Most computer aided detection (CAD) systems for mammographic mass detection display all suspicious regions identified by computer algorithms and are mainly intended to avoid missing cancers due to perceptual oversights. Considering that interpretation failure is recognized to be a more common cause of missing cancers in screening than perceptual oversights, a dedicated mammographic CAD system has been developed that can be queried interactively for the presence of CAD prompts using a mouse click. To assess the potential benefit of using CAD in an interactive way, an observer study was conducted in which 4 radiologists and 6 non-radiologists evaluated 60 cases with and without CAD, to compare the detection performance of the unaided reader with that of the reader with CAD assistance. 20 cases had a malignant mass, and 40 were cancer-free. During the reading sessions we recorded time and probed locations which reveal information about the search strategy and detection process. The purpose of this study is to determine a relation between detection performance and time to first probe of the lesion and to investigate if longer reading times lead to more reports of malignant lesions in lesion-free areas. On average, 65.0% of the malignant lesions were found within 60 seconds and this percentage stabilizes after this period. Results suggest that longer reading time did not lead to more false positives. 74.6% of the reported true positive findings were hit by the first probe, and 93.2% were hit within 5 probes, which may suggest that many of the correctly reported malignant masses were perceived immediately after image onset.