User`s guide

E-Prime User’s Guide
Chapter 3: Critical Timing
Page 109
Timing Paradigm 3. Critical sequence of events with varying duration of
Probe
Another common paradigm is presenting displays for varying durations in order to map out a
psychological function. For example, mapping the accuracy for words as a function of display
duration, with displays being presented at 17, 33, and 50ms. This can be accomplished with a
modest variant of Paradigm 2. By setting the display time as an independent variable, the
duration of the Probe can be manipulated. Any display time used must be an integer multiple of
the refresh cycle. In this example, the refresh rate was measured to be 60.16Hz, which provides
a refresh duration of 16.62ms. Applying the rule of thumb outlined in section 3.4.2.1 results in a
Duration setting of 7ms for a single refresh. The table below shows the appropriate Duration
settings for 1-3 refresh cycles.
Number of Refresh Cycles 1 2 3
Refresh Time 16.62 33.24 49.86
Rounded 17 33 50
Rounded-10 7 23 40
To alter the stimulus duration, set an attribute for the ProbeDuration in a List object within E-
Studio. The values for the ProbeDuration attribute will be the rounded refresh time minus 10ms.
Figure 19 below shows the outline of the experiment with a List object that sets the
ProbeDuration.
Figure 19. TrialList with a ProbeDuration attribute set to vary onset time. The ellipse shows the time critical parts of the
experiment.
On the Duration/Input tab of the Probe object, the Duration must now be set to [ProbeDuration] so
the program gets the duration for the ProbeDuration variable from the experiment context. On
each trial, the experiment selects a row from the TrialList, sets the Probe Duration field to the
value of the [ProbeDuration] attribute, and then executes the sequence of displays to present the
stimulus. The arrow in the next figure shows where the Duration was specified on the Probe
display.