As technology develops, the prevalence of conventional book dictionaries has slowly declined due to advancements in computer-mediated aids, such as online type-in dictionaries and program-installed pop-up aids. The goal of this study was to examine how technology "may" have changed the long-standing pedagogical practice of book dictionary usage by identifying the learning processes associated with various dictionaries and verifying how these processes are related to learning. Cognitive load theory was applied to generate predictions about learning performance and, therefore, to determine the nature of these processes. Information contained in each dictionary was specifically controlled, and thus we focused on the effect of the learning process alone. In the experiment, students first read a simulated online text in one of four conditions: pop-up, type-in, book dictionaries or no aid. They were later tested for reading comprehension and vocabulary learning. Results indicated that all dictionaries enhanced vocabulary learning but not comprehension. Close examination revealed that vocabulary-learning efficiency was significantly higher for the pop-up dictionary than the other two aids. In addition, a complex relationship existed between reading comprehension and vocabulary learning. This study has important implications for future dictionary design and pedagogical advice regarding dictionary usage. (C) 2010 Elsevier Ltd. All rights reserved.