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Psychophysics Toolbox Version 3 (PTB-3) is a free set of MATLAB and GNU Octave functions for vision research. It synthesizes and shows accurately controlled visual and auditory stimuli and interacts with the observer. It has at least twelve thousand active users, an active forum, and is highly cited. PTB-3 is based on the Psychophysics Toolbox Version 2 (PTB-2) but its MATLAB extensions (in C) were rewritten to be more modular and use OpenGL. Psychtoolbox is offered alongside many alternative toolboxes for programming Psychophysics and Psychology experiments, such as PsychJava for Java, or PsychoPy for Python.
Psychophysics Toolbox Version 3 is released under the GNU GPL version 3.