About back-ends
Overview
About back-ends
The back-end is the software layer that deals with input (keyboard input, mouse input, etc.) and output (display presentation, sound playback, etc.). There are many Python libraries that offer this type of functionality and OpenSesame could, in principle, use any one of them. For this reason, OpenSesame is back-end independent, in the sense that you can choose which back-end should be used. Currently there are five different back-ends: legacy, psycho, droid, xpyriment, and opengl (deprecated).
Differences and some tips
Usually, you won’t notice which back-end is used. The differences between back-ends are largely technical, and, as long as you use the graphical user interface or the openexp Python modules, all back-ends work the same way. However, there are a number of reasons to prefer one back-end over another in a particular situation.
- Not all back-end are equally accurate when it comes to timing.
- Tip: If you care about millisecond precision timing, use
xpyrimentorpsycho.
- Tip: If you care about millisecond precision timing, use
- Not all back-ends are equally fast when it comes to generating stimuli.
- Tip: If forms are slow, use
legacy. - Tip: If the intertrial interval is long (due to stimulus preparation), use
legacy.
- Tip: If forms are slow, use
- You can make use of back-end specific functionality when writing Python inline code.
- Tip: If you want to use PsychoPy functionality, use
psycho. - Tip: If you want to use Expyriment functionality, use
xpyriment. - Tip: If you want to use PyGame functionality, use
legacy.
- Tip: If you want to use PsychoPy functionality, use
- Not all back-ends are supported on all platforms.
Selecting a back-end
The easiest way to select a back-end is using the combobox in the “General tab” of the experiment (Figure 1).
Figure 1. The back-end selection combobox.
If you view the general script (select “Show script editor”), you will see that there are actually five distinct back-ends, for the canvas, keyboard, mouse, sampler and synth. The combobox-method automatically selects an appropriate, pre-defined combination of back-ends, but you could, in theory, mix and match.
For example, if you select the psycho back-end, the following code will be generated:
set mouse_backend "psycho"
set sampler_backend "legacy"
set keyboard_backend "psycho"
set canvas_backend "psycho"
set synth_backend "legacy"
