1. A method of classifying user activities, comprising: at a computer system having one or more processors and memory: receiving eye tracking data for a person interacting with a computer and visual content using one or more user interface devices, the eye tracking data comprising a sequence of fixations ordered temporally, wherein each respective fixation corresponds to a plurality of respective consecutive measured gaze points, and wherein each respective fixation has a respective duration and location based on the corresponding respective measured gaze points; receiving user interaction data from the one or more user interface devices; and for each fixation in the sequence: determining a plurality of features for the fixation, including one or more characteristics of the fixation and one or more user interaction features based on the received user interaction data; and associating a user activity label with the fixation in accordance with the plurality of features, wherein the user activity label is selected from a predefined set of user activity labels; wherein the fixations are grouped and matched with regions of the visual content according to the locations of the fixations, the user activity label associated with the fixations, and content type of the regions.