Inquisit Timing Accuracy
The biggest challenge facing Windows experimentation software is providing reliable,
accurate timing data. The problem is that Windows is not a real time operating system,
meaning that it may introduce anomalies into stimulus presentation times and response
latency measurement. For example, an experiment might present an very large number
of large images on a single trial, the combination of which exceeds display memory
capacity. Or, a high priority system thread may steal CPU cycles from Inquisit while
it is measuring response time.
To be sure, the experimenter can minimize the chances of anamolies by making
sure the system has enough display memory and by shutting down other applications
while running Inquisit. Furthermore, Inquisit can minimize the chance that other
programs, including Windows itself, will steal CPU cycles from it by setting its
process and threads to the highest priority level.
The bottom line is that no software package can guarantee accurate timing
every time. However, a well designed application can take steps that make
timing anomalies very
rare. Inquisit has been developing and tuning its design since 1995 when Microsoft
introduced DirectX for Windows 95 in order to provide reliable, millisecond-accuracy
timing on Windows.
High Performance Design
- DirectDraw for rapid, frame-rate presentation of visual stimuli.
- DirectSound for rapid presentation of sound.
- DirectInput for rapid detection of keyboard input.
- Use of high-peformance microsecond-precision counter to measure response times.
- Support for serial response box devices (e.g., Cedrus and )
to minimize response device latencies.
Built in auditing capabilities to identify timing anomalies.
Independently Tested and Verified
De Clercq, Crombez, Buysse, & Roeyers (University of Ghent, Belgium) have
conducted an independent audit of Inquisit using FASTLOG, a new program they developed
for testing timing accuracy of PC experimentation software. Their results confirm
that Inquisit provides millisecond accuracy stimulus presentation and response timing.
To read a summary of their results,
click here. The full report was published in the following article:
De Clercq, Crombez, Buysse, and Roeyers (2003). A simple and sensitive method to
measure timing accuracy. Behavior Research Methods, Instruments and Computers