We propose a Bayesian model for extracting sleep patterns from smartphone events. Our method is able to identify individuals’ daily sleep periods and their evolution over time, and provides an estimation of the probability of sleep and wake transitions. The model is fitted to more than 400 participants from two different datasets, and we verify the results against ground truth from dedicated armband sleep trackers. We show that the model is able to produce reliable sleep estimates with an accuracy of 0.89, both at the individual and at the collective level. Moreover the Bayesian model is able to quantify uncertainty and encode prior knowledge about sleep patterns. Compared with existing smartphone-based systems, our method requires only screen on/off events, and is therefore much less intrusive in terms of privacy and more battery-efficient.

Gaze and head tracking, or pointing, in head-mounted displays enables new input modalities for point-select tasks. We conducted a Fitts' law experiment with 41 subjects comparing head pointing and gaze pointing using a 300 ms dwell (n = 22) or click (n = 19) activation, with mouse input providing a baseline for both conditions. Gaze and head pointing were equally fast but slower than the mouse; dwell activation was faster than click activation. Throughput was highest for the mouse (3.24 bits/s), followed by head pointing (2.47 bits/s) and gaze pointing (2.13 bits/s). Dwell activation was faster than click activation. The effective target width for gaze (≈ 94 pixels; about 3 •) was larger than for head and mouse (≈ 72 pixels; about 2.5 •). Subjective feedback rated the physical workload less for gaze pointing than head pointing.

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Lab's binocular gaze tracking unit (used for gaze input). The Fitts' multi-directional selection task that the participant is performing inside the headset is also shown on the monitor. The headset also tracks orientation of the head (used for head input). B. Feet on a 3DRudder foot mouse with 360 • of movement control (used for foot input). Tilting the 3DRudder moves the cursor in that direction.

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