User`s guide

E-Prime User’s Guide
Appendix A: Timing Test Results
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Windows desktop computers can support millisecond precision timing if they are
reasonably configured. It is prudent to run the time test programs whenever new
hardware or applications are added to the computer. The timing test results in this section
show that E-Prime can maintain millisecond precision on appropriately tuned desktop PC
hardware for Pentium class machines running at 120MHz or faster. Experiments can take
precision real-time input from the keyboard device or PST Serial Response Box, but we do
not recommend that the mouse be used as an input device for experiments in which
response time at the millisecond level is the primary dependent measure. Using a quality
name brand PCI audio card, E-Prime can achieve consistent low latency playback of digital
audio (e.g., latency < 1 screen refresh). We do not recommend using a legacy ISA audio
card for experiments that require optimal and consistent playback latency. Please refer to
the timing test summary data at the end of this section for a detailed review of the tests
performed and the resulting data.
Applications frequently install either new background jobs that take processor cycles or new
device drivers that may alter timing precision. Some hardware cards and software programs
compromise the machine’s ability to provide millisecond precision. The testing of the computer
needs to be done when the computer is initially setup or when new hardware or software is
installed, but it need not be done for every experiment. The rest of this section details how the
testing should be performed. If the system has already passed the performance tests described
and someone else is responsible for machine configuration testing, then this section may be
skimmed, although the figures should be reviewed. Once the machine passes the performance
tests, it is ready to serve as a data collection station for E-Prime.
People tend to install multiple background applications that may, at intervals, wake up and steal
cycles from other applications (e.g., the experiment), resulting in timing errors. For example, the
Windows
®
Office toolbar periodically checks the state of the machine to see if some action needs
to be performed (e.g., put up a reminder alarm on the screen). These types of programs use
small amounts of time, but can block or delay other programs from executing and therefore can
result in timing errors. Having multiple applications running encourages the operating system to
swap out parts of the experiment (see Chapter 3-Critical Timing). A common problem is virus
detection programs that scan all files and periodically scan the system for viruses. There is an
internal timer in the virus monitoring applications that will, on some cycle, wake up and scan the
system, halting activity for potentially hundreds of milliseconds. To avoid random time delays
during the experiment, scanning must be disabled while running the experiment. E-Prime runs in
high priority mode and will block most, but not all such background jobs.
A good experimental computer should have a minimum number of concurrent applications
running and no other applications loaded during a data collection run. Ideally, no other
applications other than E-Run should be displayed on the Windows taskbar when real data is
being collected. There should also be a minimum number of background applications and utilities
running (this is typically determined by what programs are on the Start menu configuration for the
computer but can also be affected by various non-obvious entries located in the Windows System
Registry). Pressing Ctrl+Alt+Del will display a list of all programs currently running on a