Computer users who handle complex tasks like air traffic control (ATC) need to quickly detect updated information from multiple displays of graphical user interface. The objectives of this study are to investigate how much computer users can segment GUI display into distinctive objects within very short glances and whether human perceives complexity differently after different durations of exposure. Subjects in this empirical study were presented with 20 screenshots of web pages and software interfaces for different short durations (100ms, 500ms, 1000ms) and were asked to recall the visual objects and rate the complexity of the images. The results indicate that subjects can reliably recall 3-5 objects regardless of image complexity and exposure duration up to 1000ms. This result agrees with the “magic number 4” of visual short-term memory (VSTM). Perceived complexity by subjects is consistent among the different exposure durations, and it is highly correlated with subjects’ rating on the ease to segmentation as well as the image characteristics of density, layout, and color use.