Characterizing Latency in Touch and Button-Equipped Interactive Systems

International audienceWe present a low cost method to measure and characterize the end-to-end latency when using a touch system (tap la-tency) or an input device equipped with a physical button. Our method relies on a vibration sensor attached to a finger and a photo-diode to detect the screen response. Both are connected to a micro-controller connected to a host computer using a low-latency USB communication protocol in order to combine software and hardware probes to help determine where the latency comes from. We present the operating principle of our method before investigating the main sources of latency in several systems. We show that most of the latency originates from the display side. Our method can help application designers characterize and troubleshoot latency on a wide range of interactive systems

Next-Point Prediction Metrics for Perceived Spatial Errors

International audienceTouch screens have a delay between user input and corresponding visual interface feedback, called input “latency” (or “lag”). Visual latency is more noticeable during continuous input actions like dragging, so methods to display feedback based on the most likely path for the next few input points have been described in research papers and patents. Designing these “next-point prediction” methods is challenging, and there have been no standard metrics to compare different approaches. We introduce metrics to quantify the probability of 7 spatial error “side-effects” caused by next-point prediction methods. Types of side-effects are derived using a thematic analysis of comments gathered in a 12 participants study covering drawing, dragging, and panning tasks using 5 state-of- the-art next-point predictors. Using experiment logs of actual and predicted input points, we develop quantitative metrics that correlate positively with the frequency of perceived side-effects. These metrics enable practitioners to compare next- point predictors using only input logs

A Predictive Approach for an End-to-End Touch-Latency Measurement

International audienceWith direct-touch interaction, users are sensitive to very low levels of latency, in the order of a few milliseconds. Assessing the end-to-end latency of a system is thus becoming an important part of touch-devices evaluation, and this must be precise and accurate. However, current latency estimation techniques are either imprecise, or they require complex setups involving external devices such as high-speed cameras.In this paper, we introduce and evaluate a novel method that does not require any external equipment and can be implemented with minimal efforts. The method is based on short-term prediction of the finger movement. The latency estimation is obtained on the basis of user calibration of the prediction to fully compensate the lag. In a user study, we show that the technique is more precise than a similar "low overhead'' approach that was recently presented