Figure

Overlapping transparent letters of the type used by Vecera and Farah (1997).

way of clarifying the notion of simplicity. He studied the ways in which dots moving across a display are perceived. The most complicated approach would be to treat each dot as completely separate from all the others, and to calculate its starting position, speed, and direction of movement, and so on. In contrast, it is possible to treat the moving dots as belonging to groups, especially if they move together in the same direction and at the same speed. Restle was able to calculate precisely how much processing would be involved. Whatever grouping of moving dots in a display involved the least calculation generally corresponded to what was actually perceived.

Julesz (1975) pointed out that most of the stimuli used by the Gestaltists and their followers were very limited in that they were based mainly on lines and shapes. He studied the effects of brightness and colour on perceptual organisation. A visual display was perceived as consisting of two regions if the average brightness in each region differed considerably. However, a display was not perceived as divided into two regions if the detailed pattern of brightnesses in each region was different but there was only a modest difference in the average brightness. In similar fashion, a visual display consisting of coloured squares is perceived as forming two regions if the average wavelength of light in each region is clearly different. Two regions are less likely to be perceived if there are different patterns of colours in each region, but the average wavelength differs only slightly (e.g., mostly red and green squares in one region, and mostly yellow and blue squares in the other region).

Julesz (1975) found that there are some exceptions to the notion that average brightness or wavelength is crucial in determining whether a display is perceived as consisting of two regions. Another important factor is granularity, which refers to the way in which the elements in a region are distributed. At one extreme, all the elements could be evenly distributed within the field; at the other extreme, they could all be clumped together. Julesz found that a display in which the overall brightness is the same throughout the display but the granularity is greater in one half than the other will be perceived as consisting of two regions (see Figure 2.4).

The Gestaltists de-emphasised the complexities involved when laws of grouping are in conflict. This issue was addressed by Quinlan and Wilton (1998). For example, they presented a display such as the one

Business Correspondence

Business Correspondence

24 chapters on preparing to write the letter and finding the proper viewpoint how to open the letter, present the proposition convincingly, make an effective close how to acquire a forceful style and inject originality how to adapt selling appeal to different prospects and get orders by letter proved principles and practical schemes illustrated by extracts from 217 actual letter.

Get My Free Ebook


Post a comment