Precision refers to the trial-to-trial variability of the measures: the jitter of the timing measurement or its “variable error”. In general, precision is the more important issue for a behavioral scientist. Yet there is a lack of information in the literature about what is actually possible to achieve with different packages and operating systems, and very few labs report testing the timing of their studies themselves.īefore going further, we should establish the distinction we draw between accuracy and precision.
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Indeed, we often hear people state that they use particular software packages because they “need sub-millisecond timing”. Many scientists need high-precision timing of stimuli and responses in their behavioral experiments and rely on software packages to provide that precise timing. We stress the importance of scientists making their own timing validation measurements for their own stimuli and computer configuration. The results, from over 110,000 trials, highlight the wide range of timing qualities that can occur even in these dedicated software packages for the task. Nonetheless, the data indicate that online methods can be suitable for a wide range of studies, with due thought about the sources of variability that result. There was considerable variability between OS/browser combinations, especially in audio-visual synchrony which is the least precise aspect of the browser-based experiments. For response times (measured using a high-performance button box), most of the packages achieved precision at least under 10 ms in all browsers, with PsychoPy achieving a precision under 3.5 ms in all. That said, PsychoPy and Gorilla, broadly the best performers, were achieving very close to millisecond precision on several browser/operating system combinations. Online studies did not deliver the same level of precision as lab-based systems, with slightly more variability in all measurements. Across operating systems, the pattern was that precision was generally very slightly better under Ubuntu than Windows, and that macOS was the worst, at least for visual stimuli, for all packages. OpenSesame had slightly less precision across the board, but most notably in audio stimuli and Expyriment had rather poor precision. Among the lab-based experiments, Psychtoolbox, PsychoPy, Presentation and E-Prime provided the best timing, all with mean precision under 1 millisecond across the visual, audio and response measures. Where possible, the packages were tested on Windows, macOS, and Ubuntu, and in a range of browsers for the online studies, to try to identify common patterns in performance. We compared a range of popular packages: PsychoPy, E-Prime®, NBS Presentation®, Psychophysics Toolbox, OpenSesame, Expyriment, Gorilla, jsPsych, Lab.js and Testable. Here we report a wide-ranging study looking at the precision and accuracy of visual and auditory stimulus timing and response times, measured with a Black Box Toolkit. Very little information is available, however, on what timing performance they achieve in practice. There are a large number of software packages with which to conduct these behavioral experiments and measure response times and performance of participants. Many researchers in the behavioral sciences depend on research software that presents stimuli, and records response times, with sub-millisecond precision.
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