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PAMELA SADLER AND ERIK Z. WOODY
those imagery trials, and the corresponding value for the effortful sug-
gestion wording was obtained by averaging the other three imagery
trials. Preliminary analyses showed that neither the order of the two
types of suggestions nor gender had any significant effects; therefore,
these factors were omitted from the statistical models reported below.
For each participant, baseline heart rates prior to the effortless
and effortful imagery suggestions were calculated by averaging the corre-
sponding three baseline values. A GLM on these baseline heart rates
showed no significant effects for hypnotizability, suggestion wording, or
their interaction. To reduce error variance, we used these two baseline
heart-rate measures as covariates in the main analysis. This GLM, with the
within-subject variable of suggestion wording (effortless vs. effortful) and
the between-subject variable of hypnotizability (low vs. high), yielded the
predicted interaction of suggestion wording by hypnotizability,
F
(1, 44) =
6.48,
p
= .01,
h
2
= .13. Neither of the main effects was statistically significant.
Figure 1 shows the adjusted means for this interaction. Effortful
suggestion wording, compared to effortless wording, led to a greater
increase in heart rate for low hypnotizable participants (
M
= 4.84,
SE
=
0.87, vs.
M
= 3.44,
SE
= 0.77), but not for highs (
M
= 2.74,
SE
= 0.83, vs.
M
= 3.23,
SE
= 0.74). Simple effects analysis verified that for lows the
heart-rate increase was significantly greater for the effortful versus
effortless suggestion wording,
t
(44) = 1.79, one-tailed
p
< .05; whereas
no such effect occurred for highs. This is the pattern we predicted in
accordance with dissociated-control theory (Prediction 3b).
Figure 1.
Heart-rate increase during imagery as a function of hypnotizability and
suggestion wording.
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