User`s guide

E-Prime User’s Guide
Chapter 3: Critical Timing
Page 103
Timing Paradigm 3: Critical sequence of events with varying duration of
Probe
This paradigm is a variant on Paradigm 2 in which the duration of an event in a sequence varies
between trials (e.g., the duration of the probe would be 14, 28 or 42ms – integer multiples of the
refresh rate). This paradigm includes a parameter in a List object to set the duration as an
independent variable. The Durations must be based on the refresh rate of the video mode.
Timing Paradigm 4: Cumulative timing of a repeating sequence of events
This paradigm presents a long series of events, and seeks to maintain cumulative timing
accuracy such that there is no drift in the timing. An example would be presenting a continuous
performance task to check random letters that occur every second for ten minutes, and to
respond whenever an “X” occurs. Even after hundreds of stimuli, the criterion of each stimulus
occurring precisely on one second boundaries must be met (i.e., a new stimulus must be
presented every second). The timing may have to maintain millisecond scaling with an external
recording device (e.g., ERP or MRI biological recording device). In this model, all of the events in
some repeating loop of presenting stimuli are critical. This paradigm model uses Cumulative
timing mode with PreRelease used for all events in the repeating loop. The event before the
beginning of the repeating loop should also have a PreRelease to avoid any timing delays in the
presentation of the first stimulus of the first trial. This paradigm model also typically prohibits the
termination of stimuli based on a subject response.
Timing Paradigm 5: Continuous sequences of events at high rate with short
stimulus times
This paradigm involves presenting stimuli typically at a high rate in some form of continuous loop
(e.g., presenting pictures at 50ms each for a fast rotating checkerboard). In this case, all of the
events in the procedure loop are time critical. All events must occur for specified durations, and
subject input typically does not alter the timing (i.e., a response does not terminate a display).
This paradigm model is similar to Paradigm 4, but because of the short stimulus presentation
times, it introduces the concept of preloading or caching stimuli because it cannot rely on the use
of PreRelease to maintain consistent timing (i.e., because of the high rate of presentation, there
may not be enough time available between stimulus presentations for the use of PreRelease to
have any real effect).
The same basic experimental procedure can operate at all of these levels of criticality, depending
on the experimental requirements. We will illustrate all of these modes with a lexical decision
experiment for paradigms 1-4 and a rotating visual stimulus for paradigm 5 (continuous rotating
checkerboards). In the lexical decision experiment, the subject is presented with a string of
letters that form a word (“cat”) or non-word (“dob”). In Paradigm 1, the word is presented and the
time of the response is collected without other critical timing constraints. In Paradigm 2, a
sequence of fixation, probe, and mask is presented where the fixation-probe and probe-mask
intervals are critical. In Paradigm 3, the sequence of fixation, probe, mask, and feedback is
presented where the probe is displayed for varying durations. In Paradigm 5, a stream of stimuli
is presented at a high rate of 20 stimuli per second to keep a checkerboard pattern rotating
smoothly.
3.4.2.4 Implement a critical timing paradigm
Timing Paradigm 1: Single stimulus event to response timing
This paradigm displays a single stimulus event and collects a single response. Use a stimulus
presentation object (TextDisplay, ImageDisplay, Slide, or SoundOut) in the procedure with Event
timing mode and without PreRelease. The duration for each event will be what is specified in the