This paper reports on a study which compared two tools for tracking the focus of visual attention - a remote eye tracker and the Restricted Focus Viewer (RFV). The RFV tool blurs the stimuli in order to simulate human vision; the user controls the portion of the screen which is in focus with a computer mouse. Both tools were used by eighteen participants debugging three Java programs for ten minutes each. The results in terms of debugging accuracy and debugging behavior were compared using the restricting view condition of the RFV and a measuring tool as factors. The results show that while the debugging performance and the distribution of the time spent on areas of interest (AOI) are not influenced by the restricting view condition, the dynamics of programming behavior is different. The number of switches between the AOIs as measured by the RFV significantly differed from those measured by the eye tracker. Also the number of switches under the restricted and unrestricted RFV conditio...