Mode

Synchronization mode:

0 immediate rendering

1 synchronization of visual and auditory presentation with screen refresh

By default, all visual commands render immediately to the graphics card not considering synchronization with the visual refresh cycle of the monitor. If synchronization is turned on, all visual and auditory commands will be queued and rendered at the beginning of the next available animation frame. The image will be visible starting with the next screen refresh. So, the total time delay is between 1 and 2 refresh periods.

The benefit of synchronizing stimulus presentation with the refresh cycle of the monitor is that the measurement of reaction times will be auto-corrected to reflect the estimated onset of the visual image. This reduces the variance of reaction times by subtracting the random gap between trial event and screen refresh and increases the absolute accuracy by subtracting one visual frame period to reflect the delay between internal rendering to actual presentation on the screen.

This synchronization is based on a standard browser API (rAF) designed for aligning visual presentation with the screen refresh of monitors. The exact behavior depends on the browser model and graphics card.