This experiment measured the lag between a click event registered on the touch screen monitors in the CES lab and the actual (estimated) moment of contact between finger and screen. It was expected that this latency measure would be highly variable (as mouse/keyboard events often are) and indeed this was the case.
The latency of the touchscreen was measured by clicking a button on an application called ClickMe that outputs an even marker every time the button is clicked. The button was clicked repeatedly by a hand in a PhaseSpace glove and the motion of the index finger LED was recorded. The data was then compared with this code. Below is a sample of the data. The black signal is the magnitude of the LED (the square root of the sum of the squares of each direction measured), the green line is the moment that LSL records the click and the red line is the estimated peak of the magnitude -- presumably this is the moment when the finger touches the screen.
As suspected, the click events were quite noisy with respect to time. This is due in part to how Windows 7 handles HCI events and the hardware of the screen itself. The mean lag time for clicks on the screen was found to be 147.40ms which was quite near the median lag time of 145.12ms. The outliers were many and created a significant spread in the results.
The data for this experiment was taken on 10/27/2014.