Abstract
Running studies online has become increasingly popular but, for visual psychophysics, it presents some particular challenges due to the high precision that is often required in those studies. For many vision science studies the screen must have a linear luminance profile, rather than one following a gamma function as typically found on computer screens. This presents two problems for online studies. In the lab we would a) measure the luminance profile with a photometer and b) set the gamma value in the graphics card’s Look-Up Table (LUT). In web-based experiments, the browser doesn’t have access to the graphics card LUT and the participant doesn’t typically have access to a photometer. Here, we show how PsychoJS can solve the lack of access to the LUT by controlling the gamma of a browser window using WebGL shaders. We also demonstrate a psychophysical method to measure the screen gamma that is very precise and quick to run (with roughly 30 rapid trials) at the start of a study. With these problems solved many more vision science studies become amenable to experimentation online.