Motivation
While much basic research exists on the effects of various visual properties on visual search, the application of such research to real-world tasks is lacking. At a CHI 2003 panel, "Research-Based Web Guidelines: Do They Make Better Websites?", the authors of usability.gov noted a lack of empirical validation for web usability guidelines.

The purpose of the following research is to address the lack of empirical validation for design guidelines and practices that affect visual search. In line with this goal are two additional goals: 1) Further inform the development of a predictive tool for evaluation of visual layouts; and 2) Contribute to the theories of applied visual search in human-computer interaction.

Research Questions
Two common "tools" used in web interface design are text color and local density. Text color is often used to differentiate hypertext links from normal text, and also to differentiate visited from unvisited hypertext links. Local density, the number of items per degree of visual angle within a visually distinct group, is often used to distinguish more important from less important information.

The general research question we are asking is, how do text color and local density affect visual search? Specifically we are asking:

With text color
• Does search time increase only as a function of target-colored (e.g. unvisited link) words?
• Do non-target-colored (e.g. visited link) words affect search time?

With local density
• How does the local density affect search time?
• How does the local density affect search strategy?

Research Results
The effects of text color and local density were examined in two separate experiments. The experimental paradigm used to investigate the effects of local density and text color was a two-dimensional menu of words.

The basic findings of the text color experiment are:
• Search time increases as a function of target-colored words.
• However, the presence of non-target-colored words slows search. This effect is greater when the ratio of target-colored to non-target colored words is lower.

The basic findings for the local density experiment are:
• Less time is spent searching per word in sparse layouts.
• People tend to search sparse groups before dense groups.

For a complete discussion of this study, see Tim Halverson's Directed Research Project paper (750KB PDF).