1. At least one storage medium having instructions stored thereon for causing a system to perform a method comprising: storing a first user's pupil activity data in the at least one storage medium, the first user's pupil activity data being derived from digital images that were captured by gaze tracker hardware; processing the first user's pupil activity data, using at least one processor, to determine a first attribution of the first user's pupil activity data to first and second elements of a hierarchical user interface (UI) model included on a previously displayed digital first page that displays the first and second elements in a first spatial orientation to one another; processing the first user's pupil activity data, using the at least one processor, to determine a second attribution of the first user's pupil activity data to the first and second elements included on a previously displayed digital second page that displays the first and second elements in a second spatial orientation to one another that is unequal to the first orientation; determining a single aggregate attribution of pupil activity data for one of the first and second elements, but not an additional one of the first and second elements, based on both of the first and second attributions of the first user's pupil activity data; determining an additional single aggregate attribution of pupil activity data for the additional one of the first and second elements based on both of the first and second attributions of the first user's pupil activity data; and attributing first and second portions of the first attribution of the first user's pupil activity data respectively to the first and second elements included on the first page, wherein (a) the first UI model includes a first document object model (DOM) and both of the first and second elements are included in a single hierarchal level of the first DOM, (b) each of the first and second elements has a parent node and a child node; and (c) the first and second portions correspond to a first instance of time.