Application Programming Interface(API) form an important part of software development. Eye tracking is an interesting and emerging field which is gaining wide popularity. The goal of the thesis is to collect and utilize eye tracking data to better understand how software developers summarize code. We perform a study that measures the effects of complex information sources on summarization tasks. In this work, we conduct a controlled experiment with 12 professional and student software developers to better understand how they perform code summarization tasks. These tasks aimed at summarizing a set of APIs based on source code, Stack Overflow, Bugzilla, or a combination of them. We used iTrace, a plugin for Eclipse, to record the developers' eye movements.