A new jsPsych plugin for psychophysics, providing accurate display duration and stimulus onset asynchrony

A JavaScript framework named 'jsPsych' developed by de Leeuw (2015) is widely used for conducting Web-based experiments, and its functionality can be enhanced by using plugins. This article introduces a new jsPsych plugin which enables experimenters to set different onset times for geometric figures, images, sounds, and moving objects, and present them synchronized with the refresh of the display. Moreover, this study evaluated the stimulus onset asynchronies (SOAs) using visual and audio stimuli. The results showed that: (i) the deviations from the intended SOAs between two visual stimuli were less than 10 ms, (ii) the variability across browser-computer combinations was reduced compared with the no-plugin condition, and (iii) the variability of the SOAs between visual and audio stimuli was relatively large (about 50 ms). This study concludes that although the use of audio stimuli is somewhat limited, the new plugin provides experimenters with useful and accurate methods for conducting psychophysical experiments online. The latest version of the plugin can be downloaded freely from https://jspsychophysics.hes.kyushu-u.ac.jp under the MIT license.