Visual Perception and Its Impact on Technical Communications 
by Susan Kaltenbach

 

Past studies of visual perception have produced a wide library of information on what forms of information can be most easily absorbed by the user.

In this paper, we consolidate the literature to provide guidelines on the most effective steps in text engineering, with applications in both printed documentation and website design.

Type Considerations

In printed documents, efficacy can be improved by the text characteristics. Qualities such as font size, upper or lower case characters, or line length can be engineered to significantly improve the user’s absorption capacity.

In this section, we will discuss some basic components of text and the optimal configurations that current research has discovered. 

Serif versus Sans Serif fonts

Some research demonstrates that using a serif font in print documents is beneficial to users. The serif font speeds the reading process by helping users to distinguish characters more easily. The use of a serif font may also assist in information “chunking,” to make short-term memory use more efficient.

 
Comprehension Level: Serif versus Sans Serif typeface [5]

  

Good

Fair

Poor

Layout with serif body type

67%

19%

14%

Layout with sans serif body type

12%

23%

65%

 

Typeface size

To optimize clarity and reading ease, fonts for printed documents should be within the size range of 11- to 12-point type. Note that special needs audiences may require a larger type size for accessibility.

This is an 8-point font.
This is a 10-point font.

This is a 12-point font.

This is a 14-point font.

Use of Italics

Italics are often used to introduce new concepts, identify foreign phrases, or emphasize a section of the text message. There is no evidence to suggest that italic usage results in less readability.

Bold

Bold type can be effectively used for text emphasis. When the occurrence of bold type becomes too frequent, the reader experiences eye fatigue and comprehension declines.

Capitalization

Wheildon’s findings determined that when text is presented entirely in upper case, readers found it difficult to read. When text is changed to the standard lower case presentation, comprehension increases by over 90%.

TEXT PRESENTED ENTIRELY IN UPPER CASE MAKES A DOCUMENT VERY DIFFICULT TO READ.

When the text is presented in standard lower case, reading comprehension can increase dramatically.

Underlining

Underlining, by spoiling the shape of the letter, makes text difficult to read. There are many other alternatives. Underlining should never be used either in body text or in headlines.

Reversed text

One mechanism often used by graphic designers is the presentation of white text on a black background to add emphasis. While this practice may be appealing from a graphical design viewpoint, reversed text suffers from extremely poor visibility.

Reversed text can also fall victim to extremes in color opposition, resulting in visual fatigue and “false motion” or other optical effects.

Length of a line in the body text

The length of a line can have dramatic effects on the readability of a document in both print and web form. A common metric is to have a sentence length in the range of 1 1/2 to 2 alphabets, approximately 38 to 50 characters per line.

Leading (space between lines)

A line of text which exceeds the optimal length can still have its readability improved by increasing the leading. One suggestion is to apply an additional point of leading for every five (5) characters added to the optimal length. No line length should exceed 65 characters. This is especially important in web site design, where visual fatigue factors are a predominant concern.

White (blank) space

Hard and soft cover books have traditionally been printed with approximately 50 percent blank space. Comprehensibility decreases if 60 percent or more of a page is filled with content.

Justification of body text

In the past, it has been a standard to left-justify text with a ragged right column. However, recent research has demonstrated that a fully-justified right margin improves the comprehensibility of documents.

Implementing a fully justified right margin improves reader tracking and makes the divisions between words clearer.

Research has found that a fully-justified paragraph is more readable than a paragraph with a ragged right margin.

By using a fully-justified right margin, the body text can be accessed by the reader more efficiently.

Comprehension Level based on Justification [5]

Good

Fair

Poor

Layout with totally justified setting

67%

19%

14%

Layout with ragged right setting

38%

22%

40%

Layout with ragged left setting

10%

18%

72%

Section Two: Color Perception

The human eye perceives color through the use of three color receptor nerve cell types called cones. The three cone types are sensitive to different wave lengths (colors) of light. There are slightly more red receptors in the eye than green, while there are very few blue receptors compared to red and green.

Use of the color Blue

Due to the distribution of cones in the human retina, our ability to see blue images is significantly different than our ability to see red and green. The cones that absorb blue light are actually more prevalent in our peripheral vision than our foveal vision. This results in a lessening in our ability to see blue as we focus.

Our lack of blue cones in the foveal region also impacts our ability to focus due to how we detect edges in an image.

Our visual system processes the information detected by the eye in three perceptual channels: luminance, chromanance, and motion. The luminance channel takes input primarily from the red and green cones. The luminance channel enhances the contrast of edges, producing, in effect, a bandpass filter. Since blue cones represent only 5 percent of the cone population in this region, their contribution to luminance perception is significantly less.

Obviously, using the color blue for text produces several perceptual problems. However, printing in dark blue circumvents some of these problems, since the luminosity of that color is lower. This provides more contrast to the background (assuming a reasonable background is used)..

In the eye’s peripheral vision, the ratio of blue cones to red and green is 1 to 14.

In the foveal (high acuity) region of the human retina, the ratio of blue to red/green drops to 1 to 20.

References 

  1. Factors influencing the design and layout of manuals and other published material, http://www.rightwords.co.nz/layout.html#Serif_or2

  2. Craig, James: Basic Typography: A Design Manual Watson-Guptill Publications 1990

  3. Robinson, Les: Making Reader Friendly Publications Working Life Communications 1991

  4. Rollo, Lindsay: Words and images in print and on screen in "SET: Research Information for Teachers" vol 2, item 14, 1993

  5. Ryder, John: The Case for Legibility The Bodley Head 1979

  6. Wheildon, Colin: Type and Layout. How typography and design can get your message across - or get in the way Strathmore Press 1995