User`s guide

E-Prime User’s Guide
Chapter 3: Critical Timing
Page 88
Log Post Response
Log Before Response
Figure 8. Interaction of extended response interval. In Log Post Response (above), data from response has
been collected before recording for logging (shown as “”$”). In Log Before Response, the logging occurs before
the extended response interval is completed and hence response events may not be recorded.
A second caveat when using PreRelease is that the PreRelease mechanism can only be used
effectively if the current stimulus object is not being cleared at the end of its Duration. This is
because an object responsible for its own clearing must always wait its full, specified Duration;
otherwise the clearing of the stimulus would occur too early (i.e., at the start of the PreRelease
time). This is rarely a problem in practice, as the clearing of the current stimulus is typically
performed by the drawing of the next object in the sequence, and most experiments can be easily
re-organized to fit this model.
Similarly, PreRelease time cannot be honored by E-Prime in the case that the current object is
terminated by a response input (i.e., because the system cannot possibly predict when a subject
will respond, it cannot react to the response until after it occurs). This also is typically not a
problem for most paradigms, as once a display is terminated, subsequent displays are not often
viewed as time critical. Note, even if they are, they are minimally likely to be out of sync with the
vertical refresh cycle, and incur some amount of unwanted delay. For paradigms in which this is
a problem, it is recommended that the input specifications be set so that the display is NOT
terminated upon response. This will allow the response to be time-stamped, scored, and logged
properly, and the timing of the display sequence will remain accurate.
3.3.1.2 Technique 2: Synchronization to the refresh cycle of
the monitor
You should always present stimuli for integer multiples of the refresh cycle of the monitor, which
synchronizes stimulus presentation with the refresh cycle. In order to understand the role of this
second technique, we need to examine the way in which computers display visual stimuli on their
monitors. Although the picture is actually drawn by a light beam that moves across the screen,
we can conceptualize the computer as presenting a series of static frames at a fixed rate. In this
conceptualization, the display is like a motion picture film, where each frame is typically presented
for between 1/60th to 1/85th of a second. Presentation time comes in discrete units within the
refresh cycle of the display. All displays take place with respect to refresh cycles. Refresh cycles