User`s guide

E-Prime User’s Guide
Chapter 3: Critical Timing
Page 86
Lets review the example above in detail and assume a 50ms PreRelease time is specified. In the
example, the preparation or setup time was 30ms. So, after 30ms the first stimulus was
presented to the subject. When PreRelease is used, the second stimulus is selected and
prepared for presentation while the first stimulus is still being presented. By 60ms, the second
stimulus is prepared. The program then waits the remainder of the specified duration for the first
stimulus (100ms from the onset of the first display at 30ms), and then presents the second
stimulus (at time 130ms). At this time, the third stimulus is prepared while the second stimulus is
being displayed. All the stimuli would then occur with the intended 100ms interval. The displays
would occur starting at 30, 130, 230, 330ms, etc. From the subject’s point of view, the
experiment would present a stimulus every 100ms with no apparent setup time or cumulative
timing drift.
Figure 7 shows a diagrammatic representation of the timing with and without a PreRelease time
specified. With PreRelease, as long as the preparation time is less than the display time, there
will be no added delays.
Figure 7. Timing diagram of sequential stimulus displays contrasting the use of PreRelease with no PreRelease.
In E-Prime, the stimulus presentation and response processing occur in parallel. This means that
although the next stimulus may be prepared while the current stimulus is still being presented,
any responses entered prior to the actual display of the second stimulus will be scored according
to the settings of the current stimulus (i.e., the response is always scored by the stimulus
prompting the response).
It should be noted that the technique of managing PreRelease also substantially corrects for
Problem 2 (Actual durations can be significantly longer than, and deviate from the intended
durations specified, section 3.2.2). Recall that Windows can arbitrarily halt the program for
periods of tens and sometimes hundreds of milliseconds. If one of these operating system delays
occurs during the critical sequence of “terminate the last stimulus, generate the next stimulus,
and present the next stimulus,” it could potentially produce delays in what the subject sees.
When PreRelease is used, E-Prime accomplishes as much work as possible, as early as possible
(i.e., in some cases as soon as the first object performs its critical action, time can be released to
the next object). It also prepares the display information in an off-screen bitmap so it is ready to