Abstract
Graphical User Interfaces (GUIs) of low visual complexity tend to have higher aesthetics, usability and accessibility, and result in higher user satisfaction. Despite a few authors recently used or studied visual complexity, the concept of visual complexity still needs to be better defined for the use in HCI research and GUI design, with its underlying aspects systematized and operationalized, and different measures validated. This paper reviews the aspects of GUI visual complexity and operationalizes four aspects with nine computation-based measures in total. Two user studies validated the measures on two types of stimuli - webpages (study 1, n = 55) and book pages (study 2, n = 150) - with two user groups, dyslexics (people with reading difficulties) and typical readers. The same complexity aspects could be expected to determine complexity perception for both GUI types, whereas different complexity aspects could be expected to determine complexity perception for dyslexics, relative to typical readers. However, the studies showed little to no difference between dyslexics and average readers, whereas web pages did differ from book pages in what aspects made them seem complex. It was not the intergroup differences, but the stimulus type that defined criteria to judge visual complexity. Future research and visual design could rely on the visual complexity aspects outlined in this paper.