Privacy-Aware Eye Tracking Using Differential Privacy (MPIIDPEye)

Data Collection

Given the lack of a suitable dataset for evaluating privacy- preserving eye tracking using di erential privacy, we recorded our own dataset. As a utility task, we opted to detect different document types the users’ read, similar to a reading assistant [Kunze et al. 2013b]. Instead of printed documents, participants read in VR, wearing a corresponding headset. The recording of a single participant consists of three separate recording sessions, in which a participant reads one out of three different documents: comic, online newspaper, and textbook. All documents include a varying rate of text and images. Each of these documents was about a 10 minute read, depending on a user’s reading skill (about 30 minutes in total).

Participants. We recruited 20 participants (10 male, 10 female) aged 21 to 45 years through university mailing lists and adverts in di erent university buildings on campus. Most participants were BSc and MSc students from a large range of subjects (e.g. language science, psychology, business administration, computer science) and di erent countries (e.g. India, Pakistan, Germany, Italy). All par- ticipants had no, or only minor experience, with eye tracking studies and had normal or corrected-to-normal vision (contact lenses).

Apparatus. The recording system consisted of a desktop com- puter running Windows 10, a 24" computer screen, and an Oculus DK2 virtual reality headset connected to the computer via USB. We fitted the headset with a Pupil eye tracking add-on [Kassner et al. 2014] that provides state-of-the-art eye tracking capabilities. To have more flexibility in the applications used by the participants in the study, we opted for the Oculus ''Virtual Desktop'' that shows arbitrary application windows in the virtual environment. To record a user’s eye movement data, we used the capture software provided by Pupil. We recorded a separate video from each eye and each document. Participants used the mouse to start and stop the document interaction and were free to read the documents in arbitrary order. We encouraged participants to read at their usual speed and did not tell them what exactly we were measuring.

Recording Procedure. After arriving at the lab, participants were given time to familiarise themselves with the VR system. We showed each participant how to behave in the VR environment, given that most of them had never worn a VR headset before. We did not calibrate the eye tracker but only analysed users’ eye movements from the eye videos post hoc. This was to not make participants feel observed and to be able to record natural eye movement behaviour. Before starting the actual recording, we asked participants to sign a consent form. Participants then started to interact with the VR interface in which they were asked to read three documents  oating in front of them. After finishing reading a document, the experimental assistant stopped and saved the recording and asked participants questions on their current level of fatigue, whether they liked and understood the document, and whether they found the document difficult using a 5-point Likert scale (1: Strongly disagree to 5: Strongly agree). Participants were further asked  ve questions about each document to measure their text understanding. The VR headset was kept on throughout the recording.
After the recording, we asked participants to complete a questionnaire on demographics and any vision impairments. We also assessed their Big Five personality traits [John and Srivastava 1999] using established questionnaires from psychology. In this work we only use the given ground truth information of a user’s gender from all collected (private) information, the document type, and IDs we assigned to each participant, respectively.