sharpness or acuity of vision and which sees also most efficiently in colour.