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ROLE OF COGNITIVE EFFORT
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Procedure
Participants completed the experiment individually. They were told
that the experiment would explore the relationship between hypnotic
imagery and physiological measures; however, the actual physiologi-
cal variable monitored (heart rate) was not explicitly mentioned until
the end of the experiment. Participants were asked to refrain from caf-
feine or nicotine intake for 1 hour prior to the experiment to ensure
that these stimulants would not affect heart-rate measures.
After the chest band was secure, the participant was asked to sit qui-
etly and to minimize the amount of movement for the duration of the
experiment. Some filler tasks were completed to allow for an ample
period of adaptation, and then a standard hypnotic induction was
administered. By this time, the participant had been seated for about
20 minutes.
After the hypnotic induction was complete, the participant was
asked to sit quietly and to think of nothing in particular for about 2
minutes. The participant was also told that if any stray thoughts
occurred, to let them pass, giving them very little attention, in order to
return to a quiet mind once more. The last minute of this period was
used as the first baseline for the heart-rate data.
Six different imagery scenes designed to be approximately equiva-
lent were administered to each participant. Each scene involved imag-
ining a different animal. The suggested images were designed to be
particularly low in fearfulness and activity level, because these are
other aspects of imagery that may affect heart rate (e.g., Bauer &
Craighead, 1979; Jones & Johnson, 1980). The order of the scenes was
counterbalanced.
The wording of the imagery suggestions was effortless for three of
the scenes and effortful for the other three scenes. To illustrate this
manipulation, the order of which was also counterbalanced, here is an
example of the same scene phrased using the effortless and effortful
suggestion wording:
Effortless
. Let yourself imagine a zebra on a hot dry plain slowly saunter-
ing along a row of bushes. Let this image just occur to you, just like
watching a movie where events may occur gradually or spontaneously,
just happening of their own accord.
Effortful
. Make this scene happen through your own will and effort, main-
taining control of the image: Try as hard as you can to imagine a zebra on
a hot dry plain slowly sauntering along a row of bushes. Try to maintain
control over this image. But if something unintended happens, let it pass
and continue to make the animal do only what you want it to do.
Each imagery trial lasted for 1 minute. Testing with pilot partici-
pants indicated that imagery tends to begin within 2 to 3 seconds
after the animal is mentioned; therefore, the 1-minute imagery trials
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