Effects of Information Density and Size on the Perception of Graphics in User Interfaces

II HELSINKI UNIVERSITY OF TECHNOLOGY ABSTRACT OF MASTER’S THESIS Author: Title of thesis: Date: 10.3.2003 Tomas Lindberg Effects of Information Density and Size on the Perception of Graphics in User Interfaces Number of pages: 69 Department: Professorship: Supervisor: Instructor Computer Science and Engineering Tik-121 User Interfaces and Usability Professor Marko Nieminen Risto Näsänen, Ph.D., Docent Alphanumeric and graphical information needs to be presented in such a way that its perception is accurate, fast and as effortless as possible. This study investigated the effects of spacing and size of individual interface elements on their perception. Experiment 1 investigated the effect of spacing on the speed of perception for elements in groups of varying size and defined the number of icons that can be seen with one glance (that is, with one eye fixation), experiment 2 studied the effect of size and experiment 3 the subjective preferences of people. In experiment 1 three subjects searched for a target icon from among a group of distractors. In the experiment the array size (set size) and inter-element distances were varied. The array sizes were 2x2, 3x3, 5x5, 7x7 and 10x10 icons and the inter-element distances were zero icons, 1⁄4 icon, 1⁄2 icon, one icon and two icons. Eye movements were measured during the experiment. In experiment 2 subjects also searched for an icon (the same as in experiment 1) from a group of distractors. This time the array and inter-element distance were kept constant (10x10 and one icon respectively) with varying viewing distance. Viewing distances used were 28 cm, 57 cm, 114 cm and 228 cm corresponding to icon sizes in degrees of visual angle of 1.48, 0.74, 0.37, and 0.18, respectively. No eye movements were recorded. In experiment 3, fourteen subjects arranged paper printouts of different levels of inter-element spacing of one array size into their preferred order. That is, the one they liked the best was placed first and the one liked the least was placed last. The results of experiment 1 showed that spacing does not have an effect on threshold search times. The perceptual span for icons was found to be 25 in total arranged in a 5x5 array. The size of the interface elements on the other hand was found to have a great effect. Icons smaller than 0.7 degrees of visual angle resulted in significantly raised threshold search times. For both experiments, however, there were differences between subjects. Experiment 3 revealed that an inter-element spacing of one icon is to be preferred and a spacing of zero icons is to be avoided.